Gemstones of The World - Schumann, Walter [PDF]

Zitiervorschau

revised

,

expanded EDITION

Walter

Schumann

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Precious and .

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Semiprecious Stones 1,500 Photos of

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Gems

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Rough and

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Polished States

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Complete Physical Properties and Characteristics

Finding, Mining

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and Cutting

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Triangle

Hexagon

Antique

Needle

brilliant

Recoupe-rose

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Baguette

Drop

Half-brilliant

Simple rose Jubilee cut

Free form

Coat-of-arms

Magna

Briolette

cut

Shield

Square

Ceylon cut Petal cut

Star brilliant

Square

Antique French cut

Pear-shaped

Double

Star cut

brilliant

Swiss cut

Olive

American cut

Octagon

Rhomb

Highlight brilliant

Double rose Oval

Pentagon

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Gemstones of the World Revised

&

Expanded Edition

Walter

Schumann

BR BR

QE392 .S54513 1997

// Sterling Publishing Co., Inc.

New York

1

Contents

Luster 41

Pleochroism 41 Light and Color Effects 44 Luminescence 47

7

Preface

8

Introduction

Inclusions 49

52

Terminology 10

of Gemstones

The Nomenclature ofGemstones 14

Types of Deposits 53

12

Origin and Structure

Mining Methods 55 58

of Gemstones

Cutting and Polishing of

Crystal Systems 17

19

Deposits and Production

Gems

Engraving on Stones 59

Properties of Gemstones

Cutting and Polishing Agate 60

Hardness 19

Cutting and Polishing Colored Stones 61

Cleavage and Fracture 22

and Cylinder Cutting 62

Weights Used in the Gem Trade 26

Ball

Optical Properties 27

Cutting and Polishing

Drilling

Color 27 Color of Streak 28 Color Change 28 Refraction of Light

Gemstones 63

Diamond 64 Types and Forms of Cut 66 3

Double Refraction 34

68

Dispersion 35

Description of Gemstones Scientific Classification 68

Absorption Spectra 37

Commercial

Transparency 41

70

Best

Classification

69

Known Gemstones

Diamond Diamond Diamond Diamond

70 Occurrences 72 Production 73

Trade 74

Valuation of Diamonds 76

Famous Diamonds 78 Development of the Brilliant Cut 80

Corundum

3

6

Ruby 82

8

Sapphire 86

Amethyst Amethyst Quartz

Beryl 90

Citrine 120

Emerald 90 Aquamarine 94 Beryl 96 Chrysoberyl 98

Prasiolite

1

Common Opal

1

1

18

154 Nephrite 156

Jadeite

120

Rose Quartz 122

Peridot 158

Aventurine 122

Zoisite 160

Prase 122

Tanzanite 160

Blue Quartz 122

Thulite 160 Anyolitc 160

Spessartine 104

Quartz Cat's Eye 124 Hawk's Eye 124 Tiger's Eye 124 Chalcedony 126 Cornelian 126

Grossular 106

Sard 126

Moonstone 164

Andradite 106

Chrysoprase 128 Heliotrope 128 Dendritic Agate 130 Moss Agate 130 Agate 132 Jasper 146 Fossilized Wood 148

Orthoclase 164

Spinel

100

Topaz 102 Garnet 104 Pyrope 104 Almandine 104

Uvarovite 106

Zircon 108 Tourmaline 110

Spodumene 114 Hiddenite 114 Kunzite 114

Quartz 116

Opal 150 Precious Opal Fire Opal 152

Rock Crystal 116

Smoky Quartz

1 1

178

Lesser

Hematite 162 Pyrite 162

Feldspar 164

Amazonite 164

Labrador ite 166 Aventurine Feldspar 166

Rhodochrosite 168

Rhodonite 168 Turquoise 170 Lapis Lazuli 172 Sodalite 174

1

50

Azurite 174

Malachite 176

Known Gemstones

Andalusite 178

Amblygonite 192

Euclase 178

Enstatite 192

Hambergite 180

Lazuli te 192

Cordierite 180

Dioptase 194

Phenacite 180

Apatite 194

Dumortierite 182 Danburite 182

Titanite 194

Kyanite 196

Axinite 182

Scheelite 196

Benitoite 184

Variscite 196

184 Epidote 184

Hemmimorphite 198

Vesuvianite 186

Smithsonite 198

Sinhalite 186

Sphalerite 200

Kornerupine 186

Cerussite 200

Prehnite 188

Chrysocolla 200

Fluorite 198

Cassiterite

Petalite

Serpentine 202

188

Scapolite 188

Stichtite

Diopside 190

Ulexite 202

Beryllonite 190

Tiger's

Brazilianite

204

152

Jade 154

190

Gemstones

for Collectors

202

Eye Matrix 202

8

2

1

8

Rocks

as

Gemstones

Onyx Marble 218 Tufa 218 Landscape Marble

2

1

Orbicular Diorite 220 Kakortokite 220

Obsidian 220 Moldavite 220 Alabaster 222

Agalmatolithe 222

Meerschaum 222 Fossils 222

224

Organic Gemstones Coral 224

Gagate 226 Cannel Coal 226 Ivory 226 Odontolite 226 Amber 228 Pearl 230

240

New on the Market Verdite 240

Charoite 240

Gneiss 240

Unakite 240

Nuummite 240 Ammolite 240 Carletonite 240 Katapleite 240 Sugilithe 240 Gaspeite 240

242

Imitation Gemstones Imitations 242

Combined Stones 243 Synthetic Gemstones 243

Gemstones 243 Checking for Genuineness of Diamond 246

247

Symbolism of Stones

249

Table of Constants

267

Index

From the Preface to the Gemstones have always

First Edition

fascinated mankind. In former centuries they were reserved

Today everybody can afford beautiful stones for jewelry and adornment. Precious stones for sale, especially if one includes those in so-called costume or fashion jewelry, are so numerous that it is hardly possible for the layman to survey or judge what is available. This little book has been written to help: it shows the many gems of the world in their many varieties, rough and cut, in true-to-nature color photographs. The accompanying text — always adjacent to the photographs — is designed to be of use to both the expert and the layman. Introductory chapters on formation, properties, deposits, manufacture, synthesis and imitations provide a survey of the world of beautiful stones. Unknown gemstones can be identified with the help of the tables at the end of the book. I received valuable help from professional colleagues, friends and acquaintances, institutes, firms and private persons who made stones available for illustration. My thanks are due to all of them with special thanks to Mr. Paul Ruppenthal, IdarOberstein. I also thank Mr. Karl Hartmann, Sobernheim, for taking the special photographs. for the ruling classes only.

& Expanded

Preface to the Revised

Edition

Gemstones ofthe World has been translated into a dozen languages. The total number of copies worldwide approaches the million mark. This revised and expanded edition is larger in

volume and brought up

to date with current data and scientific knowledge.

My thanks are due again to the company A. Ruppenthal KG, Idar-Obertsein, for Hans Walter Lorenz, of the newly shown gemstone-collector's so that they could be photographed. Walter Schumann

their great willingness to help.

Idar-Oberstein, rarities

who

I

further say thank you to Mr.

especially cut

many

The Presentation of the Text When describing gemstones, my objective as possible.

has been to provide as much information Therefore, in part, smaller letter-types were used, short forms were

chosen, and repetitions, which would take up space, were avoided.

The meaning of abbreviations, as well as the omission of the units of measurements are clearly recognizable from the respective context.

Comment: The

data and recommendations in this

research and experience over

many

book

years by the author.

are based

The

on

extensive

author and/or the publishing company cannot be held liable for any errors or omissions and cannot be held responsible for how the reader chooses to use this information.

Introduction Gemstones and Their Influence Gems have intrigued humans for at least 10,000 years. The first known, used for making jewelry, include amethyst, rock crystal, amber, garnet, jade, jasper, coral, lapis lazuli, pearl, serpentine, emerald, and turquoise. These stones were reserved for the wealthy, and served as status symbols. Rulers sealed documents with their jewelencrusted seals. Such treasures can now be admired at many museums and treasurevaults.

Today, gems are not so

much worn

to demonstrate wealth, but jewelry

is

bought

increasingly for pleasure, in appreciation of its beauty.

when purchasing a gemstone, a certain love for a special when people were less scientifically knowledgeable, gems always had an aura of mystery, something almost spiritual. That's why they were worn Certainly, also today,

stone

is

part of it. Formerly,

amulets and talismans. Up to the beginning of the 19th century, gemstones were sometimes used as remedies against illnesses. They could be used in three different ways: the mere presence of the stone was sufficient to effect a cure; the gem was placed on the afflicted part of the body; or the stone was powdered and eaten. Even today, calcium tablets made from crushed pearls are sold for medicinal purposes. Presently, medical science is experiencing worldwide a revival of the ideas of the Middle Ages in the use of precious stones through the doctrines of the Esoterics. Gems also have an assured place in modern religion. The breastplate of the high priests of Judea were studded with four rows of gemstones. Precious stones adorn the tiara and miter of the Pope and Bishops as well as the monstrances, reliquaries, and icons found in Christian churches. All major religions use precious stones, be it as decoration for tools or adorning buildings. As a capital investment, however, of all gemstones really only diamonds are suitable. In fact, these have proven to hold on to their value, despite the travails of war or depressions in the economy. as

The English Imperial State Crown with

rubies, emeralds, sapphires, pearls,

and more than 3000

diamonds. the center below "Cullinan II." (or "Lesser Star of Africa") with 317.40ct. It is the seconddiamond in the world, having 66 facets. It was won from the largest raw diamond ever found, the "Cullinan," besides 104 other split pieces. The company Asscher in Amsterdam polished it (compare also "Cullinan I.," page 78, No. 3). The large red stone above "Cullinan II." is the so-called "Black Prince's Ruby." Once thought to be a ruby, it is, in fact, a spinel, uncut, only polished, 2in (5cm) high. The State Crown is exhibited in the Tower of London. In

largest polished

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Terminology In the following, important terms of the trade, used throughout the book, are explained:

There is no generally accepted definition for the term precious have something special, something beautiful, about them. Most of the precious stones are minerals (e.g., diamond), rarely mineral aggregates (e.g., lapis lazuli) or rocks (e.g., onyx-marble). Some precious stones are organic formations (e.g., amber); others are of synthetic origin. There is no definite demarcation line, and woods, coal, bones, glass, and metals are all used as precious stones for ornamentation. Some examples include jet (a bituminous coal), ivory (tusks of elephants as well as teeth of other large animals), moldavite (glassy after-product of the striking of a meteorite), and gold nugget (more or less large gold-lumps). Even fossils are sometimes used as ornamental material. For some precious stones the source of specialness and beauty is the color, the play of color, or the shine that makes them stand out in comparison to other stones. For other stones it is the hardness or an interesting inclusion that makes them special. Rarity also plays a role in the classification as gemstone. Since the valued characteristics usually come into effect only through cutting and polishing, gemstones are also always considered to be the cut stones. Cutting and polishing means refinement of an otherwise insignificant raw material. There are several hundred independent types of gemstones. The number of the variations is about double that. From time to time, new gemstones are discovered or varieties with gemstone quality are found in minerals which have been already known. Harder stones are suitable for jewelry, whereas softer stones are often sought after by amateur collectors as well as serious lapidarists. Precious Stone

stone, but they

Gemology

all

Internationally, the science of precious stones

is

most commonly

re-

ferred to as gemology.

Colored precious stone is a new term of the trade for all noncolored) precious stones, except for diamonds, formerly called colored stone. In rJie processing of stones, one understands by the term colored stones all precious stones except agate and diamond.

Colored Precious Stone (also for

Rock A rock is a natural aggregate of different or also of the same minerals. It forms independent geological bodies of large expanse and includes crystalline or cemented hard rocks as well as accumulated loose material such as sand or gravel that is not cemented.

The term semi-precious has generally fallen out of use derogatory meaning. Formerly, one meant with this term the less valuable and not very hard precious stones, which one opposed to the "real" precious stones. "Real" and "semi-precious" are adjectives, however, that cannot be adequately Semi-precious Stone because of

its

defined to distinguish between precious stones.

Imitation Imitations are made to resemble natural or synthetic precious stones, completely or partially manmade. They imitate the look, color, and effect of the original substance, but they possess neither their chemical nor their physical characteristics. To these belong — strictly speaking — also those synthetic stones that do not have a counterpart in nature (for instance, fabulite or YAG). In the trade, these, however, are often counted as synthetic precious stones.

10

Jewel

Every individual ornamental piece

piece of jewelry containing one or

is

a jewel. Generally, a jewel refers to i

more gems set

in precious metal.

Sometimes,

it

can

also refer to cut, unset gemstones.

Crystal

A crystal

the smallest

The

is

a

uniform body with an ordered structure, i.e., a (the atoms, ions, or molecules) in a geometric

components

strict

order of

crystal lattice.

varying structures of the lattice are the causes of the varying physical properties

of the crystals and therefore also of the gems.

Crystallography

A

Mineral

Crystallography

mineral

is

a naturally

is

occurring, inorganic, solid constituent of the

earth's (or other celestial body's) crust.

Mineralogy

Mineralogy

Petrography

is

Petrography

the science of crystals.

Most minerals have

the science of minerals. is

the descriptive science of rocks, typically utilizing a

petrographic microscope or other instruments.

more comprehensively

to

definite crystal forms.

mean

The term

petrography

is

often used

the same as petrology.

Petrology Petrology is the science of the origin, history, occurrence, structure, chemical composition, and classification of rocks. Sometimes petrology is loosely used to mean the same as petrography.

Gemstone The term gemstone is generally used as a collective name for all ornamental stones and stone-similar materials. In a more restrictive sense, it is used as a term only for the less valuable or opaque stones. Commonly, the word gemstone is understood synonymously for any precious stone in general. There is no convincing demarcation line between more or less valuable stones. Therefore it is often appropriate to speak summarily of gemstones, rather than of precious or semi-precious stones. Stone

Popularly, stone

is

the collective

name

for

all

solid constituents of the earth's

For the jewelers and collectors of precious stones, the word stone means only precious- or gemstones. For the architect, on the other hand, it means the material used for constructing buildings and streets. In the science of the earth, geology, one does not talk of stones, but of rocks and minerals. crust except for ice and coal.

Synthesis

Short term for

a synthetic precious stone.

Synthetic Precious Stone Synthetic gemstones (in short called syntheses) are crystallized manmade products whose physical and chemical properties for the most part correspond to those of their gemstone counterpart. Unjusdy, this term is also used by the gemstone trade for those synthetic stones which do not have a counterpart in nature (for instance, fabulite or YAG). In fact, these stones are properly termed imitations.

By a variety, one understands in the case of precious stones a modification which distinguishes itself through its look, color, or other characteristics from the actual gemstone type.

Variety

11

The Nomenclature of Gems The

oldest names for gemstones can be traced back to Oriental languages, to Greek and to Latin. Greek names especially have left their stamp on modern gem nomenclature. The meaning of old names is not always certain, especially where the first meaning of the word has been changed. Also, in antiquity, totally different stones were given the same name simply because they may have had the same color. Original names referred to special characteristics of the stones, such as color (for instance "prase" for its green color), their place of discovery ("agate" for a river in Sicily), or mysterious powers ("amethyst" was thought to protect against drunkenness). Many mineral names, which were later also used to name gemstones, have their origin in the miners' language of the Middle Ages. Nomenclature has only been viewed scientifically since the beginning of the modern age. Because of the discovery of many hitherto unknown minerals, new names had to be found. A principle for naming new minerals and gemstones was established which is still adhered to today. A new name is devised to refer to some special characteristic of the mineral, based on Greek or Latin, the chemical constituents, the place of occurrence, or a person's name. Through such name-giving, not only experts are honored, but also patrons or others who may or may not have any connection with mineralogy or gemology. But since everyone did not always agree when a name was given, various names for the same mineral have come into use and persist to this day. The gemstone and jewelry trade added more of their own names, mainly to stimulate sales, producing a large number of synonyms and variety names for gemstones. In order to correct this state of affairs, all newly discovered minerals, as well as the intended new names, must now be presented for evaluation to the Commission on New Mineral Names of the IMA (International Mineralogical Association), to which experts from all over the world belong. Anyone who believes that he has found a new mineral or an important gemstone variety must have his first right and other legalities as well as the name-giving checked. Only then is the name of the mineral and/or the gemstone sanctioned and

standardized.

Since in the gemstone trade, the danger of purposefully giving a wrong name and improper evaluation of goods is especially high, the Commission for Delivery Conditions and Quality Securing at the German Norm Commission has published in 1963 / 70 in the RAL A5/A5E Guidelinesfor Precious Stones, Gemstones, Pearls and Corals (for

Germany)

to protect against unfair competition.

Internationally, permitted definitions

and the trade customs for gemstones are

regulated through the International Association Jewelry, Silverwares, Diamonds,

and Stones, in short CIBJO (Confederation Internationale de la Bijouterie, Diamants, Perles, et Pierres). Certainly, the aforementioned institutions have led to better communication and to more security for the gemstone buyer and seller, but such measures, naturally, cannot enforce an absolute guarantee for genuineness. Pearls,

Joaillerie, Orfevrerie, des

False False

and Misleading Names of Some Gemstones Gemstone Name

Adelaide ruby African emerald Alaksa diamond

American jade 12

Correct Mineralogical Almandine Green fluorite Rock crystal Green vesuvian

Name

American ruby

Pyrope, almandine or rose quartz

Arizona ruby Arizona spinel Arkansas diamond Balas ruby

Pyrope

Red or green garnet Rock crystal

Blue alexandrite

Pink spinel Blue or violet sapphire

Blue moonstone

Artificially blue-tinted

Bohemian chrysolithe Bohemian diamond Bohemian ruby

Moldavite

Brazilian

aquamarine

Brazilian ruby Brazilian sapphire Ceylonesian diamond Ceylonesian opal

German diamond German lapis Gold topaz

chalcedony

Rock crystal Pyrope or rose quartz Bluegreen topaz Pink topaz Blue topaz Colorless zircon

Opal-like glimmery moonstone

Rock

crystal

Artificially blue-tinted jasper

California ruby

Citrine or yellowish fired amethyst Aventurine Hessonite

Candy

Almandine

Indian jade spinel

Cap-chrysolithe

Green prehnite

Cap-ruby

Pyrope

King's topaz

Reddish-yellow corundum Serpentine Dioptaz Kunzite Hiddenite Citrine or yellowish fired amethyst

Korean jade

Copper

sapphire'

Lithion amethyst

Lithion emerald Madeira topaz

Marmarosch diamond Matura diamond Mexican diamond Mexican jade Montana ruby

Rock

crystal

Colorless fired zircon

Rock

crystal

Artificially tinted

green limestone

Red garnet

Oriental amethyst

Violet spinel

Oriental hyazinth

Palmyra topaz

Pink sapphire Yellow sapphire Citrine or yellowish fired amethyst

Smoky

Smoky

Oriental topaz

topaz

Saxon chrysolithe Saxon diamond Salmanca topaz Serra topaz

Siamese aquamarine Siberian chrysolithe Siberian ruby

quartz

Greenish-yellow topaz Colorless topaz Citrine or yellowish fired amethyst Citrine or yellowish fired amethyst Blue zircon

Demantoide Red tourmaline

diamond

Glass imitation

Slave-diamond Spanish topaz

Colorless topaz

diamond

Glass imitation

Simili

Strass

Citrine or yellowish fired amethyst

Transvaal jade Ural sapphire

Green grossular Demantoide

Viennese turqoise

Artificially blue-tinted

argillaceous earth

13

Origin and Structure of

Since, with

Gemstones

few exceptions, most gemstones are minerals, it is the origin and structure The formation of the nonmineral geminstance, amber, coral, and pearl) will be dealt with in more detail when

of minerals that concerns the gemologist. stones (for

they are described.

Minerals can be formed in various ways. Some crystallize from molten gases of the earth's interior or from volcanic lava streams that reach the earth's surface (magmatic minerals). Others crystallize from hydrous solutions or grow with the help of organisms on or near the earth's surface (sedimentary minerals). Lastly, new minerals are formed by recrystallization of existing minerals under great pressure and high temperatures in the lower regions of the earth's crust (metamorphic

Origin

magma and

minerals).

The chemical composition of the minerals is shown by a formula. Impurities are not included in this formula, even where they cause part or total color change of the stone.

Formations of Crystals Nearly all minerals grow in certain crystal forms, i.e., they are homogeneous bodies with a regular lattice of atoms, ions, and molecules. They are geometrically arranged and their outer shapes are limited by flat surfaces (in the ideal case), resulting in crystal faces.

Most crystals are small, sometimes even microscopically small, but there are also some giant specimens. In general, the smallest minerals (due to their tiny size) as well as the giant

minerals (due to their inclusions, impurities, or uneven growth marks ) are

unsuitable as gems.

its

The inner structure, the lattice, determines the physical properties of the crystal: outer shape, hardness, cleavage, type of fracture, specific gravity, and optical

properties.

Crystal lattice of

14

diamond

Rubellite step,

Madagascar (% natural

size).

an irregular form, because some have developed better at the cost of others; however, the angle between the faces always remains constant. When individual single crystals occur in combination with other crystal forms, e.g., hexahedron with octahedron, the identification of a mineral on the basis of crystal shape can be extraordinarily complicated. The arrangement of faces preferred by a mineral is called the "habit"; for instance, pyrite is often found in the shape of a pentagon dodecahedron, garnet, as a rhombdodecahedron. The habit of a crystal also refers to its type and can be tabular, acicular, foliated, columnar, or compact. For the benefit of laymen, the technical terms, habit and form, are sometimes called structure. Sometimes minerals occur in unusual, for them, crystal forms. These are called pseudomorphs. They can originate due to chemical alteration or through exchange processes. Where two or more crystals are intergrown according to certain laws, one speaks of twins, triplets, or quadruplets. Depending on whether the individual crystals are grown together or intergrown, one speaks of contact twins or penetration twins. Apart from twinning which adheres to certain laws, many crystals are irregularly intergrown into aggregates. Depending on the growth process, filiform (wire-like), fibrous, radial-shaped, leaf-like, shell-like, scaly, or grainy aggregates are formed. According to miners' lingo, a mineral aggregate with free-standing individual crystals

Most

crystals are not regularly shaped, but have

crystal faces

is

called "step."

Well developed, characteristic minerals are formed as druses on the inner walls of rock openings (geodes); these are mainly round hollows created by gas bubbles in

magmatic rocks or spaces where organic material has been removed

in

sedimentary

rocks.

Crystal systems distinction

On

page

is

17,

In crystallography, crystals are divided into seven systems.

The

made according to crystal axes and the angles at which the axes intersect. the crystal systems are depicted with some typical crystal formations.

Cubic system

(regular system)

All three axes have the

same length and interrhombic

sect at right angles. Typical crystal shapes are the cube, octahedron,

dodecahedron, icosi-tetrahedron, and hexacisochedron.

15

Tetragonal system The three axes intersect at right angles, two are of the same length and are in the same plane, while the main axis is either longer or shorter. Typical crystal shapes are four-sided prisms and pyramids, trapezohedrons and eightsided pyramids as well as double pyramids.

Hexagonal system

Three of the four

and intersect each other

at

axes are in one plane, are of the same length, an angle of 120 degrees. The fourth axis, which is a

is at right angles to the others. Typical crystal shapes are hexagonal prisms and pyramids, as well as twelve-sided pyramids and double pyramids.

different length,

Trigonal system

(rhombohedral system) Axes and angles are similar to the preceding system, therefore the two systems are often combined as hexagonal. The difference is one of symmetry. In the case of the hexagonal system, the cross section of the prism base is six-sided; in the trigonal system, it is three-sided. The six-sided hexagonal shape is formed by a cutting-off" process of the corners of the triangles. Typical crystal forms of the trigonal system are three-sided prisms and pyramids, rhombohedra, and scalenohedra.

Orthorhombic system

(rhombic system)

Three

axes of different lengths are at

right angles to each other. Typical crystal shapes are basal pinacoids, rhombic prisms

and pyramids

as well as

Monoclinic system

rhombic double pyramids.

The

three axes are each of different lengths, two are at right

angles to each other, and the third one

is

inclined. Typical crystal forms are basal

pinacoids and prisms with inclined end faces.

Triclinic system

All three axes are of different lengths and inclined to each other. Typical crystal forms are paired faces.

In the table on page

18,

minerals from which

many gemstone

varieties

come

are

allocated to their respective crystal systems.

Horizontal

which

is

gemstone microscope.

In

the center of the apparatus

held by a movable claw holder.

is

a box with a red gemstone,

Crystal

Systems

cubic

u

tetragonal

i

hexagonal and trigonal

w orthorhombic

monoclinic

triclinic

>^W 17

Selected

Gemstones

Ordered by Crystal System cubic

hexagonal

orthorhombic

Hornblende

Almandine Analcime

Apatite

Adamine

Jadeite

Aquamarine Benitoite

Cuprite

Beryl

Alexandrite Andalusite Anglesite

Klinohumeite

Andradite

Demantiod Diamond

Cancrinite

Howlite

Anhydrite Aragonite

Klinozoisite

Krokoite Kunzite

Fabulite

Emerald Greenockite Jeremejewite

Fluorite

Milarite

Celestite

Legrandite Malachite Mesolite

Gahnite

Nepheline

Cerussite

Moonstone

Gallinat

Painiate

Chrysoberyl

Muskovite

Garnet Gold

Precious beryl

Cordierite

Simpsonite

Danburite

Grossular

Sugilithe

Desclsizite

Nephrite Neptunite Orthcclase

Hauynite Hessonite

Taaffeite

Thaumasite

Diaspor Dumortierite

Lapis Lazuli

Zincite

Enstatite

Djevalite

Magnetite Melanite

Boracite

Eosphorite

Periclase Pollucite

Barite

trigonal

Lazulite

Petalite

Phosphopyllite Sapphirine Serpentine

Spodumene

Hambergite Hemimorphite Hypersthene

Telk

Staurolite

Kornerupine

Titanite

Pyrope Senarmontite

Agate Amethyst

Lithiophilite

Tremolite

Manganotanitalite

Vivianite

Silver

Aventurine

Meerschaum

Vlasovite

Sodalite

Calcite

Nathrolite

Spessartite

Catapleite

Peridot

Whewellite Yugawaralite

Sphalerite

Chalcedony Chrysopase Cinnabar

Prehnite

Sulphur

Citrine

Sinhalite

Pyrite

Spinel

Topazolithe Tsavolithe

Purpurite triclinic

Uvarovite

Cornelian

Strontianite

YAG

Corundum

Tansanite

Amazonite Amblygonite

Zirconia

Dioptase Dolomite

Tantalite

Andesine

Thulite

Aventurine feldspar

Friedelite

Topaz

Axinite

Gaspeite Hematite

Triphyline

Davidite

Jasper

Witherite

Kyanite

Magnesite

Zoisite

Parisite

Zectzerite

Labradorite Microcline

tetragonal Anatase Apophyllite

Variscite

Kurnakovite

Boleite

Phenakite

Montebrasite

Carletonite

Prasiolithe

Oligoclase

Eudialyte

Proustite

Cassiterite

Pyrargyrite

Chalcopyrite

Quartz Rhodochrosite Rock crystal Rose quartz

Leucite

Melinophane Phosgenite

monoclinic

Pectolite

Aegirinaugelite

Azurite

Sanidine Turquoise

Barytocalcite

Ulexite

Rhodonite

Beryllonite

Pyrolusite

Ruby

Brasilianite

Rutile

Sapphire

Charoite

Scapolithe

Siderite

Colemanite

Scheelite

Smithsonite Smoky quartz

Diopside Epidote Euclase

Tugtupite Vesuvian

Wardite Wulfenite Zircon

18

Stichite

eye Tourmaline Willemite Tiger's

amorphous Amber

Gypsum

Chrysocolla Ekanite Moldavite Obsidian

Hiddenite

Opal

Gaylussite

Properties of

Gemstones

knowledge about the most important properties of gemstones are of inestimgemstone cutter and the setter, as well as to the wearer of the jewelry and the collector. Only with proper knowledge can one correctly work the gemstone, make use of it, and take care of it. Specific

able value to the

Hardness In the case of minerals and gemstones, hardness refers

first

to scratch hardness, then to

cutting resistance.

Scratch Hardness mineralogist Friedrich Mohs (1773-1839) introduced the term scratch hardness. He defined the scratch hardness as the resistance of a mineral when scratched with a pointed testing object. Mohs set up a comparison scale using ten minerals of different hardnesses (Mohs' hardness scale), which is still widely in use. Number 1 is the softest, number 10 the hardest degree. Each mineral in the series scratches the previous one with the lesser hardness and is scratched by the one which follows after. Minerals of the same hardness do not scratch each other. In practice, the hardness grades have also been subdivided into half degrees. All minerals and gemstones, known to us today, are allocated to Mohs' hardness scale. (See table, page 21.) Gemstones of the scratch hardness (Mohs' hardness) 1 and 2 are considered soft; those of the degrees 3 to 5 medium hard; and those over 6 hard. Formerly, one spoke also of gemstone hardness in regards to the steps 8 to 10. This is no longer in use, since there are valuable gemstones that do not have these high Mohs' hardness values. The luster and polish of gemstones of the Mohs' hardness below 7 can be damaged by dust, as this may contain small particles of quartz (Mohs' hardness 7). Through the scratching of this quartz dust, the stones become mat in the course of time. Such stones must be carefully handled when being worn and stored.

The Viennese

Relative

and Absolute Hardness Scale

Scratch

Mineral

hardness (Mohs)

used for comparison

1

Talc

2

Gypsum

3

Calcite

Simple hardness tester

resistance

(Rosiwal)

Can be scratched with fingernail Can be scratched with fingernail Can be scratched with copper coin

4

Fluorite

Easily

5

Apatite Orthoclase

Can be scratched with knife Can be scratched with steel file Scratches window glass

6 7

8 9 10

Quartz Topaz

Corundum Diamond

Cutting

scratched with knife

0.03 1.25 4.5 5.0 6.5

37 120 175 1,000

140,000

19

The Mohs' hardness scale is a relative hardness scale. It only shows which gemstone is harder than another one. Nothing is said about increase of hardness within the scale. is only possible with absolute hardness scales, for example, cutting resistance.

That

(See table, page 19.)

Hardness Test Formerly, when the optical examination methods had not been developed to such a degree as they are today, the scratch-hardness test played a larger role for the determination of gemstones. Now, the scratch-hardness test is used in general only for less valuable gemstones. Furthermore, it is too inaccurate for a precise testing of hardness, and there is the danger of hurting the gemstone. In the trade, test pieces and scratch tools for the testing of hardness can be bought. When doing the scratch test, one must make sure that the examination is done only with sharp-edged objects on fresh, nondecomposed crystal or cut surfaces. Corrugated or foliated formations feign a lesser hardness. Always begin with softer test materials in order not to damage the gemstone unnecessarily. If possible, do not scratch cut stones at all, but rather test only at an unnoticeable spot, or on the underside.

Cutting Resistance For the gemstone cutter, naturally the hardness of a stone, when cutting, plays an important role. There are also gemstones which are of a different hardness on different crystal faces and in different directions. For the stone collector, small differences in hardness are of lesser importance. In kyanite (compare drawing below and page 196), for example, the Mohs' hardness along the stem-like crystals is 4/2, but across it is 6 to 7. There are also large differences in hardness in diamond on the crystal faces (see drawing below). (For more about the cutting of diamond, see page 65.) For the gemstone cutter, it would be helpful to have absolute values regarding the cutting hardness of gemstones. Unfortunately, there are hardly any useful numbers available. The cutter must rather discover for himself in practice and rely on his experience. It is real art

to cut softer gemstones,

which only

a

few

specialists master. If the

crystal faces of a stone, in addition, are of different hardnesses,

form sharp and even edges on these

it

takes a lot of skill to

stones.

When polishing gemstones, the hardness is of utmost importance, because harder gemstones take

a polish better

than softer stones. Left: Differences in

hardness in diamond. The shorter the arrow, the larger the cutting hardness in this direction (according to E.M. and J. Wilks).

Right: Differences

hardness

in

Clearly different

hardnesses longitudinal

in

kyanite.

Mohs'

in

and

transverse directions.

20

f

Selected

Gemstones

Ordered by Moris' Hardness

Diamond

Corundum Ruby Sapphire Alexandrite Chrysoberyl

10 9 9 9 8/2 8V? 8/2

5-5/2 5-5/2 5-5/2

Sinalite

6'/2-7

Obsidian

Tansanite

6'/2-7

Titanite

Tiger's Eye

6V2-7

Wolframite

Galliant

6 1/2 6 1/2

Apatite Dioptase Eosphorite

5

Hemimorphite

5

Smithsonite

5

Vesuvian Epidote

5 5

Aventurinefeld

6-7 6-7 6-7 6-6 1/2 6-6 1/2 6-6 1/2

Benitoite

6-6/2

Scheelite

4/2-5 4/2-5 4/2-5

Fa bu lite

6-61/2

Colemanite

4/2

71/2-8

Labradorite

6-6 1/2

Kyanite

Precious beryl

71/2-8

Moonstone

Variscite

Gahnite Phenakite Emerald

71/2-8

Nephrite Orthoclase

4-7 4-5 4-5

Andalusite Euclase

71/2

Prehnite

71/2

Pyrite

Hambergite

71/2

Rutile

Sapphirine

71/2

Sugilite

Dumortierite

7-81/2 7-71/2

Tantalite

Boracite

6-6/2 6-6/2 6-6/2 6-6/2 6-6/2 6-6/2 6-6/2 6-6/2 6-6/2 6-6/2

Cordierite

7-71/2

Amblygonite

7-71/2

Sanidine

6 6

Azurite

Danburite Simpsonite Tourmaline

7-71/2

Amethyst

Rose quartz

7 7 7 7 7 7 7 7

Hematite Magnetite Opal Rhodonite

Almandine

6/2-7 1/2

Andradite

61/2-71/2

Sodalite

Demantoide

6 1/2-7 1/2

Tugtupite

5/2-6/2 5/2-6/2 5/2-6 5/2-6 5/2-6 5/2-6 5/2-6 5/2-6 5/2-6 5/2-6 5/2-6

Garnet

6V2-71/2

Brasilianite

5/2

Grossular

61/2-71/2

Enstatite

Hessonite Pyrope Spessartine Uvarovite

6/2-7/2

Linobate Moldavite

5/2 5/2 5/2 5/2 5/2

Zircon Djevalite

Taaffeite

8-8/2 8-8tt

Kassitente Pyrolusite

Amazonite Andesine

YAG

8 8 8

Aquamarine

7V2-8

Beryl

Spinel

Topaz

Aventurine

Rock Crystal Citrine Prasiolite

Quartz

Smoky quartz

71/2-8 71/2-8

7-71/2

61/2-7 1/2 61/2-7 1/2 61/2-7 1/2

Petalite

Zoisite

Aktinolite

Anatase Berylonite

Hauynite Leucite Periclase

Skapolite

Smaragdite

Zircon

6V2-7 1/2

Agate

61/2-7

Axinite

61/2-7

Willemite Cancrinite Charoite Diopside

Chalcedony Chrysopase

61/2-7

Hyperstene

61/2-7 61/2-7

Katapleite

Diaspore Hiddenite Jadeite

Jasper

Kornerupine Kunzite

6V2-7 6V2-7 61/2-7 61/2-7

Lapis Lazuli Lazulite

Tremolite Turquoise

Analcime

6/2-7

Datolite

Peridot

6 1/2-7

Melinophane

Pollucite

61/2-7

Natrolite

Strass

5

Apophylite Gaspeite

Zinkite

Sphalerite

4-4/2 4 4 4 4 3/2-4/2 3/2-4/2 3/2-4 3/2-4 3/2-4 3/2-4 3/2-4 3/2-4 3/2-4

Anhydrite

3/2

Coral

3-4

Barite

3-3/2 3-3/2 3-3/2 3-3/2 3-3/2

Purpurite

Ammolite Barytocalcite Fluorite

Rhodochrosite Magnesite Siderite

Aragonite Cuprite

5/2-6/2

Dolomite

5/2-61/2

Chalcopyrite Malachite

5-6 5-6 5-6 5-6 5-6 5-6 5-6 5-6 5-6 5-5/2 5-5/2 5-5/2 5-5/2

Cerussite Celestine

Howlite Witherite Calciate Kurnakovite

Wulfenite Serpentine

3 3 3

Silver

2/2-5/2 2/2-4/2 2/2-3 2/2-3 2/2-3 2/2-3

Pearls

Gaylussite

Gold Krokoite Proustite

2/2

Chrysokoll Phosgenite

2-4 2-3

Amber

Cinnabar

2-2/2 2-2/2 2-2/2 2-2/2

Gypsum

2

Sulphur

I/2-2/2

Stichite

1

1/2-2/2

Vivianite

1

1/7-2

Talcum

1

Meerschaum Ulexite

21

Cleavage

and Fracture Many gemstones Cleavage

is

can be

split

along certain

flat planes,

related to the lattice of the crystal

— the

which the expert

calls cleavage.

cohesive property of the atoms.

Depending on the ease with which a crystal can be cleaved, one differentiates between a perfect (euclase), a good (topaz), and an imperfect cleavage (garnet). Some gemstones cannot be cleaved at all (quartz). One then says, they do not have cleavage.

A loosening of contact twins

is

not called cleavage, but separation.

Lapidaries and stone setters must take account of the cleavage. Often a small tap or too much pressure when testing for Mohs' hardness is sufficient to split the stone.

When soldering, the temperature can cause fissures along the cleavage planes, where eventually the

gem may

break completely along this

line.

perfect cleavage are considered small artistic creations, in facets of such

stone could

Faceted gemstones with

demand by collectors. The

gemstones must be transverse to the cleavage planes, otherwise the apart like a leaf. Piercings should, if possible, be done vertically to the

fall

cleavage surfaces.

Cleavage is used to divide large gem crystals or remove faulty pieces. The largest diamond of gem quality ever found, the Cullinan of 3106cts, was cleaved in 1908 into three large pieces which were then cleaved into numerous smaller pieces. Today, small pieces are usually sawn in order to avoid unwanted cleavages, and to make the best use of the shape of the stone.

The

breaking of a gemstone with a blow producing irregular surfaces is called can be conchoidal (shell-like), uneven, smooth, fibrous, splintery, or grainy. Sometimes, the type of fracture helps to identify a mineral. Conchoidal fracture is, for instance, characteristic for all quartz and glass-like minerals.

fracture. It

Density

and

Specific Gravity

According to the new physical nomenclature, the measurement specific gravity, which indicates the weight of a specific material compared with the weight of the same volume of water, is now replaced by the term density. Weight is in fact not a constant attribute. It depends on the magnitude of the gravity at the respective location where it is measured. But for the determination of the weight of gemstones, this does not matter, since the measurement is always done under the same gravitational conditions. The density is a dimension independent of location. It is defined as substance per unit volume represented in g/cm 3 and/or kg/m 3 Density relates the gemstone to the same volume of water. In practice in the trade and in gemology, there is not a widespread distinction between using the term density and specific gravity, since nothing is really changed in actual measurement by the new nomenclature. Nevertheless, in the following, the term density is used instead of specific gravity In regards to the "heaviness" of a gemstone, we will continue to speak of "weight" and not of the "density" of a gemstone, since that corresponds to the practice of the gemstone trade. The density of gemstones varies between 1 and 8. Values under 2 are considered light (e.g., amber about 1), those from 2 to 4 normal (quartz 2.6) and those over 4 are .

22

a

considered heavy (kasscritc around 7). The more valuahle gemstones (such as di mond, ruhy, and sapphire) have densities that are much greater than the common rock-forming minerals, especially quartz and feldspar. Such heavy minerals are deposited in

flowing waters before the sands, which are rich (compare with page 53).

in quart/.,

and they form the so-

called placer deposits

Determination of Density In identifying gemstones, a determination of the density can be useful. But for

procedures for the determination of gemstones are more common. These procedures require expensive instruments, however. Two methods have proven a success for the determination of the density of gemstones: the buoyancy method with the help of a hydrostatic balance and the suspension, or heavy liquid, method. The first is time consuming, but inexpensive. Even though the second method is a little bit more expensive, it produces good results in a short time, especially with lots of unknown gems. However, the immersion liquids specialists, optical

are quite hazardous.

Hydrostatic Balance The measuring procedure with a hydrostatic scale works on Archimedes' Principle of buoyancy. The volume of the unknown gem is determined. The density is then easily worked out. A hydrostatic balance can be constructed by anybody (see illustration below). The beginner can adapt letter scales. Anyone more advanced should use a precision balance as used by a chemist or pharmacist. The object to be tested is first weighed in air (in the pan under the bridge) and then in water

(in the

net in the beaker).

Hydrostatic balance for determining

gemstone volume.

23

The

difference in weight corresponds to the weight of the displaced water and numbers to the volume of the gemstone. It is possible for the layman to

therefore in

determine the density with this method to one, and with practice, to two decimal places. It is important to ensure that the stone is not in contact with a foreign substance, that it is not set, and that, when weighed in air, it is dry.

Example: Substance (weight) in air 5.2 g Substance (weight) in water 3.3 g Difference

= Volume

1.9

cm

Density 3

Substance

5.2

Volume

1.9

=

2.7

g/cm

:

Suspension Method

This method rests on the idea that by definition an object remain suspended in a liquid of the same density; it will neither sink to the bottom nor float to the surface. The specimen is put into a liquid with a high density (heavy liquid). The liquid is diluted (lightened) — and the degree of dilution is recorded — until the specimen is suspended. The density of the heavy solution, which has been diluted, is done by specialists with a scale constructed for this purpose (Westphal

will

balance).

The gem

enthusiast

is

advised to use control indicators of known density, such as

When

such an indicator is suspended in the liquid, its of the liquid and thus of the test object. There are various heavy liquids available, but some are quite hazardous. The ones that can be thinned with distilled water are most suitable. One of these is Thoulet's solution (a potassium-mercury-iodine solution) with the density of 3.2. With it, about half of all gemstones can be identified. For heavier stones, one can use Clerici solution (a thallium-formate-thallium-malonate solution) with a density of 4.2. This density covers the entire field of gemstones with the exception of only about two dozen gemstones. But it is expensive and in addition very poisonous and acid; laymen should not use it. For a density up to 3.5, one can use Rohrbach's solution (a bariummercury-iodide solution). The thinned liquid need not be discarded; one can recover the original specific density by evaporation in a steam bath. All of these heavy liquids, however, are poisonous. Therefore, use them only with utmost caution. Do not breathe in vapors; do not eat while you are working. The suspension method is especially recommended, when certain gemstones are to be sorted out from a collection of unknown stones or when it is necessary to distinguish syntheses and imitations from genuine gemstones. pieces of glass or minerals.

density

is

by definition the same

Emerald

^

Tourmaline

as that

Dioptase

Determining the density of a gemstone with the help of heavy liquids (e.g., with the Thoulet's solution with a density of 3.20). Lighter stones float at the surface; heavier ones sink to the bottom. Gemstones with the same density as that of the liquid are suspended in the liquid.

24

Selected Gemstones

Ordered by Density

Gold Silver

Cinnabar Wolframite Galliant

Kasserite

Wulfenite Cerussite

Phosgenite Simpsonite Scheelite

7.05 6.7-7.1

Agirinaugite

Hyperstene

3.45-3.70 3.41-3.52 3.40-3.74 3.40-3.58 3.40-3.55 3.4-3.5

6.50-7.00 6.46-6.57

Tansanite

3.35

Rose quartz

Triphyline

Vesuvian Epidot

3.34-3.58 3.32-3.47 3.3-3.5 3.30-3.50 3.30-3.39 3.30-3.38 3.28-3.48 3.28-3.35 3.27-3.45 3.26-3.41 3.26-3.36 3.25-4.10 3.24-3.50 3.22-3.38 3.2-3.4 3.20-3.30 3.16-3.23 3.15-3.21 3.15-3.21

Vivianite

6.13

15.5-19.3 9.6-12.0 8.0-8.2 7.1-7.6

5.92-6.84 5.9-6.3

Rhodochrosite Uvarovite

Rhodonite Sapphirine

Hemimorphite

Krokoite Cuprite

5.9-6.1

Diaspor

5.85-6.15

Jadeite

Zinkite

5.66 5.6-5.7

Peridot

Djevialite

Proustite

Zirkon Tantalite

Hematite Fabulite Pyrite

Linobate

YAG

5.51-5.64 5.5-5.9 5.18-8.20 5.12-5.28 5.11-5.15 5.00-5.20 4.64-4.66

Pyrolusite

4.55 4.5-5.0

Davidite

4.5

Baryite

4.43-4.46 4.27-4.79 4.20-4.30 4.12-4.18 4.10-4.30 4.00-4.65 4.00-4.62 3.98-4.04 3.97-4.05 3.97-4.00 3.95-4.03 3.93-4.73 3.93-4.30 3.90-4.10 3.89-4.18 3.83-3.96

Witherite Rutile

Spessartine

Copper

pyrite

Smithsonite

Gahnite Legrandite

Ruby Celestine

Sapphire Zircon

Almandine Sphalerite

Willemite Siderite

Dioptas Kornerupine Dumortierite Axinite

Malachite

Smaragdite Diopside Purpurite Enstatite

Apatite Hiddenite Kunzite Euclase Andalusite Lazulite

Aktinolite

Amblygonite Fluorite

Melinophane Montebrasite Brasilianite

Danburite Tremolite

Phenakite Aragonite

Hornblende Nephrite

Anhydritspar

Periclase

3.7-4.1 3.7-3.9 3.7-3.9

Chrysoberyl

3.70-3.78

Tourmaline

Barytocalcite

3.66

Prehnite

Staurolite

3.65-3.77 3.64-3.68 3.63-3.79 3.62-3.87 3.60-3.62 3.57-3.73 3.54-3.63 3.53-3.70 3.52-3.54 3.50-3.53 3.49-3.57 3.46-3.50

Dolomitspar

Andradite Azurite

Benitoite Strontianite

Pyrope Taaffeite

Grossular Spinel

Kyanite Titanite

Diamond Topaz Sinhalite

Datolite Pollucite

Berylonite

Muskovite Sugilite

Ammolite Katapleite Calcite

Aquamarine Emerald Precious beryl Labradorite

Andesine

3.10

3.05-3.20 3.04-3.14 3.03-3.07 3.01-3.11 3.00-3.25 3.00-3.03 2.98-3.11 2.98-2.99 2.97-3.03 2.95-3.07 2.95-2.97 2.94 2.9-3.4

2.90-3.03 2.90-3.00 2.90-2.98 2.85-2.94 2.82-3.32 2.82-2.94 2.80-2.95 2.80-2.87 2.78-2.88 2.76-2.80 2.75-2.80 2.72 2.69-2.71

2.68-2.74 2.67-2.78 2.66-2.87 2.65-2.75 2.65-2.69

Amethyst Rock crystal Citrine Prasiolite

Quartz

Smoky

quartz

265 2.65 2.65 2.65 2.65 2.65 2.65

Leucite

2.64-2.70 2.64-2.69 2.62-2.65 2.60-2.85 2.60-2.70 2.60-2.64 2.58-2.91 2.58-2.91 2.58-2.66 2.58-2.64 2.58-2.64 2.58-2.64 2.58-2.64 2.57-2.74 2.56-2.59 2.56-2.58 2.55-2.80 2.54-2.78 2.50-3.00 2.45-2.58 2.45-2.50

Carletonite

2.45

Serpentine

Hauynite Colemanite

2.44-2.62 2.42-2.58 2.42-2.51 2.4-2.5 2.40-2.42

Aventurine Aventurine Fsp. Pearls

Coral

Agat Fossilized

wood

Jasper Cordierite

Chalcedony Chrysoprase

Moss agate Tiger's

eye

Skalpolite

Moonstone Amazonite Talc

Charoite Lapis lazuli

Howlite

Variscite

Cancrinite

Petalite

2.40

Tugtupite Obsidian

2.36-2.57 2.35-2.60

Hambergite

2.35

Moldavite Turquoise Apophyllite Mesolite

2.32-2.38 2.31-2.84 2.30-2.50 2.26-2.40 2.22-2.29 2.20-2.26 2.19-2.23 2.16-2.18 2.14-2.40 2.05-2.08 2.00-2.40

Analcime Natrolite

Yugavaralite Stichite

Sodalite

Sulphur Chrysokoll

Meerschaum Gaylussite

2.0-2.1 1.99

Opal Thaumasite

1.91

1.98-2.50

Kurnakovite

1.86

Ivory

1.7-2.0 1.65-1.95 1.19-1.35 1.05-1.09

Ulexite

Gagate

Amber

25

Weights Used in

the

Gem Trade

In the international

gem trade, the carat, gram, grain, and momme are used as units of

weight.

The weight used

Carat

in the

gem

trade since antiquity.

the seed (Jknara) of the African Coraltree or

The name

from the kernel (Greek

is

derived from

keration) of the

Carob bean. Since 1907 Europe, as well as America, has adopted the metric carat (met) of

200

mg

or 0.2

g.

location, varying

Local carat weights have differed historically from location to

between 188 and 213 mg.

The carat is subdivided into fractions (e.g., '/ioct) or decimals (e.g., 1.2 5ct) up to two decimal places. Small diamonds are weighted \npobits, which are V\aa carat (O.Olct). The table below illustrates diameter and corresponding carat weight for diamonds cut in the modern brilliant cut (see page 81). Gems with different density and different cuts obviously have different diameters.

The

price of a

gemstone

is

always indicated in the

gem

trade "per carat."

calculating the actual weight, one receives the price per piece.

When

By

selling to the

though, usually the total price is given. The carat price progressively gemstone in very small increments. When a one-carat piece, for example, costs $750, then a two-carat-piece is not necessarily worth $1500, but maybe $3000 or even more. The carat weight of gems is not to be confused with the carat used by the goldsmith. In the case of gold the carat is not a weight measure at all but rather a measure of quality. The higher the caratage, the higher the content of gold in the piece of jewelry. The weight can be variable. final buyer,

increases with the size of the

Gram

The

especially for

Grain Today,

weight measure used in the trade for rough stones.

less

precious gemstones and

Formerly, the weight measure for pearls. It corresponds to 0.05g or increasingly substituted by use of the carat.

Momme

The

old Japanese measure of

momme = 3.75g= 18.75ct) (

anymore

Diameters and Weights of

Brilliant

Diamonds

© Diameter in mm Weight in carat

74 1

26

'Act.'

it is

50

2.2

3.0

4.1

5.2

1/25

0.10

0.25

0.50

9.0 2

50

9.3

3.00

is

hardly used

Optical

Properties Of all

the various properties of gemstones, the optical characteristics are of unsur-

They produce color and luster, fire and luminescence, play of and schiller (iridescence). In the examination of gems, nowadays, there is more and more concentration on the optical effects. passed importance. light,

Color Color

most important characteristic of gems. In the case of most stones, it is not many have the same color and numerous stones occur in many colors. Color is produced by light; light is an electromagnetic vibration at certain wavelengths. The human eye can only perceive wavelengths between 750 and 380 nm (see page 35). This visible field is divided into several sectors of certain is

the

diagnostic in identification, because

wavelengths, each of a particular color (spectral colors: red, orange, yellow, green, blue, violet).

Crystal step with amethyst;

Mexico (somewhat reduced).

The mixture of all these colors produces white light. If, however, a certain wavelength (i.e., also the corresponding color) is absorbed out of the entire spectrum, the remaining mixture produces a certain color, but not white. If all wavelengths pass through the stone, it appears colorless. If all light is absorbed, the stone appears black. If all wavelengths are absorbed to the same degree, the stone is dull white or gray. In the case of gemstones, the metals and their combinations, especially chrome, iron, cobalt, copper, manganese, nickel, and vanadium, absorb certain wavelengths of light and so cause coloration. In the case of zircon and smoky quartz, no impurity, or foreign substance, is responsible for the color, but rather a deformation of the internal crystal structure (lattice) results in the selective absorption of light, giving a change in the original color.

27

The and thus

distance the light ray travels through the stone can also influence absorption color.

The cutter must therefore use this fact to his advantage. Light-colored

made

thicker and/or are given such an arrangement of facets that the absorption path lengthens, giving a deeper color. Materials with colors that are too dark are cut thinly. The dark red almandine garnet, for example, is therefore often hollowed out on the underside.

stones are

an influence on the color of gemstones, as it is usually differcomposed than daylight. There are gemstones whose color is influenced unfavorably by artificial light (e.g., sapphire), and those which have an especially radiating effect in artificial light (e.g., ruby and emerald). The most obvious change in color occurs in alexandrite, which is green in daylight and red in artificial light. Although color is of great importance in gems, with the exception of diamonds, no practical method of objective color determination is known. Color comparison charts Artificial light has

ently

poor substitutes because there is too much room for subjective consideration. The measuring methods used in science for color determination are too complicated for are

the trade.

Color of Streak

The color appearance of gems, even in the same group, can vary greatly. For instance, beryl can have ness

is,

all

the colors of the spectrum, but can also be colorless. This colorless-

in fact, the true color. It

is

called inherent color. All other colors are

produced by

impurities.

The inherent color, as it is constant, can help to identify a stone. This color can be seen by streaking the mineral on a rough porcelain plate, called the streak plate. The finely ground powder has the same effect as thin transparent platelets, from which the color-producing impurities have been abstracted. Steely hematite, for instance, has a streak color (called streak) which is red. Brass-colored pyrite's streak is black, and blue sodalite's little

is

white. In the case of very hard gemstones,

powder with

a steel

file,

and then rub

it

on the

it is

advisable

first

remove a method of

to

streak plate. This

determination is of special interest to collectors. Because of the danger of damage, cut gem should not be tested for streak. Refer to the table of streaks on page 30.

a

Color Change

The

color of

some gems

is

altered

by time. Amethyst, rose quartz, and kunzite can

when exposed to direct sunlight. Generally color changes effected by natural causes are not common. Much more frequently man uses scientific methods to become

paler

enhance the color of certain gemstones. Best known is the heat treatment "firing" of amethyst. At several hundred degrees, the original violet stone becomes light yellow, red-brown, green, or milky white. Most citrines on sale and all prasiolites are amethysts whose color has been changed this way. Less attractive colors can be changed to more desirable hues by heating. Greenish aquamarines are heated to a sea-blue color; tourmalines which are too dark can be lightened; and blue tourmalines can be turned green. Diamond-like and aquamarine-colored zircons are produced by heating the red-brown hyacinth variety. Colors can also be improved by radium and X-ray treatment and, more recently, by bombardment with elementary particles. The resulting colors are usually so close to nature that they cannot be detected by the eye; complicated tests are required to unmask them. Some of these resulting colors are not permanent; the stones can

28

Opal

in

matrix, so-called boulder opal; Queensland, Australia (about natural

become lazuli, oils,

pale,

change

color, or

become

spotty. In case of

turquoise, pearls, and agate, colors are improved

and wax. Such stone dyeing

is

a

size).

porous gems, such

as lapis

by the addition of pigments,

very ancient practice.

Requirements for the Trade In the trade, all artificially caused color changes of gemstones must be marked as such according to the guidelines of the CIBJO, with the exception of the following: those "which have received through heat treatment a permanent and irreversible color change" from the list "amber, beryl (aquamarine, morganite),

corundum

(sapphire, ruby), quartz (citrine, prasiolite, amethyst), topaz

(rose topaz), tourmaline

(all

colors), zoisite (blue tansanite)"; also in the case of those

"which through heat treatment and through the influence of acid and corrosive mordant have received a permanent and irreversible change in color, such as banded agate, cornelian, onyx, green agate, and blue agate." These specific exceptions do not require the indication of artificial coloration in the trade.

29

Selected Gemstones

Ordered by Streak

White, colorless, gray

Gaylussite

Silver

Fergusonite

Glass Grossular

Sinhalite

Agate

Hambergite

Actinolite

Hauynite

Smithsonite Smoky quartz

Gagate Gold Hubemite

Alabaster Alexandrite

Hemimorphite

Sodalite

Rutile

Spessartine

Sulphur

Almandine Amazonite

Hessonite Hiddenite Howlite

Spinel

Sphalerite

Spodumene

Stibiotantalite

Amber

Hyperstene

Staurolite

Thorianite Tiger's

Amblygonite Amethyst Amethyst quartz Anatase

Skapolite

Neptunite

Ivory

Strass

Jadeite

Tansanite

Jasper

Titanite

Eye Vanadinite Wurtzite

Kassiterite

Topaz

Zinkite

Andalusite Andradite Anhydrite Apatite Aphphyllite

Kornerupine Kunzite Kurnakovite

Tremolite

Aquamarine

Lazulite

Uvavorite

Aragonite Augelite Aventurine Aventurine feldspar

Leucite

Variscite

Linobate

Axinite

Milarite

Vesuvian Willemite Witherite Wulfenite

Barite

YAG

Benitoite

Mimetesite Moldavite Monazite

Beryllonite

Moonstone

Zoisite

Brazilianite

Calcite

Montebrasite Moss agate

Cancrinite

Natrolite

Cerussite

Chalcedony

Nephrite Obsisian

Charoite Chrysoberyl

Opal Orthoclase

Chrysoprase

Parisite

Citrine

Peridot

Celestine

Periclase

Colemanite

Peristerite

Coral

Pearl

Cordierite

Petalite

Cornelian Danburite

Phenacite Phosgenite

Datolite

Prasiolite

Demantoid Diamond

Precious beryl

Barytocalcite

Diopside Djevalite

Dolomite Dumortierite

Emerald Enstatite

Kyanite Labradorite

Magnesite

Meerschaum

Prehnite

Pyrope Quartz Rhodochrosite Rhodonite Rock crystal Rose quartz

Turquoise Tugtupite Tourmaline Ulexite

Zircon Zirconia

Green, yellow-green, blue-green Bayldonite

Chrysocolla Dioptase Gadolinite Gaspereite

Hornblende Malachite Marcasite

Blue, blue-green,

blue-red

Red, pink,

Azurite

orange

Boleite

Cinnabar

Cerulite

Cuprite

Euzenite

Friedelite

Lapis lazuli

Greenockite Hematite Krokoite Manganotantalite Piemontite

Linarite

Shattuckite Vivianite

Proustite

Purpurite Pyrargyrite

Pyroxmangite Realgar

Black, gray Anthophylite Aschynite Bixbite

Chalcopyrite Davidite llmenite llvaite

Ruby

Yellow,

orange,

Magnetite Melonite

Fabulite

Sanidine Sapphire

brown

Pyrite

Fluorite

Scheelite

Chromite

Pyrolusite

Gahnite

Serpentine

Descloizite

Tantalite

Galliant

Siderite

Durangite

Wolframite

Epidote Euclase

30

Refraction of Light

Most of us, when

when

was partially immersed in water The lower part of the stick appeared to be at a different angle from the upper part. What we observed was caused by the refraction of light. It always occurs when a ray of light leaves one medium (for instance, air) and enters obliquely into another (for instance, water and/or a gem crystal) at the interface between the two media. at a slant,

it

children, noticed that

appeared to "break"

water

at

a stick

level.

The amount of refraction in the crystals is constant for each specific gemstone. It can therefore be used in the identification of the type of stone. The amount of the refraction is called the refractive index and is defined as the proportional relation between the speed of light in air to that in the stone. A decrease in the velocity of light of the light

in the stone causes a deviation

Example:

rays.

Speed of light in air (V,) Speed of light in diamond (V2 ) Refractive index

V

=

V

2

l

(air)

(diamond)

300 000 km/sec 124 120 km/sec

=

300 000

=

2.417

124 120

This means that the speed of light in air is 2.4 times faster than the speed of light in diamond. The refractive indices of gems are betwen 1.4 and 3.2 They vary somewhat with color and occurence. Doubly refractive gems (see the descriptions on page 34) have two refractive indices. (Also refer to the refractive indices chart on pages 32 and 33.) .

Diagram of a refractometer as

commonly

used

in

the

trade, with inset of

refractometer scale.

Refractometer The light refraction is measured in practice with a refractometer. The values can be read directly from a scale. However, testing is only possible up to a

on a common instrument, and only stones with a flat face or facet are The determination of the refractive indices of other stones and of values over

value of 1.81 suitable. 1.81

requires the use of special devices.

The expert can find approximate values of cabachons using his own experience and knowledge.

31

Refractive Indices for Selected

and Double Refraction

Gemstones Refractive

Double

Index

Refraction

Refrad ive Index

Double

none 0.015-0.049 0.108-0.110 none 0.022-0.026 0.004-0.009 0.010-0.014 none none 0.015-0.033 0.048-0.050 0.048

Triphyline

1.730- -1.757 1.729- -1.768 1.720- -1.848 1.720- -1.756 1.719- -1.748 1.719- -1.730 1.716--1.752 1.715- -1.754 1.712--1.762 1.710- -1.734 1.708- -1.760 1.702- -1.750 1.701--1.743 1.701- -1.734 1.700- -1.800 1.700--1.723 1.691- -1.700 1.690- -1.736 1.690- -1.723 1.690 1.689- -1.702

Lithiophilite

1.68- .70

0.01

Dumortierite Legrandite

1.678- -1.689 1.675- -1.740 1.673- -1.731 1.671- -1.772 1.670- -1.734 1.665- -1.712 1.665- -1.686 1 .664- -1.730 1.662- -1.707 1.660- -1.699 1.660- -1.681 1.660--1.681 1.658- -1.673 1.656- -1.704 1.655- -1.909 1.652--1.688 1.650- -1.703 1.650- -1.697 1.650- -1.680 1.650- -1.677 1.650- -1.670 1.644- -1.709 1 .640- -1.680 1.638- -1.671 1.637- -1.681 1.637- -1.653 1.636- -1.648 1.634- -1.685 1.633--1.875 1.630- -1.636 1.629- -1.674 1.628--1.649

0.015-0.037

Hessonite Epidote Azurite Pyrope Hodgkinsonite

Pyrargyrite

2.940-3.220 2.905-3.256 2.881-3.084 2.88-3.08

Cuprite

2.849

none

Rutile

0.287 0.117 0.046- 0.067

Taaffeite

none none

Spinel

0.080 none 0.270 0.120 0.160

Adamine

Hematite Cinnabar Prousite

Diamond

2.616-2.903 2.583-2.700 2.488-2.564 2.417-2.419

Fabulite

2.409

Stibiotantalite

2.370-2.450 2.368-2.371 2.29-2.66 2.280-2.400 2.26-2.43 2.202-2.273 2.19-2.34

Brookite

Anatase

Sphalerite

Krokoite Wulfenite Tantalite

Linobate

Mangano-

0.287 0.351 0.203 0.200

Mimetesite Phosgenite Zirconia

Senarmontite Galliant Zinkite Kassiterite

Simpsonite Sulphur Bayldonite Scheelite

Andradite Anglesite Uvarovite Purpurite Titanite

YAG Zircon

Cerussite

Gahnite Spessartine Painite

Almandine Gadolinite

Ruby Sapphire Benitoite

Shattuckite

Chrysoberyl Periclase

Skorodite Staurolite

Grossular

Pyroxmangite Chambersite

32

Kyanite

Diaspore Serendibite Sapphirine Agirinaugite

0.071

Vesuviane

0.150

Tansanite

tantalite

Djevalite

Rhodonite Gahnospinel

2.172-2.182 none 2.120-2.135 0.015 2.114-2.145 0.028 2.088-2.176 none 2.087 none 2.03 none 2.013-2.029 0.016 1.997-2.098 0.096- -0.098 1.976-2.034 0.058 1.958-2.245 0.291 1.95-1.99 0.040 1.918-1.937 0.010- -0.018 1.88-1.94 none 1.878-1.895 0.017 1.87 none 1.85-1.92 0.007 1.843-2.110 0.100- -0.192 none 1.833 1.810-2.024 0.002- -0.059 1.804-2.079 0.274 1.791-1.818 none 1.790-1.820 none 1.787-1.816 0.029 1.770-1.820 none 1.77-1.82 0.01-0.04 1.762-1.778 0.008 1.762-1.778 0.008 1.757-1.804 0.047 1.752-1.815 0.063 1.746-1.763 0.007- -0.011 1.74 none 1.738-1.768 0.027- -0.030 1.736-1.762 0.010- -0.015 1.734-1.759 none 1.734-1.756 0.017- -0.019 1.732-1.745 0.010

Neptunite Willemite Rhodozite

Hyperstene Parisite

Klinozoisite Sinhalite

Lawsonite Diopside Bustamite Kornerupine Hiddenite Kunzite Boracite Axinite

Malachite Jadeite

Peridot

Ludlamite Entatite

Euclase Phenakite Dioptase

Gagate Eosphorite Spurrite

Jeremejewite Barite

Durangite Siderite

Danburite Klinohumite Apatite

Refraction

0.005

0.004-0.007 0.030-0.050 0.002-0.012 0.009

0.029-0.045 0.028-0.033 none 0.006-0.008

0.060

0.010-0.016 0.081-0.101 0.005-0.015 0.036-0.042 0.019-0.021 0.024-0.031 0.014-0.015 0.012-0.017 0.014-0.016 0.014-0.016 0.010-0.011 0.010-0.012 0.254 0.020 0.036-0.038 0.038-0.044 0.009-0.012 0.019-0.025 0.016 0.051-0.053 none 0.028-0.035 0.039-0.040 0.007-0.013 0.012 0.051 0.242

0.006-0.008 0.028-0.041 0.002-0.006

Andalusite Friedelite

Smithsonite Datolite

Celestine

Tourmaline Aktinolite

Hemimorphite Lazulite

Prehnite

Turquoise

Topaz Sugilite

Sogdianite Brasilianite

Rhodochrosite Odontolite Nephrite Pektolite

Montebrasite Phosphophyllite

Melinophane Eudialite

Chondrodite Katapleite

Wardite Ekanite

Herderite

Colemanite Howlite Zektzerite

Amblygonite Anhydritspar Augelite Emerald

Aquamarine Variscite

Precious beryl

Tremolite Vivianite

Serpentine Labradorite

Hambergite Beryllonite

Charoite

Amethyst Aventurine Rock Crystal Citrine Prasiolite

Smoky quartz Rose quartz Andesine Cordierite

Oligoclase Talc

Skapolite

Amethyst quartz

Refractive

Double

Refractive

Double

Index

Refraction

Index

Refraction

1.627-1.649 0.007-0.013 1.625-1.664 0.030 1.621-1.849 0.228 1.621-1 .675 0040 0.050 0.010-0.012 1 619-1.635 1.614-1.666 0.014-0032 1.614-1.653 0.020-0.025 1.614-1.636 0.022 1.612-1.646 0.031 0.036 1.61 1-1.669 0.021-0.039 1.610-1.650 0.040 1.609-1.643 0.008-0.016 1.607-1.611 0.001-0.004 1.606-1.608 0.002 1.602-1.623 0.019-0.021 1.600-1.820 0.208-0.220 1.60-1.64 0.010 1.600-1.627 0.027 1.595-1.645 0.038 1.594-1.633 0.22 1.594-1.621 0.021-0.033 1.593-1.612 0.019 1.591-1.633 0.003-0.010 1.59-1.64 0.035 1.590-1.629 0.039 1.590-1.599 0.009 1.590-1.596 0.001 1.587-1.627 0.023-0.032 1.586-1.615 0.028-0.030 1.586-1.605 0.019 1.582-1.585 0.003 1.578-1.646 0.024-0.030 1.570-1.614 0.044 1.570-1.590 0.014-0.020 1.565-1.602 0.006 1.564-1.596 0.004-0.005 1.563-1.594 0.031 1.562-1.602 0.004-0.010 1.560-1.643 0.017-0.027 1.560-1.640 0.050-0.075 1.560-1.571 0.008-0.014 1.559-1.570 0.008-0.010 1.553-1.628 0.072 1.552-1.561 0.009 1.550-1.561 0.004-0.009 1.544-1.553 0.009 1.544-1.553 0.009 1.544-1.553 0.009 1.544-1.553 0.009 1.544-1.553 0.009 1.544-1.553 0.009 1.544-1.553 0.009 1.543-1.551 0.008 1.542-1.578 0.008-0.012 1.542-1.549 0.007 1.54-1.59 0.050 1.540-1.579 0.006-0.037 1.54-1.55 0.009

1.54

none

Jasper

1.54

Amber

1.539-1.545 1.535-1.570 1.535-1.537 1.534-1.540 1.53-1.69 1.530-1.685 1.530-1.540 1.530-1.540 1.530-1.540 1.530-1.540

none none none

Fossilized

wood

Ivory

Apophylltte Tiger's

Eye

Pearls

Aragonite

Agate Chalcedony Chrysoprase Moss Agate

Meerschaum Withente Milarite

Nepheline Aventurine

0.002

none 0.16 0.155

004 0.009 0.004 0.009 0004 0.009 0.004 0.009 1.53 none 1.529-1.677 0.148 1.529-1.551 0.003 1.526-1.546 0.0004 1.525-1.548 0.010 \

feldspar

Amazonite Ammolite

Petal ite

1.522-1.530 1.52-1.68 1.52-1.67 1.520-1.529 1.518-1.530 1.518-1.526 1.517-1.525 1.516-1.544 1.515-1.542 1.509-1.717 1.509-1.525 1.504-1.509 1.504-1.508 1.502-1.698 1.502-1.519

Lapis lazuli

1.50

Strontianite

Gypsum Sanidine

Moonstone Pollucite Stichtite

Thomsonite Magnesite Skolezite

Leucite

Mesolite

Dolomite

Hauynite Tugtupite Cancrinite Celluloid Ulexite

Moldavite Yugawaralite Whewellite Kurnakovite Inderite

Calcite

Coral Nathrolite

Sodalite

Analcime Thaumasite Creed ite Chrysokoll Obsidian Gaylussite Glass Fluorite Sellaite

Opal

0.008 0.155 0.150 0.009 0.008 0.008

none 0.026 0.006- -0.025 0.022 0.007- -0.012 none 0.001

0.185 0.012- -0.017

none 1.496-1.510 none 1.496-1.502 0.006 1.495-1.528 0.024- -0.029 1.495-1.520 none 1.491-1.520 0.029 1.49-1.51 none 1.490-1.509 0.011- -0.014 1.489-1.651 0.159- -0.163 1.488-1.525 0.036 1.488-1.515 0.017- -0.027 1.486-1.658 0.172 1.486-1.658 0.172 1.480-1.493 0.013 1.48 none 1.479-1.489 none 1.464-1.507 0.036 1.461-1.485 0.024 1.460-1.570 0.023- -0.040 1.45-1.55 none 1.443-1.523 0.080 1.44-1.90 none 1.434 none 1.378-1.390 0.010- -0.012 1.37-1.52 none

33

Gemstones

in

an immersion

liquid.

1. White contour and dark facet edges: lower refractive index.

Black contour and white. facet edges: higher refractive index.

2.

3.

Widened contour:

gem

has

gem

has

refractive indices vary

considerably.

(tending to disappear): liquid

4. Indistinct outline

and

gem have same

refractive index.

(According to Dragstedt et

Immersion Method

al.)

Without access

to a costly apparatus, a rough measurement of easy with the immersion method. The gem is viewed after immersing in a liquid with a known refractive index. On the basis of brightness, sharpness, and width of the contours/outlines as well as the facet edges, one can learn

the refractive index

is

fairly

approximate values about the refractive index.

Double Refraction gemstones, except opals, glasses, and those belonging to the cubic system, the is refracted when entering the crystal and at the same time divided into two rays. This phenomenon is called double refraction. It can be most clearly observed in the case of calcite. It is also easily seen in zircon, titanite, tourmaline, and peridot. When looking from above, one can see the doubling of the edges of the lower facets in transparent cut stones. It is up to the lapidary to work the stone in such a way that the double refraction does not appear disturbing. The double refraction can be useful in identifying gemstones. It is expressed as the difference between the highest and lowest refractive index. The expert also differentiates between positive and negative "optical character". (Refer to the table on pages 32 and 33.) In

all

ray of light

Calcite

34

shows double

refraction especially clearly

(left),

and diagram of double

refraction (right).

Dispersion of the original white light when going through a prism, a

breakdown

into spectral

colors

Dispersion In colorless and cut gemstones, one can occasionally observe a play of color, which comes about through dispersion of the white light into the spectral colors. That is to say,

the white light

dispersed into

its

is

not only refracted when penetrating

spectral colors, because each wavelength

is

a crystal,

but

it

is

also

refracted by a different

amount. Violet is refracted more strongly than red. The dispersion is different from one gemstone to another. A distinct dispersion occurs only in colorless or weakly tinted stones. Facets can enhance the dispersion. Colorful gemstones tend to mask the dispersion effect.

diamonds where it produces a beautiful play Natural as well as synthetic gemstones with high dispersion (for instance, fabulite, rutile, sphalerite, titanite, and zircon) are used as substitutes for diamond; sometimes, though, they are supposititious (see page 75). The measurement of the dispersion is done with a refractometer and special devices. The dispersion of a stone is expressed in figures as the difference between the red and violet refractive indices. As the color usually comprises a wide spectrum, it is common to use certain lines (Fraunhofer lines) of the spectrum when doing the measurements. In the gemological literature, mainly the Fraunhofer lines B and G (BG dispersion) are used as a basis for the dispersion values, but occasionally the lines C and F (CF dispersion) are used. Tables of dispersion values can be consulted for the determination of the gemColor dispersion

of color, the so-called

stone. In the table

the

CF dispersion.

is

especially high in

fire.

on page

BG dispersion values are contrasted with those of CF dispersion following the BG values.

36, the

In the description of the individual gemstones, the

values are placed in brackets

Spectrum of the Fraunhofer

lines.

Dispersion refers either to the

BG

or the

CF

area.

35

Dispersion

of Selected Gemstones

B-G

B-G

C-F

Rutile

0.280

0.120-0.1:

Skapolite

Anatase

0.213- -0.259 0.203 0.19

0.133 0.109 0.088 0.075 0.035 0.035 0.035

Tourmaline Andalusite

Wulfenite Fabulite

Spodumene

Linobat

0.156 0.120

Kassiterite

0.071

Zirconia

Cerussite

0.065 0.062 0.057 0.057 0.055

Titanite

0.051

0.033-0.050 0.019-0.038

Benitoite

0.026 0.025 0.025

Sphalerite

Djevalite

Andradite

Demantoid

Diamond

0.046 0.044 0.044

Obsidian

0.041

Zircon

0.039 0.038 0.038 0.036 0.034 0.033 0.030 0.030 0.028 0.027 0.027 0.027 0.027 0.024 0.023 0.022 0.020 0.020 0.020 0.020 0.020 0.019 -0.025 0.019 0.019 0.018 -0.020 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.017 -0.020 0.017 0.017 0.017 0.017 0.017

Anglesite

Galliant

Scheelite

Dioptase

Whewellite

Gypsum Epidot Tansanite

YAG Almandine Hessonite Spessartine

Willemite Boracite Staurolite

Pyrope Grossular

Hemimorphite Kyanite Peridot Spinel

Vesuvian Klinozoisite

Labradorite Axinite

Ekanite

Kornerupine

Corundum Ruby Sapphire Sinhalite

Sodalite

Diopside Cordierite

Danburite Herdente Hiddenite Kunzite

Barite

Datolite

Euclase

Chrysoberyl

Hambergite Phenakite Rhodochrosite Sillimanite

Smithsonite

Amblygonite Aguamarine Brasiliantie

Precious beryl

0.022 0.022 0.026

Emerald Topaz

0.021

Amethyst guartz Apatite Aventurine

0.008 0.012-0.027 0.011

Amethyst

Rock

crystal

Citrine

0.015

Prasiolite

0.013-0.016

Quartz

Smoky guartz 0.015

Rose guartz Feldspar

0.012

Moonstone

0.012-0.013 0.013-0.016

Pollucite

Berylonite

0.012 0.013 0.011

Cancrinite

0.012-0.013

Calcite

0.011

Fluorite

Leucite Strontianite

0.017 0.017 0.017 0.016 0.016 0.016 0.016 0.015 0.015 0.015 0.015 0.015 0.014-0.031

C-F

0.010 0.009-0.011 0.009 0.009 0.009 0.011

0.009-0.010 0.009

0.010-0.020

0.008-0.017 0.014-0.015 0.008 0.009-0.013 0.014 0.008 0.014^ 0.009-0.013 0.014 0.009-0.013 0.014 0.014 0.008 0.013 0.008 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.012 0.012 0.012 0.010 0.010 0.010

0.008 0.010 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.007 0.007 0.008-0.009 0.008

0.008-0.028 0.008-0.017 0.013-0.014 0.007 0.004

0.014

0.011-0.014 0.010 0.011

0.012 0.010 0.011 0.011 0.011 0.010 0.009 0.012 0.009 0.009

0.008-0.009 0.010 0.010

Aragonite

0.500 0.019-0.021 0.014-0.021 0.013 0.010 0.010-0.011 0.009 0.009 0.008 0.008 0.008 0.008 0.007-0.012

Tremolite

0.006-0.007

Hematite Gahnite Uvarovite

Dolomitespar Enstatite

Phosphophyllite Aktinolite

Jeremejewite Apophylite Celestine

Hauynite Natrolite

36

,

Absorption Spectra absorption spectrum of a gem is one of the most important aids in identifying it. The absorption spectrum of a stone consists of the bands that appear in the spectral colors of light as they emerged from the gemstone (see page 40). As we can see, certain

The

wavelengths (color hands)

of the light are

absorbed (see page 27) and the color

of the

gem is formed from the mixture of the remaining parts of the original white light. The human eye cannot recognize all minute color differences. Red tourmaline, for instance, can

appear

like the desirable

like red garnet,

red ruby.

I

or even red-colored glass can appear deceivingly

lowever, the absorption spectrum unmasks without any

doubt the stone or glass used to imitate the ruby. Most gems have a very characteristic, even unique absorption spectrum which is revealed (seen through a spectroscope) in black vertical lines or broad bands. The great advantage of this testing method is the ease with which one can differentiate between gems of the same density and similar refractive index. One can also use this method for testing rough stones, cabochons, and even set stones. An important area where absorption spectroscopy is applied is in differentiating between natural stones, synthetic stones, and imitations. Best results are obtained from strongly colored, transparent gemstones. The observation of the absorption spectrum of opaque stones is only possible when a very thin slice of the stone is prepared which can transmit light. Otherwise translucent edge must be presented, or light must be reflected from the surface.

The testing instrument is the spectroscope, with the help of which one can determine the wavelength of the absorbed light. The wavelength is measured in ~ = 1 millionth millimeter). The former nanometers, symbol nm (lnm = 10 9 = 0.1 nm) is still widely used in the measurement Angstrom, symbol A (1 A = 10 _10 gemological literature. Because the absorption lines or bands are not always of equal strength, it is usual to note such measured differences. Strong absorption lines are in this book underlined, for instance, 653 medium strong absorption lines are in normal

m

m

;

lettering, for instance 594;

weak lines

are bracketed, for instance (432). (See the table

of the absorption spectra of selected gemstones

Hand spectroscope with wavelength

scale

in

on pages 38 and

39.)

the small tube.

37

Absorption Spectra of Selected Gemstones All figures

are

in

nanometers (nm).

Strong absorption

lines are

underlined;

weak ones

are

in

parentheses.

431 dyed green: 700, (665), (634) Alexandrite, green direction: 680, 678, 665, 655, 649, 645, 640-555 Alexandrite, red direction: 680, 678, 655, 645, 605-540, (472) Almandine: 617, 576, 526, 505, 476, 462, 438, 428, 404, 393 Amethyst: (550-520) Andalusite: 553, 550, 547, (525), (518), (495), 455, 447, 436 Andradite: 701, 693, 640, 622, 443

Actinolite: 503,

Agate,

artificially

Apatite, blue: 5J2, 507, 491, 464 Apatite, yellow-green: 597, 585, 577, 533, 529, 527, 525, 521, 514,

469

Aquamarine: 537 456, 427 Maxixe-Aquamarine: 695, 655, 628, 615, 581, 550 ,

Aventurine, green: 682, 649 Axinite: 532, 512, 492, 466, 440, 415 Azurite:

500

Bowenite: 492, 464 Calcite:

582

Chalcedony, artificially dyed blue: 690-660, 627 Chalcedony, artifically dyed green: 705, 670, 645 Chrysoberyl: 504, (495), 485, 445 Chrysoprase, artificially dyed with nickel: 632, 444 Chrysoprase, natural: 444 Cordierite: 645, 593, 585, 535, 492, 456, 436, 426 Danburite: 590, 586, 585, 584, 583, 582, 580, 578, 573, 571, 568, 566, 564 Demantoid: 701, 693, 640, 622, 443 Diamond, artificially dyed brown: (741), 594, 504, 498, 478, 465, 451, 435, 423, 415 Diamond, artificially dyed green: 741, 504, 498, 465, 451, 435, 423, 415 Diamond, artificially dyed yellow: 594, 504, 498, (478), (415) Diamond, natural brown-green: (537), 504 (498) Diamond, natural colorless to yellow (Cape): 478, 465, 451, 435, 423, 415, 401, 390 Diamond, natural yellow-brown: 576, 569, 564, 558, 550, 548, 523, 493, 480, 460 Diopside: (505), (493), (446) Chrome Diopside: (690), (670), (655), (635), 508, 505, 490 Dioptase: 550, 465 Ekanite: 665, (637) Emerald, natural: 683, 681, 662, 646, 637, (606), (594), 630-580, 477, 472 Emerald, synthetic: 683, 680, 662, 646, 637, 630-580, 606, 594, 477, 472, 430 Enstatite: 547, 509, 505, 502, 483, 459, 449 Chrome-Enstatite: 688, 669, 506 Epidote: 475, 455, 435 Euclase: 706, 704, 650, 639, 468, 455 Fluorite, green: 634, 610, 582, 445, 427 Fluorite, yellow: 545, 515, 490, 470, 452 Gahnite: 632, 592, 577, 552, 508, 480, 459, 443, 433 Grossular: 697, 630, 605, 505 Hematite: (700), (640), (595), (570), (480), (450), (425), (400) Hessonite: 547, 490, 454, 435 Hiddenite: 690, 686, 669, 646, 620, 437, 433 Hyperstene: 551, 547, 505, 482, 448 Jadeite, artificially dyed green: 665, 655, 645 Jadeite, natural green: 691, 655, 630, (495), 450, 437, 433 Kornerupine: 540, 503, 463, 446, 430 Kyanite: (706), (689), (671), (652), 446, 433 Nephrite: (689), 509, 490, 460 Obsidian, green: 680, 670, 660, 650, 635, 595, 555, 500 ,

38

Opal

700 640, 590 400 420 495, 493, 473, 453

(fire-opal):

Orthoclase: 448, Peridot: 497, Petalite:

(454)

705-685, 645, 625, 605, (587)

Precious Beryl, artificially dyed blue: Prehnite:

438

Pyrope: 68Z, 685, 671, 650, 620-520. Quartz, synthetic blue: 645, 585, 540, Rhodochrosite: 551, 449, 415 Rhodonite: 548, 503, 455, (412), (408)

505

500-490

Ruby: 694, 693, 668, 659, 610-500, 4Z6, 468, 465 Sapphire, blue from Australia: 471 Sapphire, blue from

Scapolite, pink: 663, Scheelite:

460 450 ,

460-450

Sapphire, green: 471, Sapphire, yellow: 471

,

Lanka: (450)

Sri

,

460 450 ,

652

584

462, 441, 410 526, 492, 475, 463, 452 Spessartine: 495, 485, 462, 432, 424, 412 Sphalerite: 690, 667, 651 Spinel, natural blue: 632, 585, 555, 508, 4Z8, 458, 443, 433 Spinel, natural red: 685, 684, 6Z5, 665, 656, 650, 642, 632, 595-490. 465, Spinel, synthetic blue: 634, 580, 544, 485, 449 Spinel, synthetic cobalt blue: 635, 580, 540, (478) Spinel, synthetic green: 620, 580, 570, 550, 540 Spinel, synthetic yellow-green: 490, 445, 422 Taaffeite: 558, 553, 478 Tansanite: 595, 528, 455 Titanite: 586, 582 Sillimanite: Sinhalite:

Topaz, pink:

455

682

Tourmaline, green: 497 461 415 Tourmaline, red: 555, 537, 525-461, 456, .

Tremolite: 684, 650,

,

451 428

628

Turquoise: (460), 432, (422) Variscite:

688, (650)

Verdite: 700, 699,

455

Vesuvian, brown: 591, 588, 584, 582, 577, Vesuvian, green: (528), 461

574

Vesuvian, yellow-green: 465 Willemite: 583, 540, 490, 442, 431, 421 Zircon, high-zircon: 691, 689, 662, 660, 653, 621, 615, 589, 562, 537, 516, 484, 460,

low

433

zircon: 653, (520)

orange: 640, 630, (540), (536), (533), (530), 520, 517, 515, 5J2. 510, (503), 482, 480, 477, 4Z5, (449), (447), (446)

Zirconia,

39

Absorption Spectra of Selected Gemstones 700

650

600 1

1

550 1

1

1

1

1

1

500

450

400 nm

1

Diamond (Cape

Series)

Diamond (type with

504 tion

nm absorpband)

Ruby

Red spinel

Emerald

Alexandrite

II

i ^11 i!

i

K

ii

-^^H

1

\^m

i

l\W^M

1

!

^B

Almandine garnet

Zircon

Yellow apatite

Yellow-green 1

1

1

1

1

1

1

1

nrrpn,

|.TT.|....

MINIMI

synthetic spinal II

1

1

II II

|

1

700

650

600

550

From Gemmologists' Compendium by R. Webster, NAG Press Edelstemkundliches Handbuch by Professor Dr. Chudoba and Verlag,

Bonn

40

450

500

London Taken from Gubelm, Stollfuss

Ltd., Dr.

400

Transparency

A

factor in the evaluation of most

gemstones

foreign matter and air bubbles or fissures in

The path of light through the

transparency.

absorption lapis

in the crystal.

and

lazuli,

interior of the crystal affect

the-

crystal can also be impaired by strong

Grainy, stalky, or fibrous aggregates (such as chalcedony, are opaque because the rays of light are repeated!)

turcjiioise)

refracted or reflected by the

Where

or absorbed.

their transparency. Inclusions of

is

the-

many

the light

is

tiny laces until finally they are completely reflected

only weakened by

its

passage through

a

stone,

it

is

said

to have translucency.

Luster

The

gem is caused by reflection, i.e., the reflecting of part of the incident back from the surface. It is dependent on the refractive index and the nature of the surface, but not on the color. The higher the refraction, the higher the luster. The most desirable luster is adamantine; the most common is vitreous. Comparatively rareare the greasy, metallic, pearly, silky, and waxy lusters. Stones with no luster arcdescribed as dull. In everyday language, those light effects which are caused by total reflection are also considered as luster. The lower facets of the gem act as a mirror and reflect the entering light more or less completely, thus strengthening the lustrous appearance. The phenomenon on the surface of the stone is called brilliance. The ideal complete luster of a

light

refraction

is

found

in the

diamond

cut,

which thus reaches the highest

reflected ray

entering ray

entering ray

brilliance.

reflected ray

? f

M

refraction

total reflection

Path of a ray of light Principle of reflection

through a

brilliant cut

diamond

Pleochroism Some gems appear to have different colors or depth of color when viewed in different directions. This is caused by the differing absorption of light of doubly refractive crystals. Where two main colors can be observed (only in the tetragonal, hexagonal, and trigonal crystal systems), one speaks of dichroism; where three colors can be seen (only in the orthorhombic, monoclinic, and triclinic crystal systems) of trichroism or pleochroism.

The

latter is a collective description

used for both kinds of the multi-

coloredness.

Amorphous gems and those of the cubic crystal system show no pleochroism. The appearances of the pleochroism can be weak, definite, or strong. It must be taken into consideration when cutting in order to avoid poor colors, or shades that are too dark or too light. The instrument of observation for pleochroism is the dichroscope. (Refer to table of the

pleochroism of selected gemstones on pages 42 and 43.)

41

Pleochroism of Selected

Gemstones

Actinolite:

Alexandrite-

Amblygonite: Amethyst: Anatase: Andalusite: Apatite:

yellow-green, light green, blue-green green alexandrite viewed in daylight: distinct; pigeon-blood red-violet alexandrite in lamplight distinct: dark red, yellow-red, dark green weak red, orange-yellow, emerald-green very weak; purple, gray-purple distinct; yellow,

orange

strong; yellow, olive, red-brown to dark red yellow: weak; golden-yellow, green-yellow

green: weak; yellow, green blue: very strong; blue, colorless

Aquamarine: Aventurine feldspar: Axinite:

Azurite:

blue: distinct; nearly colorless to light blue, blue to sky-blue green/blue: distinct; yellow-green to colorless, blue-green weak or nonexistent strong; olive-green, red-brown, yellow-brown distinct; light blue, dark blue

weak

Barite:

blue:

Benitoite:

very strong; colorless, blue

Brazilianite:

very

weak

Chrysoberyl:

very

Citrine:

natural:

weak; red to yellow, yellow to pale green, green weak; yellow, light yellow

Chrysocolla:

weak

Cordierite:

blue cordierite strong: yellow, dark blue-violet, pale blue; pale blue cordierite strong; almost colorless, dark blue, pale blue synthetic corundum distinct: pale green, yellow-green weak; weak pale yellow, light yellow weak; yellow-green, dark green

Corundum: Danburite: Diopside: Dioptase: Dumortierite: Emerald:

weak; dark emerald-green, light emerald-green strong; black, red-brown, brown natural: distinct; green, blue-green to yellow-green

synthetic: yellow-green, blue-green

Epidote:

distinct; green, yellow-green very weak; whitish-green, yellow-green, blue-green green-brown epidote strong: green, brown, yellow;

Hiddenite:

green epidote strong: almost colorless, light brown distinct: blue-green, emerald-green, yellow-green distinct; blue-green, emerald-green, yellow-green

Enstatite:

Euclase:

Hypersthene:

strong; hyacinth-red, straw-yellow, sky-blue

Kassiterite:

weak

Kornerupine:

strong: green, yellow, reddish-brown

Kunzite:

distinct;

Kyanite:

strong; pale blue to colorless, pale blue, dark blue

Lazulite:

strong; colorless, dark blue

Malachate:

very strong: almost colorless, yeliow-green, dark green

Nephrite:

weak; yellow to brown, green

Orthoclase:

yellow:

Painite:

strong; ruby-red, brown-orange

Peridot:

very weak; colorless to pale green,

Phenacite:

distinct; colorless,

Prasem

very

(Jasper):

Prasiolite:

Precious beryl:

to strong; green-yellow, brown, red-brown

amethyst

weak lively

green, oily green

orange-yellow

weak

weak; liaht green, pale green gold-beryl weak: lemon-yellow, yellow; green beryl: distinct: yellow-green, blue-green; helidor weak: golden-yellow, green-yellow; very

morganite

distinct: pale pink, blue-pink

brown-gray, blood-red distinct: red-yellow, rose-red, red-yellow

Purpurite:

distinct;

Rhododonite: Rose quartz: Ruby:

weak;

Sanidine:

weak

42

color, pale red, colorless

pink, pale pink

strong; yellow-red,

deep carmine red

:

Sapphire:

orange: strong, yellow-brown to orange, nearly colorless yellow: weak; yellow, light yellow green: weak; green-yellow, greenish-yellow blue: distinct; dark blue, greenish-blue purple: distinct; purple, light red synthetic: dark blue, yellow to blue

Scapolite:

pink: colorless, pink

yellow: distinct; colorless, yellow Scheelite:

variable

Sillimanite:

strong; light green, dark green, blue

Smhalite:

distinct;

Smoky

dark: dintmct; brown, red-brown

quartz:

green, light brown, dark

brown

Staurolite:

strong; yellowish, yellowish-red, red

Tanzanite:

very strong; purple, blue, strong; yellow, pink

Thulite: Titanite:

Topaz:

brown

or yellow

green titanite: colorless, green-yellow, reddish-yellow; yellow titanite strong: colorless, green-yellow, reddish red: strong; dark red, yellow, rose-red pink: distinct; colorless, pale pink, pink

yellow: distinct; lemon-yellow, honey-yellow, straw-yellow

brown: distinct; yellow-brown, dull yellow-brown green: distinct; pale green, light blue-green, greenish-white blue:

weak;

light blue, pink, colorless

heat-treated: distinct; pink, colorless Tremolite:

distinct

Turquoise:

weak:

Tourmaline:

red: distinct; dark red, light red

colorless, pale blue or pale

green

pink: distinct; light red, reddish-yellow

yellow: distinct; dark yellow, light yellow

Vesusian:

Vivianite:

brown: distinct; dark brown, light brown green: strong; dark green, yellow-green blue: strong; dark blue, light blue purple: strong; purple, light purple green vesusian weak: yellow-green, yellow-brown; yellow vesusian weak: yellow, almost colorless; brown vesuvian weak: yellow-brown, light-brown strong: blue to indigo, pale yellow, green to blue-green, pale yellowish-green

Willemite:

variable

Zircon

red:

weak;

red, light yellow

red-brown: very weak; reddish-brown, yellowish-brown yellow: very weak; honey-yellow, brown-yellow brown: very weak; red-brown, yellow-brown brown-green: very weak; pink-yellow, lemon-yellow green: very weak; green, brown-green blue: distinct; blue, yellow-gray to colorless

43

Light and Color Effects

Many gems show

striated light effects or color effects

which do not

color and are not caused by impurities or their chemical composition. are caused by reflection, interference, and refraction.

Adularescence a

Moonstone, being a variety of adularia

(see

blue-whitish opalescence which glides over the surface

relate to their

These

name, page

when

164),

the stone

effects

shows is

cut

en cabochon. Interference phenomena of the layered structure are the cause of this effect.

Asterism This is the effect of light rays forming a star (Latin aster, star image); the rays meet in one point and enclose definite angles (depending on the symmetry of the stone). It is created through reflection of light by fibers that lie in various directions. (See photograph on page 45.) Ruby (page 82) and sapphire (page 86) cabochons can Spectrolite, a variety of

the labradorite with especially effective

labradorization; Finnland.

Quartz Cat's Eye. The finest amiant-fibers

cause the chatoyancy

44

Light stars (asterism)

in

blue sapphires and

show effective six-rayed stars. If a

stars.

There

in

ruby.

are also four-rayed stars and, rarely, twelve-rayed

piece of rose quartz has been cut as a sphere, the rays

move in circles over the

whole surface; where included needles are partially destroyed, stunted stars, part circles, or light clusters are formed. Asterism also occurs in synthetic gems.

Aventurization Colorful play of glittering reflections of small, leaf-like inclusions on an opaque background. The inclusions are hematite or goethite in the case of aventurine feldspar (page 166); fuchsite or hematite in aventurine quartz (page 122); and copper scrapings in imitation aventurine glass.

Chatoyancy chat

=

(cat's

eye effect)

=

eye); this

cat, oeil

needles, or channels.

cabochon in such

a

An effect which resembles the slit eye of a cat (French

caused by the reflection of light by parallel fibers, This phenomenon is most effective when the stone is cut en is

is parallel to the fibers. When the gem is rotated, The most precious cat's eye is that of chrysoberyl found in many gemstones; especially well known are

way that the

base

the cat's eye glides over the surface.

(page 98). The effect can be quartz cat's eye, hawk's eye, and tiger's eye (page 124). If one talks simply of cat's eye, one refers to a chrysoberyl cat's eye. All other cat's eye must have an additional designation.

Play of color of some gems caused by dispersion of light in cracks and of the rainbow (Latin iris = rainbow). Commercially, this created by artificially producing cracks in rock crystal.

Iridescence

flaws, resulting in the colors

effect

is

45

i Surface play of color (opalization)

in

black precious opal; Australia.

Labradorescence Play of color in metallic hues, especially in labradorite (hence name) and spectrolite (page 166). Blue and green effects are often found, but the whole spectrum can be observed. The cause of the schillers is most probably interference phenomena of twinned layering. the

Luster

Irridescent luster and tender play of color in pearls.

It is

created through

diffraction and interference of the light at the shingle-like layered aragonite-leafs and in

between skin

layers near the pearl surface (see

page 230).

Opalescence Milky-blue or pearly appearance of common opal (page 152) caused by reflection of short wave, mainly blue, light. It should not be confused with opalization.

Opalization (often called iridescence) Play of color of the opal (hence the name, page 150) which changes with the angle of observation. The electron-microscope shows the cause at a magnification of 20,000 X small spheres of the mineral crys:

tobalite included in a silica gel cause the reflection interference

diameter of these spheres

Silk

is

phenomena. The

one ten-thousandth of a millimeter.

Reflection of parallel fibrous inclusions or canals causes a silk-like appearance. Where the included needles are

Especially desirable in faceted rubies and sapphires.

too numerous, the stone becomes opaque and, a cat's eye.

46

when

cut accordingly, can

show

Luminescence Luminescence (Latin - light) is a collective definition for the emission of visible light under the influence of certain rays, as well as by some physical or chemical reaction, but not including pure heat radiation. The most important of these phenomena for the testing of gems is the luminescence under ultraviolet light, which is called fluorescence. The name fluorescence is derived from the mineral fluorite, which is the substance in which this light phenome non was first observed. When the substance continues to give out light after irradiation has ceased, the effect is called phosphorescence (named after the well-known light property of phosphorus).

The

causes of fluorescence are certain interference factors (impurities or flaws in

Most of the precious- and gemstones respond to shortwave (254 nm). There are gemstones which exclusively react to shortwave, others, only to longwave (366 nm), and again others which react to shortwave as well as longwave UV. Gemstones which contain iron do not show any the structure) in the crystal lattice.

UV

fluorescence.

Fluorescence is in general not suitable for identifying gemstones, because many specimens of a gemstone can fluoresce in completely different colors, while others of the same gemstone may not light up at all under UV. In the detection of synthetic gemstones, on the other hand, fluorescence has proven useful, because syntheses under frequently react differently than natural gemstones. Also glued gemstones can sometimes be identified under when the glue fluoresces by itself or differently than the other parts. Occasionally, fluorescence can help establish a particular source locality, because sometimes typical phenotypes for a certain place are characteristic. Luminescence caused by X rays can help to differentiate between real and cultured pearls. The mother-of-pearl of saltwater pearl oysters does not luminesce, while that of freshwater pearl mussels gives off a strong light. As the inserted nucleus of a cultured pearl has generally been taken from a piece of freshwater mother-of-pearl, the cultured pearl shows a luminescence which the real ones do not have. (Refer to table of the fluorescing gemstones on page 48.)

UV

UV

Fluorescing minerals

in

white

light (left)

and under UV

rays (right). Each

from the

left;

top,

aragonite, calcite; center, fluorite, halite; bottom, willemite.

47

Fluorescence

Gemstones

of Selected

-;.v.f

"f-f

:

"

.•.

-

::-;

?.f-f

.

Moss agate:

r.':~z

Amazonite: weak; dive-green

Amber: 5-

—

bluish to yellow-green :e

black: usually

-6

:

fire:

Ambrygonite: very weak; green Amethyst: weak; greenish Ammolite: mustard-yellow Andalusite: weak; green, yellow-green Apatite, yellow A.: Aventurine. green A.: to pink -.e—.-'-e -e Z5C3-

Pearls:

pale greenish, blue Phosgenite: yellow, orange-yellow

Prehmte: weak, orange Rhodochrosite: weak; red Rose quartz: weak; dark violet Ruby: strong; carmine red

z=-» sz-z-:.'.-

Be- :: :e Caldte: red. pink, orange, white, yellow- :e

:'.

.£

Z'~"

~k

Z

Sapphire: blue: violet or none yellow: weak; orange

Z - 5-

:

C-3 :e::". z - s~-.\ e Chrysoberyl: green: weak; dark red. r

:-.-£'5

colorless:

-

-:-f

yellow: violet, blue-red Scheelite: strong, light blue

Smithsonite: blue-white, pink,

.

Smoky

Sodalite: strong,

.•.£ =

:

«

z -£-.•.- :e

-e

-:*"£ -5-3 E-: 3se .f3v :- -;-e : ..:- :e -5-3 sv:-; : .e :: -3-:f-;:e -5-3 -:~e :-:e

Spinel: red: strong; red

,:e:

-veak;

.

orange -f :z"

:e

.-.£ =

: e:

.

- 3 .•.-

Komerupine: usually none; green K. from Kenia: yellow Kunzite: strong; yellow-red, orange -3:-3z:-:e


-8

Refractive index:

1.564-1.596 Double refraction: -0.004 to -0.005 Dispersion: 0.014(0.009-0.013)

1

Density:

Group

2.68-2.74

Cleavage: Indistinct Fracture: Conchoidal, uneven, brittle Crystal system: (Hexagonal), hexagonal prisms Chemical composition: AI 2 Be 3 (Si 6 18) aluminum beryllium silicate

Pleochroism: Definite; nearly colorless, light blue, blue, light green

Absorption: 537, 456, 427 Maxixe-A: 695, 655, 628, 615, 581, 550 Fluorescence: None

Aquamarine (Latin — water of the sea) is so named because of its sea water color. A dark blue is the most desired color. The coloring agent is iron. Lower qualities are heated to 725-850 degrees F (400-450 degrees C) to change them to the desired, permanent aquamarine blue. Higher heat will lead to discoloration. Care must be taken when making jewelry! Colors can also be improved with neutron and gamma irradiation, but these changes do not last. Aquamarine is brittle and sensitive to pressure. Inclusions of fine, oriented hollow rods or aligned foreign minerals cause a cat's

eye effect or asterism with six-rayed stars with a vivid sheen.

Santa Maria Quality name for especially with the same name in Ceara (Brazil). Santa-Maria-Af ricana the market since 1991.

r^i

fine

aquamarine.

Named

after the

mine

Quality name for fine aquamarine from Mozambique, on derived from the "Santa Maria" quality of Ceara

Name

(Brazil).

Maxixe-Aquamarine Deep it came only from

blue aquamarine; color fades in daylight. Originally

(since 1917)

1970s

it

the Maxixe

Mine

in

Minas Gerais (Brazil). Since the made more beautiful through

has been widely available, but obviously

irradiation, but the color does not last.

Deposits The most important deposits are in Brazil, spread throughout the counThe well-known deposits in Russia and the Urals seem to be worked out. Other deposits of local importance are in Australia (Queenland), Burma (Myanmar), China, India, Kenya, Madagascar, Mozambique, Namibia, Nigeria, Zambia, Zimbabwe, Sri Lanka, Tanzania, and the United States. The host rock is pegmatite and coarsegrained granite as well as their weathered material. The largest aquamarine of gemstone quality was found in 1910 in Marambaya, Minas Gerais (Brazil). It weighed 243 lb (110.5 kg), was 18 in (48.5 cm) long and 15!/? in (42 cm) in diameter, and was cut into many stones with a total weight of over 100,000 ct. There have been finds weighing a few tons, but these aquamarines are opaque and try.

gray,

not suitable for cutting.

The

preferred cuts are step (emerald) and scissors-cut with rectangular or long

oval shapes. Turbid stones are cut en

Confusion

cabochon or are used

for necklace beads.

With

euclase (page 178), kyanite (page 196), topaz (page 102), tourmaline (page 110), zircon (page 108), and glass imitations. Synthetic aquamarine can be produced but is uneconomical. The "synthetic aquamarine" sold Possibilities for

in the trade

is

Aquamarine, Aquamarine, 3 Aquamarine, 4 Aquamarine, 1

2

94

really

aquamarine-colored synthetic

octagon, 72.46ct octagon, 1 7.41 ct antique cut, 45.38ct navette, 25.58ct

spinel.

5 Aquamarine, antique cut, 18.98ct 6 Aquamarine, briolette, 6.65ct 7 Aquamarine, cyrstal, 68.5mm, 45g 8 Aquamarine, 3 crystals, together 77g

^»H

*>&'"'

Beryl

Precious Beryl Color: Gold-yellow, yellow-green, yellow,

Refractive index:

Double

pink, colorless

Color of streak: White Mohs' hardness: 7V2-8 Density: 2.66-2.87 Cleavage: Indistinct Fracture: Conchotdal, brittle Crystal system: (Hexagonal), hexagonal

pnsms Chemical composition: AI 2 Be 3 {Si 6

aluminum berylium

18)

silicate

Group

1.562-1.602

refraction:

-0.004

to

-0.010

Dispersion: 0.014(0.009-0.013)

Pleochroism: Golden: weak; lemon-yellow, yellow Heliodor: weak; golden-yellow, greenyellow Morganite: definite; pale pink, bluish-pink Green: definite; yellow-green, blue-green Absorption spectrum: Not usable Fluorescence: Morganite: weak; violet

Transparency: Transparent to opaque

Precious beryl refers to all color varieties of the beryl group that are not emeraldgreen (page 90) and not aquamarine-blue (page 94). Precious beryls are brittle and therefore sensitive to pressure and resistant to chemicals used in the household, and they have a vitreous luster, occasionally displaying the cat's eye effect and asterism. They are typically found with aquamarine (page 94). Often used with a step cut. Color varieties have either special names in the trade, or the respective color precedes the word beryl (e.g., yellow beryl). Bixbit

Gooseberry- red. Origin of the name is unknown. Occurrences in Utah (United States).

[3]

Many scientists

reject

this as separate variety.

Golden Beryl

[

1

]

Color varies between lemon-yellow and golden-yellow. Inclusions

are rare. Decolorization at 482 degrees

F

(250 degrees C). Deposits in Madagascar,

Namibia, Nigeria, Zimbabwe, Sri Lanka. Colorless beryl, named after locality in Goshen, Massachusetts [5] (United States). Used as imitation for diamond and emerald by applying silver or green metal foil to the cut stone. Occurrences in Brazil, China, Canada, Mexico, Russia, and the United States.

Goshenite

Light yellow-green (Greek — present of the sun). Discovered in 1910 variety in Namibia, but beryls of the same color were previously known in Brazil and Madagascar. Since there is no clear distinction possible in the yellow and green-yellow tones in comparison to golden beryl, heliodors are generally rejected as an independent precious beryl variety and rather are counted among the weak-colored golden beryls.

Heliodor

as

[2,6]

apparent

Morganite

new

[4]

(Also called pink beryl) Soft pink to violet, also salmon-colored.

Named after the American banker and collector J. P. Morgan. Density between 2.71 and 2.90. Inferior qualities can be improved by heating above 752 degrees F (400 degrees C). Deposits in Afghanistan, Brazil, China, Madagascar, Mozambique, Namibia, Zimbabwe, and the United States (Utah, California). Synthetic morganite is known. Inclusions are rare.

Possibilities for

Confusion

With many gemstones because of

the richness of

colors of the precious beryls. Greenish precious beryls are transferred into blue

aquamarine stones through heating at 725-930 degrees F (444-500 degrees C). No consensus exists concerning the demarcation between the green precious beryl and emerald (page 90), since a distinction with the naked eye is not possible. Chrome-tinted green beryls count, according to "CIBJO," unconditionally among the emeralds. 1

Golden

beryl,

antique cut, 28.36ct

45.24ct 3 Bixbite, antique cut, 49.73ct 4 Morganite, antique cut, 23.94ct 2 Heliodor, antique cut,

96

Goshenite, navette, 25.58ct oval, 29.79ct 7 Beryl, two crystals, together 32. 5g 8 Morganite, rough, 24. 5g 5.

6 Heliodor,

,.

^

t

-

^

Chrysoberyl

^^

Color: Golden-yellow, green-yellow, green,

aluminum oxide Transparency: Transparent to opaque Refractive Index: 1.746-1.763

brownish, red Color of streak: White Mohs' hardness: 8V2 Density:

Cleavage: Fracture:

Double

3.70-3.78

Good Weak conchoidal, uneven

Crystal system

:

+0.007 to +0.011

Pleochroism: Very weak: red to yellow, yellow to light green, green Absorption: 504, 495, 485, 445 Fluorescence: Usually none Green: weak; dark red

(Orthorhombic), thick-

tabled, intergrown triplets

Chemical composition: BeAi 2

SdX

refraction:

Dispersion: 0.015(0.011)

4 beryllium

Chrysoberyl (Greek — gold) has been known since antiquity; the varieties alexandrite and chrysoberyl cat's eye are especially valued. The host rock is granite pegmatite, mica schist, and placers. Deposits of the actual chrysoberyl (numbers 3, 9, and 10 below) are in Brazil (Minas Gerais, Espirito Santo) and Sri Lanka, as well as Burma (Myanmar), Madagascar, Russia (Urals), Zimbabwe, and the United States. Stones are fashioned mainly in step, Ceylon, and brilliant cuts. The famous Hope chrysoberyl (London), a light green, faceted stone of 45ct is completely clean. Possibilities for Confusion With andalusite (page 178), brasiliante (page 190), golden beryl (page 96), hiddenite (page 114), periodot (page 158), sapphire (page 86), sinhalite (page 186), skapolite (page 188), spinel (page 100), topaz (page 102), tour-

maline (page

110),

and zircon (page

108).

Czar Alexander II) Was discovered only as regreen in daylight, and light red in artificial incandescent light. This changing of color is best seen in thick stones. Alexandrite displaying the cat's eye effect is a great rarity. Care must be taken when working with it, as it is sensitive to knocks and color changes are possible with exposure to great heat.

Alexandrite [5—8]

(Named

cently as 1830 in the Urals. It

after

is

The deposits in the Urals are worked out. Today it is mined in Sri Lanka and Zimbabwe, and since the end of the 1980s especially in Brazil (Minas Gerais). Deposits are also found in Burma, India, Madagascar, Tanzania, Tasmania, and the United States. The largest stone, 1876ct, was found in Sri Lanka. The largest cut alexandrite weighs 66ct;

it is

in the

Possibilities for

Smithsonian Institution

Confusion

in

Washington, D.C. (United

With synthetic corundum, synthetic spinel

States).

(page 243),

andalusite (page 178), pyrope (page 104). Doublets with good color change are available with red garnet on top, red glass underneath. Synthetic alexandrite is also

known.

Chrysoberyl Cat's Eye [2, 4] (Also called cymophane; Greek — waving light) Fine, parallel inclusions produce a silver- white line, which appears as a moving light ray in a cut stone. The name chrysoberyl cat's eye is derived from this effect, which reminds one of the pupil of a cat. The short term "cat's eye" always refers to chrysoberyl; all other cat's eye must be designated by an additional name. There are deposits in Sri Lanka and Brazil, as well as in China, India, and Zimbabwe. Possibilities for

Confusion

With quartz

(page 188). Synthetic chrysoberyl

1

Chrysoberyl

in

mother-rock

2 Chrysoberyl cat's eye, 24.09ct

3 Chrysoberyl, 3.36 and 2.23ct cat's eye, 4.33ct 5 Alexandrite in daylight and

4 Chrysoberyl

artificial light

6 Alexandrite,

98

oval,

0.80ct

cat's

cat's eye (page 124), prehnite eye and doublets are known.

cat's

7 Alexandrite, intergrown

eye

triplet

crystal

8 Alexandrite cat's eye, 2.48ct 9 Chrysoberyl, oval, 9.24ct 10 Chrysoberyl, antique cut, 2.1 1 Chrysoberyl crystal 12 Chrysoberyl in mother-rock

1

ct

©

Spinel magnesium aluminium oxiae Transparency: transparent to opaque

Color: Red, yellow, brown, blue, green,

black

Color of streak: White Moh's hardness: 8 Density: 3.54-3.63 Cleavage: Indistinct Fracture: Conchoidal, uneven

Refractive index: 1.712-1.762

Double refraction None Dispersion: 0.020(0.011) Pleochroism: Absent :

Crystal system: (Cubic), octahedron, twins,

rhombic dodecahedron Chemical composition: MgAI 2

4

Absorption: red Sp.: 685, 684, 675, 665, 656, 650, 642, 632, 595-490, 465, 455 Fluorescence: Red Sp. strong: red; Blue Sp. weak: reddish, green

In mineralology spinel classifies a whole group of related minerals; only a few are of gemstone quality. The origin of name is uncertain, perhaps Greek "spark" or Latin "point." Spinel occurs in all colors, the favorite being a ruby-like red. The coloring

agents are iron, chrome, vanadium, and cobalt. Large stones are rare and star spinels are very rare.

Rubicell

Old name

[9]

Balas spinel

for yellowish, orange, and

brownish

variety.

Falsely called Balas ruby (after a region of Afghanistan). Pale red

[4]

variety.

Pleonaste

Also called Ceylonite. Dark green to blackish, opaque spinel which A2 4 density 3.63-3.90).

[1]

contains iron (Mg,Fe)

Gahnite

ZnA 2

;

Dark green

Hercynite

Also

known

to black spinel, containing iron.

as

Zinc

spinel. Blue, violet, or

4 ; density 4.00-4.62. (See

Gahnospinel

page 204, no.

FeA 2

4

;

density 3.95.

dark green to blackish spinel.

1).

Blue to dark blue spinel, containing iron. (MgZn)Al 7

4

;

density

3.58-4.06. Picotite

Also called

Chrome

spinel.

Brownish, dark green, or blackish

spinel.

Fe

(Al,Cr 2 )0 4 density 4.42. ;

Spinel was recognized as an individual mineral only 150 years ago. Before then

it

was

Some well-known "rubies" are really spinels, such as the "Black Prince's Ruby" in the English Crown (see photo, page 9) and the 361ct "Timur Ruby" in a necklace in the English Crown Jewels. The drop-shaped spinels in the Witclassed as ruby.

crown of 1830 were also originally thought to be rubies. Occurs with ruby and sapphire in placer deposits, mainly in Burma (near Mogok) and Sri Lanka (near Ratnapura). Other deposits are found in Afghanistan, Australia, Brazil, Madagascar, Nepal, Nigeria, Tadzhikistan, Tanzania, Thailand, and the United States (New Jersey). The two largest spinels (formed as roundish octahedrons) weigh 5 2 Oct each and are in the British Museum of London. The diamond fund in Moscow owns a spinel that weighs over 400ct. telsbacher's

Confusion

With amethyst (page

118), chrysoberyl (page 98), topaz (page 102), tourmaline (page 110), and zircon (page 108). Synthetic spinels have been on the market since the 1920s (compare to page 243). They imitate not only natural spinel, but also many other gemstones,

Possibilities for

pyrope (page

104), sapphire (page 86),

especially ruby. 1

Pleonaste crystals

2 Spinel, 28.47

and

in

mother-rock

4.1 6ct

3 Spinel, 3 faceted stones

4

Spinel, so-called balas

ruby 17.1 3ct

5 Spinel, antique cut, 5.05ct

6 Spinel, two

100

ovals,

7.96 and 5.32ct

7 Spinel, blue, 15.08 and 30.1 1 ct 8 Spinel, 12 different reds 9 Spinel, rubicelle, 3.14 and 5.07ct 10 Spinel, crystals and other rough

stones

Topaz

Precious Topaz

Color: Colorless, yellow, red-brown, light blue, pink-red, red, violet, light

green

^ft\

xLLJJ

^C'

Transparency: Transparent, translucent Refractive index:

Color of streak: White Moh's hardness: 8 Density: 3.49-3.57 Cleavage: Perfect Fracture: Conchoidal, uneven Crystal system: Orthorhombic, prisms with multi-faceted ends, often 8-sided in cross-section striations along length Chemical composition: AI 2 [(F,0H) 2 /Si0 4 ] fluor containing aluminium silicate

Double

1.609-1.643

refraction:

+0.008

to

+0.016

Dispersion: 0.014(0.008)

Pleochroism: Yellow: definite; lemon-honey, straw-yellow Blue:

weak;

light blue, pink, colorless

Red: strong; dark red, yellow, pink-red Absorption spectrum: Pink: 682 Fluorescence: Pink: weak; brown Red: weak; yellow-brown Yellow: weak; orange-yellow

Formerly, the name topaz was not applied consistently or specifically; one called all yellow and golden-brown, and sometimes also green, gemstones topaz. The name topaz is most probably derived from a place of discovery on an island in the Red Sea, now Zebirget but formerly Topazos. Colors of the gemstone that is today called topaz are rarely vivid. The most

common color is yellow with a red tint; the most valuable is pink to reddish-orange. The coloring agents are iron and chrome. Some yellowish-brown varieties of certain deposits gradually fade in the sunlight.

Care must be taken during polishing and setting because of the danger of cleavage. are also not resistant to hot sulphuric acid. The luster is vitreous. Deposits are associated with pegmatites or secondary placers. During the 18th century, the most famous topaz mine was at Schneckenstein in the southern Vogtland in Saxony. Today, Brazil (Minas Gerais) is the most important supplier. Other deposits are in Afghanistan, Australia, Burma (Myanmar), China, Japan, Madagascar, Mexico, Namibia, Nigeria, Pakistan, Russia (the Urals, Transbaikalia), Zimbabwe, Sri Lanka, and the United States (Utah). Light blue topazes are found also in Northern Ireland, Scotland, and Cornwall, England. Topazes weighing several pounds are known. In 1964 some blue topazes were found in the Ukraine, each weighing about 220 lb. (100 kg). The Smithsonian Institution in Washington, D.C., in the United States owns cut topazes of several thousand carats each. Colored stones are usually step- (emerald) or scissor-cut, and colorless ones or weakly colored ones are brilliant-cut. Topazes with disordered inclusions are cut en cabochon.

They

XS^ I

Possibilities for

Confusion

With

apatite (page 194),

aquamarine (page

164), bra-

(page 190), chrysoberyl (page 98), citrine (page 120), danburite (page 182), diamond (page 70), precious beryl (page 96), fluorite (page 198), kunzite (page 114), orthoclase (page 164), phenakite (page 180), ruby (page 82), sapphire (page 86), spinel zilianite

(page 100), tourmaline (page 110), and zircon (page 108). Since 1976, blue synthetic topazes are known. Some yellowish topazes of certain deposits turn pink, blue, or colorless through heating. Since the quartz variety citrine (page 120) and yellow heat-treated amethyst (page 118) are in the trade often falsely called "gold topaz" or "Madeira topaz," real topaz is sometimes called precious topaz, in

1

order to clearly distinguish them. 6 Topaz, fancy

Topaz, rectangle, 46.6 1ct, Brazil

2 Topaz, rough, 225.50ct, Brazil

3 Topaz, crystal cleavage, 18.00ct, oval, 93.05ct,

Afghanistan

5 Topaz, octagon, 88.30ct, Brazil

102

32 44ct

Russia

Brazil

4 Topaz,

cut,

7 Topaz, 2 faceted ovals, 53.75ct,

1

8 Topaz, cabochon, 17.37ct, Brazil 9 Topaz, crystal, 65.00ct, Brazil Topaz, crystal in mother-rock

Garnet Group This

a

is

group of

differently colored minerals with similar crystal structure and

related chemical composition.

The main

representatives are pyrope, almandine and

spessartine (pyralspite-row), grossular, andradite, and uvarovite (ugrandite-row).

Within the rows are also mixed members. The name derives from the Latin for grain because of the rounded crystals and similarity to the red blossoms of the pomegranate tree.

Garnet, in the popular sense,

is

usually understood only as the red "carbuncle

stones" pyrope and almandine.

Data

common

to

all

Fracture: Conchoidal, splintery, brittle Transparency: Transparent to opaque

garnets:

Color or streak: White Mohs' hardness: 6V2-IV2 Cleavage: Indistinct Crystal system: (Cubic) rhombic dodecahedron, icositetrahedron

Pyrope

Double

none

[4, 51

red- brown Density: 4.12-4.18

Orange to

Color:

refraction: Normally

Pleochroism: Absent Fluroescence: Mostly none Luster: Vitreous

Chemical composition:

Mn 3 AI 2 (Si0 4

manganese aluminum

Pyrope (Greek —

Transparency: Transparent, translucent Refractive index: )3

1.790-1.820

Dispersion: 0.027(0.015)

Absorption: 495, 485, 462, 432, 424, 412

silicate

was the fashion stone of the 18th and 19th centuries, the are found in Burma (Myanmar), China, Madagascar, Sri Lanka, South Africa, Tanzania, and the United States. Can be confused with almandine (see below), ruby (page 82), spinel (page 100), and tourmaline (page 110). fiery)

"Bohemian Garnet." Deposits

Imitations are

Rhodolite

made with

[6, 7, 8]

Almandine

red glass.

Rose-red pyrope variety.

Garnet Group

[9,10]

Color: Red with violet tint

Density:

1.770-1.820 Dispersion: 0.027 (0.013-0.016)

Refractive index:

3.93-4.30

Chemical composition: Fe 3 AI 2 (Si04)3 aluminium silicate

iron

Absorption: 617, 576, 526, 505, 476, 462, 438, 428. 404,193

Its name is derived from the town in Asia Minor. Deposits are found in Brazil, India, Madagascar, Sri Lanka, as well as the Czech Republic and Austria. Can be confused with pyrope (see above), ruby (page 82), spinel (page 100), and tourmaline (page 110).

Spessartine Color:

Garnet Group

[2, 3]

Orange to red-brown

Density: 4.12-4.18 Chemical composition: Mn3AI 2 (Si0 4 ) 3 manqanese aluminium silicate

Transparency: Transparent, translucent Refractive index:

1.790-1.820

Dispersion: 0.027(0.015)

Absorption: 495, 485, 462, 432, 424, 412

name is derived from occurrence in the Spessart ( = forest), Germany. Deposits are found in Burma (Myanmar), Brazil, China, Kenya, Madagascar, Sri Lanka, Tanzania, and the United States. The best specimens come from Namibia ("Mandarin Spessaratine"). Can be confused with andalusite (page 178), chrysoberyl (page 98), fire opal (page 152), hessonite (page 106), titanite (page 194), and topaz (page 102). Its

1

Range of garnet

3 Spessartite, 3

4 Pyrope

green-yellow-brown-red mother-rock

colors,

2 Spessartite crystal

in

cabochons

crystal, icosate'trahedron

5 Pyrope, three-faceted stones

104

6 7 8 9 10

Rhodolite, brilliant cut, 4.02ct Rhodolite, navette, 2 ovals

Rhodolite crystal, rolled

Almadine

in mica Almandine, trapezoid,

oval,

octagon

•&«

#

#

Tourmaline Group The

tourmaline group refers to

a

number of crystal

Color: Colorless, pink, red, yellow, brown, green, blue, violet, black, multicolored

Double refraction: -0.014 to -0.032 Disperson: 0.017 (0.009-0.011) Pleochroism: Red t.: definite: dark red,

Color of streak: White Mohs' hardness: 7-7 Vi Density: 2.82-3.32 Cleavage: Indistinct

^

light

red;

Brown t: definite: dark brown, light brown; Green t: strong: dark green, yellow-

Fracture: Uneven, smalt conchoidal, brittle

Crystal system: (Trigonal), long crystals with triangular cross section

and rounded to main

green; Blue t. strong: dark blue, light blue Absorption spectrum: Cannot be evaluated Fluorescence: Weak or none

sides, definite striation parallel

^

varieties.

Refractive index: 1.614-1 .660

:

axis

Transparency: Transparent, opaque

Even though tourmaline has been known since antiquity in the Mediterranean region, the Dutch imported it only in 1703 from Sri Lanka to Western and Central Europe. to

They gave

mean

the

new gemstones

According to

Sinhalese name, Turamali, which

is

thought

recognized in the trade:

color, the following varieties are

Achroite

(Greek— without

Rubellite

[page 112, nos. 2, 4] (Latin is the most valuable.

tint;

a

"stone with mixed colors."

color) colorless or almost colorless, quite rare.

— reddish) pink to red, sometimes with a violet

ruby color

Dravite [page 112, nos. 1, brown. Verdelite [page 112, nos. Indigolite

[page 112, nos.

7, 8]

("Drave" in Karnten/ Austria) yellow-brown to dark

6, 13]

("green stone") green in

3, 5, 11, 15]

named

(after finds in Urals) lilac to violet blue;

Siberite

all

shades.

(after color) blue in all shades.

sometimes used

as a

synonym

for

rubellite.

Schorl [4, 5] black, very an old mining term.

common; used

for

mourning

jewelry.

Name

derived from

Recently, instead of variety names, more and more frequently color names are simply added to the word tourmaline, e.g., yellow tourmaline, pink tourmaline. Mineralogy distinguishes tourmalines according to their chemical composition. The individual members have the following names: (after the island Elba/Italy) Na(Li,Al) 3 Al 6 [(OH) 4 l(B0 3 )3lSi 6

Elbaite

=

18 ]

lithium tourmaline

Dravite (after a deposit near the river Drave, Karnten/Austria) [(OH) 4 l(B0 3 ) 3 Si 6 18 ] = magnesium tourmaline

NaMg

3

Al 6

Schorl (after an old mining expression for "false ore") NaFe 3 (Al,Fe) 6 [(OH) 4 l(B0 3 ) 3 lSi 6 18 = iron tourmaline iron tourmaline Buergerite (after U.S. scholar) NaFe 3 Al 6 [Fl0 3 (B0 3 ) 3 lSi 6 lf ]

l

Tsilaisite

(after a local

name

in

Madagascar)

NaMn

3

Al 6 [(OH) 4

I

(B0 3 ) 3 lSi 6

18 ]

=

manganese tourmaline Uvite

(after a

province in Sri Lanka)

CaMg

3

(Al 5 ,Mg)[(OH) 4 l(B0 3 ) 3 lSi 6

18 ]

=

magnesium tourmaline Liddiocoatite

(after U.S.

gemologist) Ca(Li,Al) 3 Al 6 [(OH) 4 l(B0 3 ) 3 lSi 6

18 ]

=

cal-

cium tourmaline tourmaline, 8 polished cross sections 2 Rubellite cat's eye, 1 .87ct 3 Tourmaline, crystals stem-like on quartz 1

110

4

Schorl, crystals,

5 Schorl

in

opaque

quartz, partly polished

6 Tourmaline "watermelon" 7 Verdelite, 2 crystals

8 Multicolored tourmaline,

crystal

Uni-colored tourmalines are quite

Most There

rare.

crystal or also different colors [6, 8].

crystals are various tones at the

same

are colorless tourmalines with black

green ones with red crystal ends, and some with different-colored layers. whose core is red, the inner layer white, and the outer layer green — called "watermelon" [6].

crystal ends,

There

are stones

Tourmaline

cat's

eyes exits in various colors, but only in the green and pink

varieties [page 110, no. 2]

the chatoyancy strong, caused by fiber-like inclusions of

is

foreign crystals or by thin cavities. artificial light.

They have

Some

a vitreous

tourmalines show a slight change of color in sheen on crystal surfaces, a greasy sheen on

fractured surfaces.

By heating and subsequent rubbing, a tourmaline crystal will

cooling, as well as

by applying pressure,

become electrically charged.

i.e.,

by

then attract dust particles as well as small pieces of paper (pyro- and piezo-electricity). The Dutch, who first imported tourmaline into Europe, knew of this effect. They used a heated stone to pull ash out of their meerschaum pipes and thus called this strange stone aschentrekker (ash puller). For a long time this was the proper name for a tourmaline. Due to this pyroelectrical effect, tourmaline has to be cleaned more often than other gemstones. Deposits are found in pegmatites and alluvial deposits. The most important tourmaline supplier is Brazil (Minas Gerais, Paraiba). Other deposits are in AfIt will

ghanistan, Australia, Burma (Myanmar), India, Madagascar, Malawi, Mozambique, Namibia, Nepal, Nigeria, Pakistan, Russia, Zambia, Zimbabwe, Sri Lanka, Tanzania, the United States (California, Maine), and Zaire. In Europe, there are tourmaline deposits on Elba (Italy) and in Switzerland (Tessin). The most desired colors are pink, intensive pink, and green. It is used in different cuts. Because of the strong pleochroism, dark stones must be cut so that the table lies parallel to the main axis. In the case of pale stones, the table should be perpendicular to the long axis in order to obtain the deeper color. By heating to 842-1202 degrees F (450-650 degrees C), color changes can be produced in some tourmalines. Green tourmaline becomes emerald-green, reddishbrown or fiery red; others are lightened. The color of tourmalines which have been changed with gamma-irradiation is not permanent. Synthetic tourmalines are used

only for research purposes. The stones, offered as synthetic tourmaline, are really tourmaline-colored synthetic spinels.

Possibilities for

Confusion

With many gemstones, due

to the large variety of

(page 178), chrysoberyl (page 98), citrine (page 120), demantoid (page 106), hiddenite (page 114), kunzite (page 114), morganite (page 96), peridot (page 158), prasiolite (page 120), ruby (page 82), emerald colors, especially

amethyst (page

118), andalusite

(page 90), topaz (page 102), vesuvianite (page 186), zircon (page 108), and glass imitations.

1

10

Dravite, 2 faceted stones

Indicolite, crystal

2 Rubellite, oval, 1.73ct

11 Indicolite, faceted, 2.97ct

3 Indicolite, octagon, 6.98ct

12 Indicolite crystal 13 Verdelite, 2 cabochons, 9.77ct 14 Tourmaline, 2 faceted yellowgreen stones 15 Indicolite, 3 cabochons 16 Tourmaline, multi-colored, 24ct

4

Rubellite, 2 faceted stones, together

4.55ct

and antique cut 6 Verdelite, oval, 19.88ct 7 Dravite, cabochon, 19.97ct 8 Dravite, 3 faceted stones 9 Rubellite, oval, 6.16ct 5 Indicolite, octagon

The

112

illustrations are

20 percent

larger than the originals.

17 Rubellite, 3 cabochons 18 Tourmaline, 3 crystals

Spodumene Group refers to the mineral spodumene (Greek — ash-colored); it is mostly opaque, white to yellowish. For a long time gem varieties have been known as hiddenite and kunzite; since the 1970s some isolated transparent colorless varieties have been found. Most recently yellow and green varieties have also been known. Rarely displays the cat's eye effect.

The name

Hiddenite [1-3,

Spodumene Group

8]

Color: Yellow-green, green •yellow, emerald-

green

aluminium

silicate

Transparency: Transparent

Color of streak: White Mohs' hardness: 616-7 Density: 3.15-3.21 Cleavage: Perfect

Refractive index: 1.660-1.681

Double

Fracture: Uneven, brittle

Crystal system: Monoclinic

prismatic,

tabular

Chemical composition:

refraction:

+0.014

to

+0.016

Dispersion: 0.017(0.010)

LiAI(Si 2

6 ) lithium

Pleochroism: Definite; blue-green, emeraldgreen, yellow-green Absorption spectrum: 690, 686, 669, 646, 620, 437, 433 Fluorescence: Very weak; red-yellow

Named

after W. E. Hidden who discovered this stone in 1879 in North Carolina (United States). The coloring agent is chrome or iron. Colors can gradually fade; has a strong vitreous luster. Usually used with the step cut (emerald). In order to display strong colors (due to pleochroism), the table facet must be perpendicular to the main axis of the stone. Deposits occur in granite pegmatite. Deposits found in Burma (Myanmar), Brazil (Minas Gerais), Madagascar, and the United States (North Carolina, California). Can be confused with chrysoberyl (page 98), diopside (page 190), precious beryl (page 96), peridot (page 158), emerald (page 90), and verdelite (page 110).

Spodumene Group

Kunzite [4-7] aluminium

Color: Pink-violet, light violet

Color of streak White Mohs' hardness: 6K2-7 Density: 3.15-3.21

silicate

Transparency: Transparent

:

Refractive index: 1.660-1.681

Double refraction: +0.014 to +0.016 Dispersion: 0.017(0.010) Pleochroism: Definite; amethyst color, pale

Cleavage: Perfect Fracture: Uneven, brittle Crystal system: Monoclinic; prismatic,

red, colorless

Absorption spectrum: Cannot be evaluated

tabular

Chemical composition:

LiAI(Si

?

6) lithium

Fluorescence: Strong; yellow-red, orange

Named after the U.S. mineralogist G. F. Kunz, who first described this gem in 1902. The coloring agent is manganese. Stones are mostly light colored; colors can fade. Brownish and green-violet types can be improved degrees

F.

fractures.

to the

(150 degrees C).

There

in color

by heating

to about

300

are frequently aligned inclusions such as tubes or

The stone has a vivid vitreous luster. The Table facet must be perpendicular axis of the stone. Deposits occur in granite pegmatite. The main producer

main

is Brazil (Minas Gerais). Other deposits are found in Afghanistan, Burma (Myanmar), Madagascar, Pakistan, and the United States. Can be consused with many pinkcolored stones, especially amethyst (page 118), morganite (page 96), petalite (page 188), rose quartz (page 122), rubellite (page 110), sapphire (page 86), and topaz (page 102), as well as colored glass.

1

Hiddenite, octagon, 22.03ct

2 Hiddenite, pear-shaped, 9.30ct 3 Hiddenite, octagon, 19.1 4ct

4 Kunzite, octagon, 16.32ct

114

5 Kunzite, oval, 3.13ct 6 Kunzite, antique cut, 6.1 1 ct 7 Kunzite, 2 crystals 8 Hiddenite, crystal and broken piece

Quartz Group //l\

Quartz (named after a Slavic word for "hard") is the name for a group of minerals of same chemical composition (Si0 2 ) and similar physical properties.

the

Macrocrystalline quartz (crystals recognizable with the naked eye) includes ameamethyst quartz, aventurine, rock crystal, blue quartz, citrine, hawk's eye, prase, prasiolite, quartz cat's eye, smoky quartz, rose quartz, and tiger's eye. thyst,

Microcrystalline quartz (microscopically small crystals) includes agate, fossilized wood, chalcedony, chrysoprase, heliotrope, jasper, cornelian, moss agate, and sard.

Rock Crystal [8-11]

Quartz Group

Color: Colorless

Transparency: Transparent

Color of streak White Mohs' hardness: 7 Density: 2.65 Cleavage: None Fracture: Concboidal, very brittle Crystal system: (Trigonal), hexagonal prisms Chemical composition: Si0 2 silicon dioxide

Refractive index:

:

Dou bte

1.544-1.553

refraction

+

:

.009

Dispersion: 0.013(0.008)

Pleochrosim: Absent Absorption spectrum: Cannot be evaluated Fluorescence:

None

The name

crystal comes from the Greek for "ice," as it was believed that rock crystal was eternally frozen. Rock crystals weighing many tons have been found. Cuttable material is rare. Inclusions are of goethite [star quartz, no. 12], gold, pyrite, rutile, and tourmaline [page 111, no. 5]; the luster is vitreous. Important deposits, among others all over the world, are found in Brazil, Madagascar, the United States, and the Alps. They are used for costume jewelry and delicate bowls and to imitate diamonds. Rock crystal alters to a

colorless

gems

smoky

color with

gamma

as well as glass. Synthetic

irradiation.

rock crystal

Can be confused

with many used only for industrial

is

purposes.

Smoky Quartz Color:

Brown to

Quartz Group

[1-7]

black,

smoky gray

Color of streak: White Mohs' hardness: 7 Density: 2.65 Cleavage: None Fracture: Conchoidal, very

Transparency: Transparent Refractive index:

Double

1.544-1.553

refraction:

+0.009

Dispersion: 0.013(0.008)

Pleochroism: Dark: definite; brown, brittle

Crystal system: (Trigonal), hexagonal prisms

Chemical composition: Si0 2

silicon dioxide

reddish-brown Absorption spectrum: Cannot be evaluated Fluorescence: Usually

none

Named

after its smoky color. Very dark stones are called "morion."Cause of color is probably impurities such as aluminum. The name smoky topaz is improper and no longer acceptable in the trade. Frequenc inclusions are rutile needles [nos. 1, 2]. Deposits in Brazil, Madagascar, Russia, Scotland, Switzerland, and Ukraine. It is used just as rock crystal. Synthetic smoky quartz is not known. Can be confused with andalusite (page 178), axinite (page 182), sanidine (page 204), tourmaline (page 110), and vesuvianite (idocvase, page 186).

Smoky quartz with rutile inclusions Smoky quartz with rutile, cabochon 3 Smoky quartz, oval, 3.8g 4 Smoky quartz, two crystals 5 Smoky quartz, octagon, 5.6g 6 Smoky quartz, oval, 6.2g 7 Smoky quartz crystal

8 Rock

1

116

4 stones, faceted and

crystal,

cabochon 9 Rock crystal,

2

10 Rock 1 Rock 1

crystals

and twins 5g

crystal, brilliant cut,

baguette,

crystal,

Star quartz,

1

5g

1

.8g

• .

r

If

;

*

Amethyst

. Density 5.9-6.1. Monoclinic,

Pb[Cr0 4 ]. Adamantine

luster.

9 Gaylussite White, also colorless, yellow. Transparent. Mohs' hardness vitreous luster. Density 1.99. Monoclinic, Na 2 Ca(C0 3 ) 2 2 0. Dull,

2'/2-3.

H

10 Phosgenite (also called lead-horn ore) [4 faceted stones] Colorless, white, yellowish, also greenish. Transparent. Mohs' hardness 2-3. Density 6.13. Tetragonal, 1

Silver

Pb 2 (Cl 2

|

C0

3 ).

Greasy, adamantine

luster.

The originally silver- white dendritic inclusions in quartz that have turned

deep black. Opaque. Mohs' hardness

2'/2-3.

Denisty 9.6-12.0. Cubic, Ag. Metallic

luster.

12

Gold 2'/2-3.

1

Pure gold included in quartz. Golden-yellow. Opaque. Mohs' hardness Density 15.5-19.3. Cubic, Au. Metallic luster.

Vivianite Blue-green, also deep blue, colorless. Transparent to translucent. Mohs' hardness Wi-2. Density 2.64-2.70. Monoclinic, Fe 3 (P0 4 ) 2 -8H 2 0). Vitreous to mother-of-pearl luster. Very strongly pleochroism.

14 Sulphur Yellow, also brownish. Translucent. Mohs' hardness Wi-lYi. Density 2.05-2.08. Orthorhombic. S. adamantine luster. Extremely sensitive to heat, bursts

when warmed

15 Prousite

Cinnabar to

5.51-5.64. Trigonal,

when exposed 16 Howlite

in one's hand. scarlet-red. Translucent.

Ag AsS 3

Adamantine

luster.

Mohs' hardness

The

2Vi.

Density

color gradually darkens

to light.

When

colored blue, howlite (see above, no. 2)

imitate turquoise (page 170).

208

3

.

is

occasionally used to

•

i»v

13

wmr

hBHI

m «!{§%

Indigo-blue, also deep blue. Transparent to translucent. Mohs' hardness

Boleite

1

3-3/2. Density 5.05. Tetragonal (pseudo-cubic).

reous luster; on cleavage surfaces mother-of-pearl 2 Oligoclase [3 faceted stones]

Pb 26 Ag 9 Cu 24 (OH) 48 Cl 62

.

Vit-

luster.

Colorless to bluish plagioclase feldspar. Transpar-

Mohs' hardness 6-6/2. Density 2.62-2.67. Triclinic, (Na,Ca)[(Si,Al) 2 Si 2 O g ]. Vitreous luster, on cleavage surfaces mother-of-pearl luster. ent.

3 Ludlamite

Light- to apple-green, colorless. Transparent to translucent. Mohs' hardness 3-4. Density 3.1-3.2. Monoclinic, Fe 3 (P0 4 ) 2 4H 2 0. Vitreous luster. •

4 Adamine

Yellow-green, brownish, also colorless, pink, violet. [2 faceted stones] Transparent to translucent. Mohs' hardness VA. Density 4.30-4.68. Orthorhombic,

Zn 2 (OH

As0 4

|

).

Strong, vitreous

luster.

Augelite Colorless to slightly yellowish. Transparent. Mohs' hardness 4/>-5. Density 2.70-2.75. Monoclinic, Al 2 [(OH) 3 P0 4 ].

5

|

6 Friedelite Pink-red to red-brown. Translucent to opaque. Mohs' hardness 4-5. Density 3.06-3.19. Trigonal, (Mn,Fe) 8 [(OH,Cl) 10 Si 6 15 ]. Vitreous luster. |

cabochons] Gray-green, also pearl-white, blue-green, yellowish. Translucent to opaque. Mohs' hardness 1. Density 2.55-2.80. Monoclinic (pseudohex-

7 Talc

[2

Mg

[(OH) 2 Si 4 O 10 ]. Mother-of-pearl-luster, greasy luster; also dull. Dense aggregates are called soapstone or steatite; they can be easily carved and are worked on the wheel into ornamental objects. agonal),

3

|

Feels greasy.

8 Manganese-Otantalite [3 faceted stones] Scarlet-red to dark red. Transparent. Mohs' hardness 5/2-6/2. Density 7.73-7.97. Orthorhombic, (Mn,Fe) (Ta,Nb) 2 6 Vitreous luster. .

9 Gadolinite Black, also green-black, brown, very rarely pale green. Usually opaque; light varieties are transparent. Mohs' hardness 6V2-I Density 4.00-4.65. Monoclinic, Y2 FeBe 2 (0 Si0 4 ) 2 Vitreous to greasy luster; very brittle. .

.

|

10 Anglesite

Colorless, yellow, also greenish, brownish, white. [3 faceted stones] Transparent to translucent. Mohs' hardness 3-3/2. Density 6.30-6.39. Orthorhombic, Pb(S0 4 ). Vitreous to adamantine luster; brittle.

1

Vlasovite

[3

faceted stones]

Yellow, yellow-brown, also colorless. Transparent.

Mohs' hardness 6. Density 2.97. Monoclinic, Na 4 Zr 2 (0 2 Si 8 O 20 ). Greasy luster; on cleavage surfaces vitreous to mother-of-pearl-luster; brittle. |

Dark green, also yellow, light- to dark brown. Transparent to transluMohs' hardness 4/2— 6/2. Density 3.28-3.32. Originally tetragonal, later amorphous, due to persisting radioactivity, K(Ca,Na) 2 Th(Si 8 O 20 The data of crystalline ekanite is somewhat different from that of the amorphous variety.

12 Ekanite cent.

).

Vitreous

luster. Radioactive!

13 Phosphophyllite [2 faceted stones]

Blue-green, also colorless. Transparent. 4H 2 0. ] 2

Mohs' hardness 3-3/2. Density 3.7-3.13. Monoclinic, Zn 2 (Fe,Mn)[P0 2 Vitreous 14

Gypsum

luster.

•

Perfect cleavage; brittle.

(also called selenite) [2

cabochons] White, yellowish, also colorless, Mohs' hardness 2 Density 2.20-2 .40. Mono-

pink, bluish. Transparent to opaque.

Ca(S0 4 ) • 2H 2 0.

.

Vitreous luster; fibrous aggregates show silky luster. Very sensitive to heat. Gypsum is rock-forming; compare to alabaster, page 222. clinic,

The

illustrations are

210

40 percent

larger than the originals.

#

IvI

ft

2

• 13

1©

12

1

Analcime

Cat's

2

Analcime

[4

Eye

Pink, South Africa. (For

faceted stones]

more

data, see below, no. 2.)

Colorless, white, also pink, yellowish, greenish.

Transparent to opaque. Mohs' hardness S-SVi. Density 2.22-2.29. 3 Triphyline

Brownish, also greenish-gray, bluish-gray. Trans[3 faceted stones] parent to translucent. Mohs' hardness 4-5. Density 3.34-3.58. Orthorhombic, Li(Fe,Mn)[P0 4 ]. Vitreous luster; brittle.

4 Staurolite Reddish-brown, black. Translucent to opaque. Mohs' hardness 1-1 Vl Density 3.7-3.8. Monoclinic. Vitreous Luster. Characteristic interpenetration twinning.

Hornblende [2 faceted stones] Brown-yellow, also green, black. Translucent to opaque. Mohs' hardness 5-6. Density 2.9-3.4. Monoclinic.

5

6 Pectolite [3 faceted stones] Light blue to light green, also colorless, gray. Transparent to translucent. Mohs' hardness 4'/2-5. Density 2.74-2.88. Triclinic, NaCa 2 [Si 3 8 (OH)]. Vitreous to silky luster. 7 Zektzerite [2 faceted stones] cent.

Mohs' hardness

Colorless, also light pink. Transparent to translu-

Density 2.79. Orthorhombic.

6.

8 Nepheline [3 faceted stones] Light pink, also colorless, white, greenish, yellowish. Transparent to opaque. Mohs' hardness 5-6. Density 2.55-2.65. Hexagonal, KNa 3 (AlSi0 4 ) 4 Vitreous luster; on surface of fracture greasy luster. Elaolite is a dull, mostly greenish nepheline variety. .

9 Greenockite [synthetic] Orange, also yellow to brown. Transparent to translucent. Mohs' hardness 3-3 /?. Density 4.73-4.79. Hexagonal, CdS. 1

Anatase

10

faceted stones]

[2

Dark brown, also colorless, yellow, blue, reddish, Mohs' hardness 5'/2-6. Density 3.82-3.97.

black. Transparent to translucent.

Tetragonal,

Ti0 2 Adamantine

luster.

.

Milarite Yellow, also colorless, white, green. Transparent. Mohs' hardness 5'/2-6. Density 2.46-2.61. Hexagonal, KCa 2 AlBe 2 (Si 12 luster. 2 0. Vitreous 30 )

11

O

12 Descloizite

Mohs' hardness lucent.

Whewellite

14 1

H

3-3'/2.

Density 5.5-6.2. Orthorhombic.

Brown, also yellow, blue. Transparent Mohs' hardness 4-5. Density 3.4-3.6. Orthorhombic.

Lithiophilite

1

•

Red-brown, also orange, brown-black. Transparent to translucent.

[2

faceted stones]

Yellowish, faceted. (For

more

to trans-

data, see below, no. 20.)

Jeremejewite [2 faceted stones] Bluish, also colorless, yellowish. Transparent. Mohs' hardness 6V2-IV2. Density 3.28-3.31. Hexagonal, A1B0 3 .

16 Clinohumite

[2

faceted stones]

opaque. Mohs' hardness 1

6.

Orange

to yellow, also white. Transparent to

Density 3.13-3.75. Monoclinic.

Clinzoisite [3 faceted stones]

Yellow to yellow-brown, also colorless, greenish, Mohs' hardness 6-7. Density 3.21-3.38. MonoSi 2 7 ). Vitreous luster.

pink. Transparent to translucent. clinic,

Ca 2 Al 8 (0

I

OH

I

Si0 4

|

cabochons] Brown-red, brown, also pink. Translucent to opaque. Mons' hardness 5-5 V2. Density 2.74-2.98. Trigonal.

18 Eudialite

[2

Black. Translucent to opaque. Mohs' hardness 19 Neptunite [2 faceted stones] 5-6. Density 3.19-3.23. Monoclinic. Strong, vitreous luster.

Colorless, white, yellowish, also brownish. [3 faceted stones] Transparent. Mohs' hardness 2'/2-3. Density 2.19-2.25. Monoclinic, Ca(C 2 4) Vitreous to mother-of-pearl-luster. Whewellite is an organic product. 2 0.

20 Whewellite

•

H

The

212

illustrations are

20 percent

larger than the originals.

# £9

•*

*.*

1

Montebrasite

[5

faceted stones]

also white, pink. Transparent.

LiAl[(OH,F) 2

P0 4

|

Vitreous

].

Colorless, yellowish, light green, light blue, 5 />-6. Density 2 .98-3 1 1 Triclinic,

Mohs' hardness

.

.

luster.

Cinnabar

Red, also pale blue. Translucent to opaque. Mohs' [2 faceted stones] hardness 2-2/2. Density 8.0-8.2. Trigonal, HgS. Adamantine luster.

3 Boracite

Mg

3

[Cl

Light green, also colorless, white, yellow, bluish. Transparent to trans1-lVi. Density 2.95-2.96. Orthorhombic, B 7 13 ]. Vitreous to adamantine luster.

Mohs' hardness

lucent. |

4 Magnesite Colorless, also white, yellow to brown. Transparent to translucent. Mohs' hardness 3/2-4/2. Density 2.96-3.12. Trigonal, MgC0 3 Vitreous to dull .

luster.

5

Wolframite

Black, also dark brown. Translucent to opaque.

5-5/2. Density 7.1-7.6. Monoclinic,

Wolframite

is

mixed

a

(Fe,Mn)W0 4

crystal of ferberite

.

Mohs' hardness

Metallic to greasy

luster.

and hubnerite.

6 Herderite [2 faceted stones] Fallow blue, also colorless, pale green, yellowish. Transparent to translucent. Mohs' hardness S—SVi. Density 2.95-3.02. Monoclinic, CaBe[(F,OH) P0 4 ]. Vitreous luster. |

7

Leucophane parent.

Yellow with needle-like aegirine inclusions, also greenish. Trans4. Density 3.0. Triclinic (Na,Ca) 2 Be[Si 2 6 (F,OH)].

Mohs' hardness

Dark red. Translucent. Mohs' hardness 2/2-3. Density 5.85. Trigo-

8 Pyrargyrite nal,

Ag SbS 3

3

.

Adamantine

luster.

9 Bustamite Light pink, also brown-red. Transparent. Mohs' hardness 5/2-6. Density 3.32-3.43. Triclinic, (Mn,Ca) 3 (Si 3 9 ). Vitreous luster. 10

Magnetite

Black, opaque.

Mohs' hardness

Metallic luster; °trongly magnetic.

The

5/2-6/2. Density 5.2. Cubic, Fe 3

4

.

originally bright black color gradually

changes to dark brown. 1

Strontianite Light yellow, also colorless, white, brown, green, reddish. Transparent to translucent. Mohs' hardness 3/2. Density 3.63-3.79. Orthorhombic, SrC0 3 Vitreous luster; on surface of fracture, greasy luster. .

1

Parisite [3 faceted stones]

Mohs' hardness Vitreous 1

4/2.

Yellow-brown, also redish. Transparent to translucent.

Density 4.33-4.42. Trigonal, Ca(Ce,La) 2 [Fe 2

|

(C0

Eosphorite Yellow-brown, also colorless, pink. Transparent to translucent. Mohs' hardness 5. Density 3.05-3.08. Orthorhombic, (Mn,Fe)Al[(OH) 2 P0 4 |

H 14

3 ) 3 ].

luster.

2

0. Vitreous

Senarmonite

Colorless, also white, gray. Transparent to translucent. Mohs'

hardness 2-2/2. Density 5.2-5.5. Cubic, Sb 2 15 Taaffeite

]

luster.

3

.

Adamantine

luster.

Violet, also colorless, pale green, bluish, pink, red. Transparent.

Mohs' hardness 8-8/2. Density 3.60-3.62. Hexagonal,

Mg

3

Al 8 Be0 16 Vitreous .

luster. 1

Simpsonite

Orange, also

1

Mohs' (OH). Vitreous to

colorless, white, brownish-yellow. Translucent.

hardness 7-7/2. Density 5.92-6.84. Hexagonal, Al 4 (TaNb) 3

adamantine

luster.

Diaspore

Greenish-brown, also

13

colorless, white, yellow, bluish, pink. Transpar-

ent to translucent. Mohs' hardness 6/>-7. Density 3.30-3.39. Orthorhombic, AlOOH. Vitreous luster; on cleavage surfaces mother-of-pearl luster.

2 14

The

illustrations are

40 percent

larger than the originals.

to

6 tt

§ 10

^Rfc

11

12

13

$ 14

15

16

17

1

Thaumasite [3 faceted stones] Mohs' hardness VA. Density

12H 2 0. Vitreous

Colorless, light yellow, also white. Translucent. 1.91.

Hexagonal, Ca 3 [C0 3

|

S0 4

|

Si(OH) 6

•

]

luster.

2 Cancrinite [4 faceted stones, 1 cabochon] Yellow, orange, also colorless, white, bluish, pink. Transparent to translucent. Mohs' hardness 5-6. Density 2.42-2.51.

Hexagonal,

Na 2 Ca 2 [(C0

3 )2

|

AlSi0 4 ) 6

•

]

2H 2 0. Vitreous luster; on cleavage sur-

faces mother-of-pearl luster.

3 Tremolite (also called grammatite) [6 faceted stones, 1 cabochon] Gray-brown, green, also colorless, white, pink. Transparent to translucent. Mohs' hardness 5-6. Density 2.95-3.07. Monoclinic, Ca 2 [(OH,F) Si 4 n ] 2 Vitreous to silky 5

Mg

O

|

.

luster.

4 Yugawaralite [2 faceted stones] Colorless, also dull white. Transparent to translucent. Mohs' hardness 4'/2. Density 2.19-2.23. Monoclinic, Ca(Al 2 Si 6 16) •

4H 2 0. 5

Vitreous

luster.

Sapphirine [2 faceted stones] Dark blue, also colorless, greenish, pink, violet. Transparent. Mohs' hardness l h. Density 3.40-3.58. Monoclinic, (Mg,Al) 8 [0 2 Al,Si) 6 18 ]. Vitreous luster. So named because of its blue color x

|

similar to sapphire.

6 Aegirine— augite Black, also green-black. Transparent. Mohs' hardness 6. Density 3.40-3.55. Monoclinic. Vitreous luster. Aegirin is an augite that is rich in sodium. 7

Melinophane

faceted stones] Honey-yellow, orange, also colorless, Mohs' hardness 5-5'/2. Density 3.00-3.03. Tetragonal (Ca,Na) 2 (Be,Al)[Si 2 6 (OH,F)]. Vitreous luster. [2

yellowish-red. Translucent.

8 Pollucite

(also called

pollux) [3 faceted stones]

bluish, violet. Transparent to translucent.

2.85-2.94. Cubic (Cs,Na)(AlSi 2

6)

•

Colorless, gray, also white,

Mohs' hardness 6V2-I Density .

^O. Vitreous

luster.

9 Andesine

Light pink, also white, gray, yellowish, greenish. Transparent to 6-6'/2. Density 2.65-2.69. Triclinic (Na,Ca)[(Si,Al) 2 Si 2 O g ]. Vitreous to dull luster; on cleavage surfaces mother-ofpearl luster. Perfect cleavage. Andesine belongs to the group of plagioclase feldspars (see page 164).

translucent. Mohs' hardness

10 Legrandite

Yellow, also colorless. Transparent.

3.98-4.04. Monoclinic, 1

Muscovite

Zn 2 (OH

|

As0 4 )

•

H

2 0.

Mohs' hardness 4'/2-5. Density Vitreous luster.

Pink, also colorless, silver- white, yellowish, greenish. Transparent to

translucent. Mohs' hardness 2-3. Density 2.78-2.88. Monoclinic, KAl 2 [(OH,F) 2 AlSi 3 O 10 ]. Vitreous luster; on cleavage surfaces mother-of-pearl luster. Perfect cleavage. Because of its silvery sheen, muscovite is called cat's silver in the vernacular. A chrome-containing muscovite variety, which is green, is called |

fuchsite.

Black. Transparent. Mohs' hardness 5-6. Density 4.5. Triclinic (Ce,La)(Y,U,Fe)(Ti,Fe) 20 (O,OH) 38 Metallic luster.

12 Davidite

.

13 Mesolite 5-5'/2.

Colorless, also white. Transparent to translucent.

Mohs' hardness

Density 2.26-2.40. Monoclinic (pseudo-orthorhombic),

Na 2 Ca 2 (Al 2 Si

3

O

10 ) 3

•

8H 2 0.

Vitreous to dull

luster.

14 Pyrolusite Black, also dark gray. Transparent. Mohs' hardness 6-7. Density 4.5-5.0. Tetragonal, Strong metallic luster. Color can rub off on fingers. 2

Mn0

The

216

.

illustrations are

50 percent

larger than the originals.

L

o i(

w

Rocks as Gemstones Formerly, rocks were used almost exclusively for decorative purposes and for ornamental objects. Nowadays, rocks are becoming more and more important also for personal jewelry, especially for costume jewelry. (Refer also to page 69.)

Onyx Marble

[1,

2]

Also called Marble Onyx

Color: Yellow-green, white, brown, striped Color of streak: According to color of stone

Composition: Calcite or aragonite Transparency: Translucent to opaque

Mohs' hardness: 3V2-4 Density: 2.72-2.85

Refractive index:

The

Double

1.486-1.686

-0.156 to -0.172

refraction:

offered in the trade as onyx marble

is a limestone formed by the must not be confused with chalcedony-onyx (page 142). It is incorrect to name this rock onyx without the addition of the word marble. Onyx marble is formed from lime-containing water by layered deposits (therefore

rock that

is

minerals calcite or aragonite.

It

always banded) near warm springs or as stalactites or stalagmites in caves. Deposits are

found in Egypt, Algeria, Argentina, Morocco, Mexico, and the United used for ornamental objects such as pendants and brooches. Possibilities for

Confusion

With

States. It

the mineral serpentine (page 202) as well as with

various serpentine rocks, especially with the green-white spotted

Connemara from

Connaught, Ireland (compare with page 202) or with the banded, greenish from New Mexico, United States.

Mexican onyx

called Aragonite Sinter

Color: White, yellow, brown, reddish Color of streak: According to color of stone

Composition: Aragonite Transparency: Translucent, opaque

1.530-1.685 Double refraction Aragonite -0.155

Refractive index: Aragonite

Mobs' hardness: 31/2-4 Density: 2.95

is

ricolite

Misleading trade name for onyx marble.

Tufa [5-7] Also

Tufa

is

:

from hot springs in the form of encrustations or wavy layers. The best known occurrence is at Karlsbad (Karlovy

the calcium carbonate deposit

stalactites,

often with

Vary) in Czech Republic. Other deposits are found in Argentina, Mexico, Zealand, Russia, and the United States.

Landscape Marble

[8]

New

Also called Ruin Marble

fine-grained limestone, where the layers have been fractured, displaced, and again solidified. Because of the different coloring of the individual layers, images are formed which convey the impression of a landscape. It is used as a decorative stone,

This

a

is

also for

brooches or pendants, cut en cabochon. The landscape marble shown on the make one think of skyscrapers in a metropolis with low, thundery clouds.

right could

Onyx Onyx 3 Onyx 4 Onyx 1

2

The

218

marble, marble, marble, marble,

bowl broken piece, 2 pendants

partly polished

figurine

illustrations are

50 percent smaller than the

5 Tufa, 2 pieces from Karlsbad, Bohemia 6 Tufa brooch and pendant 7 Tufa, New Mexico, U.S. 8 Landscape marble, Tuscany Italy originals.

K

/

t,

Orbicular Diorite [1, 2] Also called Ball Diorite Plutonic rock composed of feldspar, hornblende, biotite, and rythmic crystallization which produces

Used

spherical shapes.

a

quartz.

Formed by

separation of light and dark marerials into

en cabochon [no.

as a decorative stone, also cut

2].

Kakotokite Trade name for

a

black-white-red banded nepheline-syenite from Greenland, con-

taining eudialyte.

Obsidian [3-7] Color: Black, gray,

brown, green

Transparency: Opaque, translucent

Color of streak: White Mohs' hardness: 5-5# Density: 2.35-2.60 Cleavage: None Fracture: Large conchoidal, sharp edged

Pleochroism: Absent Absorption spectrum: Cannot be evaluated

Composition: Volcanic, amorphous, siliceous

Fluorescence:

Refractive index: 1.45-1.55

Double

refraction:

None

Dispersion: 0.010

None

glassy rock

Obsidian (named after the Roman, Obsius) was used in antiquity for amulets and necklaces. Varieties show golden [Gold o., no. 4] or silver [Silver o., no. 5] sheen, caused by inclusions. Deposits are found in Ecuador, Indonesia, Iceland, Italy, Japan, Mexico, and the United States. Possibilities for Confusion With aegirin-augite (page 216), gadolinite (page 210), gagate (page 226), hematite (page 162), pyrolusite (page 216), and wolframite (page 214).

Snowflake obsidian [6, 7] Trade name for an obsidian with gray-white, ballshaped inclusions (spherulites). Deposits are found in Mexico and the United States.

Moldavite [10-12] Also Color: Bottle-green to

called Bouteille Stone,

brown-green

dioxide

Color of streak: White Mohs' hardness: SVz Density:

Refractive index: 1.48-1.54

Double

None

refraction:

Pleochroism: Absent Absorption spectrum: Cannot be evaluated

Amorphous

Chemical composition: Si0 2 (

None

None

Dispersion:

Fracture: Conchoidal Crystal system:

oxide)

Transparency: Transparent to opaque

2.32-2.38

Cleavage:

Water Chrysolite

+ (aluminum

+ Al 2

3 ) silicon

Fluorescence:

None

Moldavite (named after Moldau, Czech Republic) belongs to the Tektite group; formed from condensed rock vapors after being hit by a meteorite. Scarred surfaces; vitreous luster. Possibilities for

Confusion

With

apatite (page 194), diopside (page 190), precious

beryl (page 96), sapphire (page 86), tourmaline (page 110), and with green bottle glass. Other tektites are dark brown to black [8, 9]. Depending on the place of discovery, they have different names, e.g., Australite (Australia), Billitonite (Borneo), Georgiaite

(Georgia, United States), Indochinite (Indochine), Javaite Qava), and Philippinite (the Philippines). 1

8 Tektite, rough, Thailand 9 Tektite, 2 faceted stones, Thailand 10 Moldavite, 4 rough pieces,

Orbicular diorite, partly polished, Corsica

2 Orbicular diorite, cabochon,

Czech Republic

Corsica 3 Obsidian, rough, Mexico 4 Golden obsidian, Mexico 5 Silver obsidian, Mexico

6 Snowflake obsidian, 2 cabochons 7 Snowflake obsidian, partly polished The illustrations are 40 percent smaller than the

220

1

1

Moldavite, 6 faceted stones,

Czech Republic 12 Moldavite, cabochon, Czech Republic originals.

4 10

^^

Alabaster [1,2] Color: White, pink, brownish Color of streak: White Mohs' hardness: 2

hydrous calcium sulphate Transparency: Opaque, translucent at edges

Density: 2.30-2.33

Double

Chemical composition: Ca(S0 4 )-2H 2

Dispersion: 0.033(0.008)

Alabaster (from Greek)

is

Refractive index:

1.520-1.530

refraction:

+0.010

the fine-grained variety of gypsum; in antiquity, the

name

also referred to microcrystalline limestone. Deposits are

found in Thuringia, England (Derbyshire), France (Parisian Basin), Italy (Tuscany), and the United States (Colorado). Used for ornamental objects, rarely as jewelry. Can easily be dyed because of

its

porosity.

Possibilities for

gypsum (page

Confusion With agalmatolite (see below), calcite (page meerschaum (see below), and onyx marble (page 218).

208),

210),

Agalmatolite Also

called Picture Stone, Pagoda Stone, Pagodite Whitish, greenish, or yellowish, dense aggregate of the mineral pyrophyllite; Al 2 [(OH) 2 Si 4 O 10 ]. When heat-treated, the originally soft stone (Mohs' hardness 1-1 Vi) hardens considerably. Deposits are found in Finland, Slovakia, South Africa, and the United States (California). Usage as for alabaster (see above). |

Possibilities for ish variety

is

Confusion

With alabaster (see above),

used to imitate jade (page

Meerschaum

talc

(page 210).

The green-

154).

[3-5] Also called Sepiolite

Color: White, also yellowish, gray, reddish

*

Color of streak: White Mohs' hardness: 2-2 /2 Density: 2.0-2.1 Cleavage: Perfect Fracture: Flat conchoidal, earthy Crystal system: Orthorhombic;

Mg 4 [(0H) 2

hydrous magnesium

silicate

Opaque

Refractive index: 1.53

Double refraction: None Dispersion:

None

Pleochroism: Absent Absorption spectrum: Cannot be evaluated Fluorescence: None

microcrystalline

Chemical composition:

6H 2

Transparency:

1

I

Si 6

15 ]

Because of its high porosity, meerschaum can float (German — sea foam). It occurs as a rock as concretion in serpentine. It has a dull greasy luster, feels like soap, and sticks to the tongue. The most important deposit is near Eskischehir, Anatolia (Turkey). It is also found in Greece (Samos), Morocco, Spain, Tanzania, and the United States (Texas). Worked into bowls for pipes and cigarette holders, which, because of the smoke, gradually become golden-yellow [no. 5]; in addition, it is used for costume jewelry. Becomes lustrous when impregnated with grease. Can be confused with alabaster (see above).

Fossils [6-9] Petrified

wood pieces (page

148) and other fossils (petrified animals or parts of animal)

making jewelry because of their form, structure, color, For more about their formation, see page 148.

are attractive for

old age.

1

Alabaster, 2 pieces dyed red

2 Alabaster asktray, dyed blue

3 Meerschaum, 4 Meerschaum, 5 Meerschaum, The illustrations

222

rough

costume jewelry

6 Ammonite,

shell

Ammonite,

shell

replaced by pyrite replaced by pyrite, partly polished 8 Trilobite, primeval crab in shale 9 Actaeonella, a sea snail, Austria, partly polished 7

cigarette holder

are

as well as their

20 percent smaller than the

originals.

LM

Organic Gemstones A number of gemstones

are of organic origin, but have the quality and character of

stones. Refer also to the description

on page

69.

Coral Color: Red, pink, white, black, blue

Transparency: Translucent, opaque

Color of streak: White Mohs' hardness: 3-4

Refractive index:

Density:

White and

Cleavage:

red:

2.60-2.70

None

-0.172 None Pleochroism: Absent to

Fracture: Irregular, splintery, brittle

Crystal system: (Trigonal) microcrystalline

Chemical composition: substance

Most

White and red: 1.486-1.658 Double refraction: White and red: -0.160

CaC0 3

or organic

Dispersion:

Absorption spectrum: Cannot be evaluated Fluorescence:

Weak;

violet

(name of Greek origin) have built reefs and atolls with their branching Only their calcified skeletons are used as gemstone material; they are formed

corals

trunks.

by tiny polyps. The height of the branches is the branches are up to 2Vi in (6 cm) thick.

in the general range

8-10

in

(20-40 cm);

Deposits are found along the coasts of the Western Mediterranean countries, the Sea, Bay of Biscay, Canary Islands, Malaysian Archipelago, the Midway Islands, Japan, and Hawaii (United States). The coral is found at depths of 1-1020 ft (3-300 m), and mainly harvested with weighted, wide-meshed nets dredged across the seabed. When harvested by divers, however, not as many corals are damaged. Near Hawaii, minisubmarines have recently been used to collect the coral. When it is brought to the surface, the soft parts are rubbed away and the material is sorted as to quality. For more than 200 years, the main trade center has been Torre del Greco, south of Naples, Italy. Still threequarters of the corals harvested all over the world are processed here. Unworked coral is dull; when polished it has a vitreous luster. It is polished with fine-grained sandstone and emery; finely polished with felt- wheels. It is used for beads for necklaces and bracelets, for cabochons, ornamental objects, and sculptures. Branch-like pieces are pierced transversely and strung as spiky necklaces [no. 13]. Corals are sensitive to heat, acids, and hot solutions. The color can fade when worn.

Red

Confusion With conch pearl (page 233). cornelian (page 126), rhodonite (page 168), and spessartine (page 104). Imitations are made from glass, horn, rubber (gutta-percha), bone, and plastics. Since the 1970s, good imitations exist. Possibilities for

Noble coral (Corallium rubrum) Most desired of all coral types. According to place it has numerous trade names. The color is uniform: light red to salmoncolored (Momo), medium red (Sardegan), ox-blood-red (Moro), tender pink with

of discovery,

whitish or light-reddish spots (Angels' Skin Coral [no.

Black coral

11]).

Consists of an organic horn substance. In the world trade

it is,

as

with

blue corals, of no economic importance.

1

Noble

coral, 3

8 White 9 Noble 10 Noble 1 1 Noble 1 2 Noble

beads together 23.77ct

2 Noble coral, branch, Sicily 3 Noble coral, 2 figurines, Japan 4 Noble coral, 5 cabochons 5 Noble coral, 2 necklaces 6 Noble coral, figurine, Japan 7 White coral, branches, Japan The illustrations are 50 percent smaller than the

224

1

3

White

14 Black originals

coral, 2

engraved beads

engraved, Italy coral, branch, Japan coral, 3 cabochons, 14.05ct

coral,

coral, figurine, Italy

coral, spiky

necklace

coral, branch, Australia

Gagate

Also called Jet

[7, 8]

Deep black, dark brown Color of streak: Black-brown Mohs' hardness: 2^-4 Density: 1.19-1.35

Transparency:

Color:

Cleavage:

Double

None

1.640-1.680

None

refraction:

Dispersion:

None

Pleochroism: Absent Absorption: Cannot be evaluated Fluorescence: None

Fracture: Conchoidal

Chemical composition: Lignite

Gagate (named

Opaque

Refractive index:

after a river in

Turkey)

is a

bituminous coal which can be polished.

It

has a velvety, waxy luster. Deposits are found in Wurttemberg (Germany), France (Dep. Aude), Poland, Spain (Asturia), and the United States (Colorado, New Mexico, Utah).

It is

objects,

worked on

a lathe.

Used

for

mourning

jewelry, rosaries,

ornamental

and cameos.

Possibilities for

With anthrazite,

Confusion

(page 142), schorl (page

110).

onyx rubber (gutta-percia),

asphalt, cannel coal (see below),

Some imitations made with

glass,

plastic.

Cannel coal [6] The name is derived from the English "candle," referring to the wax that was extracted from combustible-rich layers in coal seams; formed predominantly from plant spores and pollen. Deposits are found in North Rhine-Westphalia (Germany), England, and Scotland. Due to its homogeneity and density, it can be easily worked on the lathe; a high luster can be achieved through polishing. Serves as substitute for gagate.

Ivory [1-5,

9]

Color: White,

creamy

Color of streak: White Mohs' hardness: 2-3 Density: 1.7-2.0 Cleavage: None Fracture: Fibrous Chemical composition Calcium phosphate

Transparency: Translucent, opaque Refractive index:

Double refraction

1.535-1.570 :

None

None Pleochroism: None Dispersion:

Absorption spectrum: Cannot be evaluated Fluorescence: Various blues

Ivory originally only referred to the material of the elephant's tusk. Today it is also the teeth of hippopotamus, narwhal, sea lion, wild boar, and fossilized mammoth. Most comes from Africa, some from Burma (Myanmar), India, and Sumatra. Since 1989, there has been a worldwide ban on any trade in elephant's ivory. Worked with cutting tools and file, it can be dyed. Used for ornamental objects, pendants, and for costume jewelry. Can be confused with many types of bone [no. 10].

Odontolite (Also called tooth turquoise) Odontolite (Greek — toothstone) is fostooth or bone substance from extinct prehistoric large animals (such as the mammoth, mastodon, or dinosaurs). Dyed turquoise blue with viviantite (page 208). Deposits are found in Siberia and the south of France. Has become very rare. Can be confused with turquoise (page 170) and ivory that has been dyed blue (see above). silized

1

Ivory,

7 Gagate, 3 faceted pieces 8 Gagate, 2 cabochons 9 Ivory, brooch, China 10 Bone, dyed, Israel

concentric spheres, China

2 Ivory, figurine

and bowl

3

Ivory,

4

Ivory,

rough, Congo necklace, China

5

Ivory,

bracelet

and

figurine

6 Cannel coal, rough and partly polished

The

illustrations are

226

50 percent smaller than the

originals.

Amber Also

called Succinite

and also other colors Color of streak: White Mohs' hardness: 2-2 Vi Density: Mostly 1 .05-1 .09 Cleavage: None Fracture: Conchoidal, brittle Crystal system: Amorphous Chemical composition: Approximately C10H16O fixture of various resins

Color: Yellow, brown,

Transparency: Transparent to opaque Refractive index:

Double

1.539-1.545

refraction:

Dispersion:

None

None

Pleochroism: Absent Absorption spectrum: Cannot be evaluated Fluorescence: Bluish-white to yellow-green Burmite: blue

Amber is the fossilized, hardened resin of the pine tree, Pinussuccinifera, formed in the Eocene epoch of the Tertiary period, about 50 million years ago; found mostly in the Baltic, although younger ambers are known from the Dominican Republic. Mostly amber is drop or nodular shaped with a homigeneous structure, or has a shell-like formation, often with a weathered crust. Pieces weighing over 22 lb (10 g) have been found. It is often turbid because of numerous bubbles [no. 8], fine hair lines, or tension

from the material by Yellow and brown are predominant colors. There are occasional inclusions of insects or parts of plants (called inclusions [no. 7], and illustration on page 50) and of pyrites. Amber is sensitive to acids, caustic solutions, and gasoline, as well as alcohol and perfume. Can be ignited by a match, smelling like incense. When rubbed with a cloth, amber becomes electrically charged and can attract small particles. It has a vitreous fractures. It

is

possible to clear air bubbles and enclosed liquids

boiling in rape-seed

luster;

when

it is

oil.

polished, a resinous luster.

Deposits The largest deposit in the world is in Samland near Palmnicken, west of Konigsberg (Kaliningrad) formerly eastern Prussia (today Russia). Under 100 ft (30 m) of sand is a 30 ft (9 m) layer of amber-containing clay, the so-called blue earth. It is mined from the surface with dredging chain buckets. First the amber is washed out, then picked by hand. Only 15 percent is suitable for jewelry. The remainder is used for pressed amber (see Ambroid below) or used for technical purposes. There are large reserves on the seabed of the Baltic. After heavy storms, amber is found on the beaches and in shallow waters of bordering countries. This sea amber is especially solid and used to be regularly fished for by fishermen. Further deposits are found in Sicity/Italy (called Simetite), Rumania (Rumanite), Burma (Myanmar), China, the Dominican Republic, Japan, Canada, Mexico, the United States (Alaska,

New Jersey). Amber has been used since prehistoric times for jewelry and religious objects, The Baltic amber, the "gold of North," is the earliest-used gem material of all. Used today for ornamental

Uses

accessories for smokers, also as amulets, and mascots.

the

objects, ring stones, pendants, brooches, necklaces,

and bracelets.

Confusion With citrine (page 120), fluorite (page 198), meeronyx marble (page 218), sphalerite (page 200), ambroid (see below). Imitated by newly created resins (copal), other synthetic resins, and yellow Possibilities for

schaum (page

222),

glass.

Ambroid

Natural-looking pressed amber made from smaller pieces and the remains of the genuine amber. These bits are welded at 284-482 degrees F (140-250 degrees C) and 3000 atmospheres pressure into a substance that can be easily mistaken for natural amber.

Amber, rough Amber, partly polished 3 Amber, 3 cabochons 4 Amber, 2 bead necklaces 1

2

228

5 Amber, 6 Amber, 7 Amber, 8 Amber,

2 baroque necklaces various colors

with insect inclusion with bubble inclusion

m w

)

Pearl Color: White, pink,

silver-, cream-, goldencolored, green, blue, black Color of streak: White Mohs' hardness: IVi-A^A Density: 2.60-2.85 Cleavage: None

Transparency: Translucent to opaque Refractive index: 1.52-1.66 Black: 1.53-1.69 Double refraction: -0.156

Dispersion:

None

Pleochroism: Absent Absorption spectrum: Cannot be evaluated Fluorescence: Weak, cannot be evaluated

Uneven

Fracture:

Crystal system: (Orthorhombic)

Genuine black

microcrystalline

Chemical composition: Calcium carbonate + organic substances + water

River-p.

:

p.

Strong

:

Red to reddish pale green

:

Pearls are a product of mussels (bivalve mollusks mainly of the oyster type, family Ostreidae,

which

wing mussels),

rarely of snails.

mainly calcium carbonate

is

They are built up of mother-of-pearl

(in the

form of

(nacre),

aragonite), and an organic

horn

substance (conchiolin) that binds the microcrystals concentrically around an irritant. Although the Mohs' hardness is only IVi-Wi, pearls are extraordinarily compact,

and

it is

The

very

difficult to

(Latin— perna) or from

The

size

its

name

pearl

454ct (1814 grains

=

is

uncertain, but

spherical shape (Latin

of pearls varies between

ever found (called the

The

crush them.

derivation of the

a

may be from

pin head and a pigeon's &gg.

Hope Pearl after a former owner) is 2 90.8 grams);

it is

in

typical pearly luster, also called

a

type of

shell

— sphaerula). The largest pearl

cm) long and weighs the South Kensington Museum in London. enamel or orient luster, is produced by the in (5

overlapping platelets of aragonite and film of conchiolin nearer to the pearl surface. also causes the refraction of light and the resulting colors that can be observed on the pearl surface. The color of pearl varies with the type of mullusk and

This formation the water, and is

is

dependent on the color of the upper conchiolin layer. becomes spotty.

If the conchiolin

irregularly distributed, the pearl

Formation Pearls are formed by sea mussels, some freshwater mussels, and rarely by some snails. They are formed as a result of an irritant that has intruded into the shell of the mussel and the mantle or into the interior of the mantle. The outer skin of this mantle — the epithelium — normally forms the shell by secretion of mother-ofpearl, and also encrusts all foreign bodies within its reach. And such an encrustation will develop into a pearl. If a pearl is formed as a wart-like growth on the inside of the mussel shell, it must be separated from the shell when it is collected. Therefore, its shape

is

always semi-spherical.

It is called blister

or shell pearl. In the trade they

sometimes complement these with mother-of-pearl pieces shaped to form complete spheres.

1

9 6 baroque pearls, 35.7 1ct 10 10 baroque pearls, Biwaco

Mother-of-pearl shell with cultured pearl

2 Pearl necklace, Biwaco cultivation,

cultivation

baroque

1

3 Pearl necklace,

4 chokers,

1

white

4

Pearl necklace,

baroque

5 Pearl necklace, Biwaco cultivation,

graduated

16 6 black baroque pearls Pearl necklace, black baroque 18 6 gray pearls, 17.28ct

6 4 baroque pearls 7 Pearl,

Mabe

cultivation, silver-white,

1

20mm 8

Pearl,

The

Mabe

cultivation, gray, oval

illustrations are

230

60 percent smaller than the

Mother-of-pearl, 2 cut pieces

Pearl choker, gray 13 3 pearls, Biwaco cultivation, 29.67ct 14 4 cultured pearls, 16.1 6ct Pearl necklace, choker, gray 1

silver

originals.

When a foreign body enters the inner part of the mantle — the connective tissue — immunity defense. The which has been drawn into the connective tissue together with the foreign body, forms a pearl sac around the intruder and isolates it by secretion of nacre. As we now know, the nacre can also produce a pearl without any foreign body. It is sufficient that a part of the epithelium may for any reason (for instance, an injury from the outside) be drawn into the connective tissue of the mantle.

the mussel forms a nonattached, rounded pearl as a type of epithelial tissue,

Genuine Pearls Genuine pearls are those pearls that come into being in nature, without intervention by human beings, in the ocean as well as in freshwater. Sometimes they are also called natural pearls.

Sea Pearls Pearl-producing sea mollusks live along long stretches of coast at a depth of about 50-65 ft (15-20 m). They are as large as an outstretched hand; their life span is about 13 years. Their habitat is the warmer regions on both sides of the equator. The most important occurrences yielding the best qualities (rose and creamy white) have long been those in the vicinity of the Persian Gulf. Because of this occurrence, all natural seawater pearls, wherever they come from, are called "oriental pearls" in the trade. Also, in the Gulf of Manaar (between India and Sri Lanka) there are ancient beds (pearls of pink-red and soft yellow color), but the pearls are mostly small (so-called seed pearls). Other important occurrences are along the coasts of Madagascar, Burma (Myanmar), the Philippines, many islands in the South Pacific, northern Australia, and the coastal lines of Central America and northern South America. In Japan, the most important country of pearl production, there are only some small beds with natural pearls. Pearls are harvested by divers. Formerly women did the work, without any special tools; today the work is done with the most modern diving gear. Only every 30th or 40th oyster contains a pearl. In Sri Lanka in 1958, dragnets were experimentally used; the result was catastrophic, as the next growth was almost completely destroyed.

The trumpet

snail

{Strombus gigas)

is

the best

known

product (called conch or pink pearl) has porcelain. Commercially it is not important. pearls. Its

Cross section of pearl formation

in

a

of the snails that produce

silky

sheen that resembles

the mantle area of a pearl mollusk.

Cross section

Pearl

S

= Outer

layer of shell

= Mother-of-pearl E a = Epithelium P

232

layer

E,

E,

=

+

Inner epithelium B

+

E,

= Mantle

Very

skilled

hands are required

for the setting of a

bead

into the pearl mussel.

River Pearls Fishing for pearls in freshwater, the river pearls, is today of no great importance commercially; they are rarely of good quality. During the Middle Ages and just after, fishing for pearls in the rivers, which are low in lime and rich in oxygen, of Central Europe as well as in rivers of similar habitats in Asia and North America was of some importance. In Europe, fishing for pearls was the absolute privilege of princes; fished pearls had to be delivered to the ruler personally. Because of pollution of the water, pearl mussels have not flourished or become extinct. Even though the supply in some rivers has partially regenerated due to the improvement of water quality, their existence continues to be threatened because of elevated nitrate levels in the water. In the Scandinavian countries and in Central Europe, pearl mussels are environmentally protected; pearl fishing

is forbidden.

Cultured Pearls The increased demand

for pearls has led to their cultivation in large quantities.

Such

cultured pearls are not an imitation, but a natural product which has been produced with human assistance. Today cultured pearls amount to 90 percent of the total pearl trade.

There

are cultured-pearl farms in the ocean as well as in freshwater rivers.

Seawater cultured pearls The principle behind pearl culturing is simple. Humans cause the mollusk to produce a pearl by insertion of a foreign body (compare formation of the pearl, page 230). In China as early as the 13 th century, small objects were fixed to the inner wall of a mollusk shell so that they would be covered with pearl material. Round pearls were first produced, it is thought, by the Swedish naturalist Carl von Linne (Linnaeus), in 1721 in river mussels.

Modern cultivation of round pearls is based on the experimental work of the German zoologist F. Alverdes, as well as the Japanese, T. Nishikawa, O. Kuwabara, T Mise, and K. Mikimoto, in the second decade of this century. To stimulate the mollusks to produce pearls, rounded mother-of-pearl beads from the shell of the North American freshwater mussel are at first wrapped with a piece of tissue from the mantle of a pearl mollusk {Pinetada martensi), and are then inserted into the cell lining of the mantle of another pearl mollusk.

233

The

inserted tissue continues to

pearl material

is

secreted.

grow and

has the effect of

a pearl sac in

which

The most important element in the production of a pearl is

the tissue, not the foreign body. It has been proven that one can do without the bead, but then the process will not remain economical since the culture of a large pearl takes too much time.

Only one pearly

luster.

layer of nacre

is

necessary for the bead to acquire the characteristic

Since 1976, coreless pearls from the Pacific have been on the market;

they are called Keshi pearls in the trade. It has been an ongoing technical dispute whether these are genuine natural pearls, as the people who offer them claim, or whether they are products of new cultivations. The insertion of the bead into the mollusk requires agile, skilled hands; commonly, this job is filled by women. They operate on 300 to 1000 oysters a day. The normal size of a bead (0.24-0.27 in/6-7 mm) requires a three-year-old mollusk; for smaller beads, younger mollusks can be used. When the bead is greater then 0.35 in (9 mm), the mortality rate of the oysters rises to 80 percent.

Prepared mollusks are kept underwater in the bay in wire cages or, preferably nowadays, plastic cages are suspended at a depth of 6'/2-20 ft (2-6 m) and hung from bamboo floats or ropes which are fixed to buoys. Several times a year the mollusks and their cages must be cleaned and freed from seaweed and other deposits. Their natural enemies are fishes, crabs, polyps, and various parasites — mainly a zooplankton which appears in large quantities like a "red tide" and endangers a whole cultivation farm because it consumes large quantities of oxygen.

Mussel cages must always be supervised and several times a year cleaned of seaweed and other unwanted deposits.

234

Rafts of cultivated pearl farms

in

an ocean bay

in

southern Japan.

The temperature of the water has a great influence on the growth of the mollusks; F (11 degrees C). If the temperature suddenly

the Japanese variety dies at 51 degrees

falls before the winter, the floats with the submerged burden must be dragged from northern farms to warmer waters. The yearly growth rate of the pearl layer surrounding the bead in Japan used to be 0.09 mm; it has now reached 0.3 and is said to be 1.5 in southern seas. Some cultivation farms have been transferred from bays to the open sea, as it was thought that the water current would activate the mollusks to produce faster, with better shapes. At the same time, the bays with their innumerable floats would be less crowded and conditions improved for other pearl mollusks. The mollusks remain in the water for three to four years; by then, the layers around the bead are about 0.8-1.2 mm. If they remain longer in the water, there is a danger that they will become ill, die, or mar the shape of the pearl. No mother-ofpearl is secreted after the 7th year. A mussel can usually be used only once. After the pearl has been removed, most of them die. Accordingly, it is important to make sure that there is sufficient aftergrowth. Cultured pearls with a very thin shell are considered to be of inferior quality. The best times for harvesting in Japan are the dry winter months, November to January, as the secretion of the mother-of-pearl is halted and an especially good luster is present. The pearls are taken from the mollusks, washed, dried, and sorted according to color, size, and quality. The whole production yields roughly 10 percent for good-quality jewelry; 60 percent are of minor quality, and 15-20 percent are rejected. In order to improve and/or change the colors, cultured pearls are treated in various ways, such as bleaching, dyeing, or with radiation. Occasionally, the color is also influenced by insertion of colored cores. Colors that are achieved through radiation are not always permanent.

mm

mm

235

The

Japanese farms were founded in 1913 in southern Honshu; today there 1956, pearls of good quality have been grown in coastal waters of northern and western Australia, as well as cultured blister pearls with a diameter of 0.6- 1 in (15-22 mm), called Mabe pearls in the trade. Today, numerous farms exist in South-Southeast Asia, among others in southern Burma, Malaysia, and Indonesia. first

some on Shikoku and Kyushu. Since

are also

Cultured Freshwater Pearls Since the 1950s there has been a freshwater pearl farm in the Biwa Lake (Japanese — biwaco), north of Kyoto on Honshu, Japan. Pieces of tissue measuring mm, usually without solid beads, are inserted into the freshwater mussels {Hyriopsis schlegeli). As these mussels are very large (8 x 4.3 in/20 x 11 cm), ten insertions can be made into each half and, sometimes, an additional one with a mother-of-pearl bead. For each insertion a sac with pearl is formed. After one to two

4x4

mm) large, but rarely round. Therefore, they are taken out of the mussel, covered with new tissue, and inserted into the same or another mussel to improve the shape. Biwaco cultured pearls reach a diameter of 0.5 in

years the pearls are already 0.24-0.28 in (6-8

(12

mm), but

The

rarely have a perfect

round shape.

of a freshwater mussel is 13 years, but after the operation it produces mother-of-pearl only for 3 more years. Many mussels can be harvested three times. life

Cultivation methods are the same as for the sea mollusks. Cages are

hung on

a

about 3—6/2 ft (1-2 m) depth. The success rate is about 60 percent, clearly higher than in seawater, probably because there are fewer dangers in

bamboo frame

at

which is Biwa Lake.

Since the beginning of the 1970s, freshwater pearls are also cultivated in China. are brought onto the market now in large quantities. But their quality is not as

They good

A

as that

skilled

236

eye

is

of the Japanese cultured pearls.

necessary for the sorting and quality evaluation of pearls.

Pearls are drilled in

that

damaged

such a

way

or less perfect

spots "disappear" at the

same

time.

Use and Valuation of Pearls Pearls have been regarded as one of the most valuable gem materials. They have been used for adornment for 6,000 years. In 2500 B.C., there was a substantial pearl trade in China. Pearls are also popular because they do not require any processing; in their natural state they

show

their full gloss, the de-

sired luster.

As much

as

70 percent of

all

pearls are strung and

worn

The

as necklaces.

usual

same one speaks of a choker; if they are graduated in size with the biggest in the middle and the smallest at the ends, one speaks of a sequel of the necklace or of a length

is

about

15

1

/'

in (40 cm).

Double lengths

are called sautoirs. If pearls of the

size are used,

The

chute.

combination,

done by

collars,

is

Uses

A point

the careful selection of the pearls for necklaces or

i.e.,

eye.

of the pearl, which either has

drilling a hole, thus eliminating the

a

mark or

is less

perfect,

is

chosen for

The diameter of the drill hole, according to mm. To fix the pin for earrings, needles, and

mark.

international agreement, should be 0.3

rings, a drill hole to the depth of two-thirds or three-quarters of the pearl's diameter should suffice. Blue pearls should never be drilled, as they may change color when air reaches the drill hole.

Spotted or damaged pearls can be peeled, i.e., the outer layer can be removed. Badly damaged parts can be cut away; the remaining part is traded as half or threequarter pearl (not to be confused with blister pearls). They are used mainly for earrings and brooches. For decades, the United States has been the largest buyer of cultured pearls.

The

Valuation valuable called

Pearls

is

pearl

is

valued according to shape, color,

the spherical shape.

Those

flattened

bouton (French — button) or button

worn

in a necklace take

on

size,

and

luster.

on one side or half-spherical

pearls; irregular pearls are

the shape of a

little

barrel;

The most pearls are

baroque

pearls.

one speaks of barrel

pearls.

Fair-skinned women in Europe and the United States prefer rose color; darkhaired ladies prefer cream-colored pearls. Pearls are weighed in grains (1 grain 0.05 g = 0.24ct or A carat), and today increasingly in carats. The Japanese weight of mom?ne (= 3.75 g = 18.75ct) is l

becoming rarer in European trade circles. The pearl is evaluated as follows: the weight is multiplied by itself, which is called "once the weight." This is then multiplied by a base price which takes into account the quality and all other factors. It can be 1, but also be 40. For necklaces and collars, where a large number of matched pearls are required, the base price tends to be very high.

237

The word pearl without addition should pearls

must be designated

only be used for natural pearls. Cultured

as such.

Taking Care of Pearls is an organic substance, it is prone to change, especially to drying This can lead to an "aging" of the pearls, limiting their useful life. At first they became dull, then fissures occur, and finally the beads spall. There is no guarantee possible for the life span of a pearl; on average, one estimates 100 to 150 years. But there are pearls which are some hundreds of years old and still look their best. Proper care can certainly preserve and extend the life of pearls. Extreme dryness and moisture are damaging; pearls are also sensitive to acids, perspiration, cosmetics, and hair spray. Regular examination and maintenance by a firm specializing in pearls can also prolong their life. Since pearls have a low hardness, they can be easily scratched. Therefore, wear and

Since conchiolin

out.

store

them

in

such a way that the pearl surface

is

never in contact with metal.

Discerning Pearls from Imitations is the case for all gemstones, there are numerous imitations of pearls on the market.

As

To

recognize these

is

important

just as

cultured pearls, because there

Differentiating

is

a

as the differentiation

huge disparity

Between Natural and Cultured

Pearls

difference in the appearance of natural and cultured pearls.

them

is

between natural and

in respective prices.

To

There

all)

little

Their density can help, as it is greater than 2.73 in cultured pearls, while the density of natural pearls in usually lower.

difficult.

(but not

or no between the case of most is

differentiate

Sometimes an examination with can

clarify.

Under

certain radiation

ultraviolet light, for instance, cul-

tured pearls have a yellow luminescence, and under X rays a green one. One reliable method of differentiating between cultured and natural pearls

is

by examin-

ing their inner structure. Natural pearls have a concentrically layered structure, while the inner structure

of the cultured pearl varies according to the type of bead. Typically, an expert uses an instrument like an

endoscope to explore the structure of the pearl inside the drilling hole.

of a cultured

Natural and cultured pearls distinguish themselves through their inner structure.

238

such as the X ray refraction method and the X They can he applied to both drilled and undrilled pearls. In cultured pearls, they detect the thickness of the "natural" pearl

Radiography methods with

X

rays,

ray silhouette procedure, are effective.

layer

around the foreign body.

Imitations

A

fine imitation

enamel coated with

is

the so-called fish-scale pearl.

essence d'orient,

which

is

produced from the

It

consists of glass or

scales of certain fish. In

other imitations, part of a sea snail (antilles pearls), mussels (takara pearls from Japan), or teeth (of the sea

cow — dugong

pearl) are used. There are also plastic products

on

the market.

The Australian

Japanese pearl in the trade) is included among not a cultured pearl in the trade sense. It consists only of a thin mother-of-pearl layer and some other artificial part. A clay or resin head is fixed to the inner part of a shell and is then covered with a thin pearl layer. After the harvest the bead is removed and replaced by a mother-of-pearl half-bead. The product is begun in Australia, but it is finished into a doublette in Japan. blister pearl (called

the imitations, because this

Operculum

is

The operculum

(Chinese cat's-eye) has a structure similar to a halfbut is actually the slightly arched lid of a sea snail found in the Australasian islands area, where it is used for adornment. It is not well known in Europe. pearl, with a porcelain-type coloring,

Mother-of-Pearl [page 231, nos. 1,11]

The

inner nacreous layer of a mollusk, or sometimes of a snail shell which has an

iridescent play of color,

is

called mother-of-pearl

("mother of the

pearl").

Mother-of-Pearl of the Pearl Mussel The mother-of-pearl of the pearl mussel is most often used. Accordingly, the main suppliers are the pearl farms. The basic color is usually white; it is naturally dark in the mother-of-pearl from Tahiti. For structure, formation, and distribution see the discussion of pearls starting on page 230. Mother-of-pearl is favorably used for ornamental purposes, for clock faces, buttons, costume jewelry, and for inlaid work (such as the handles of knives and pistols).

Mother-of-Pearl of the Paua Mussel The mother-of-pearl of the Paua mussel from New Zealand (Haliotis australis), which has a blue-green iridescent color play, has been used by the indigenous Maori people for centuries for inlays in mystical carvings.

The mother-of-pearl of this mussel has now been used for some time in the Western world, especially for costume jewelry. It is called sea opal, because of similar color effects to those

found in opal.

Mother-of-pearl of the Paua mussel with color play similar to opal.

239

New on

the Market

By highlighting gemstones described

as

being "new on the market,"

necessarily mean that these stones were found only recently.

it

does not

The particular mineral or

aggregate may very well have been known for a long time, but its importance for the gemstone trade has remained minor or insignificant due to its extreme rarity of occurrence in gemstone quality or because it has been poorly marketed. 1

Verdite

cabochons] Light to dark green, often spotty serpentine rock. green color. Mohs' hardness about 3, density 2.8-3.0. Translucent to opaque. Used for sculptures; increasingly also for costume jewelry. Has been

Named

[2

for

its

used for cultural purposes for

a

long time in southern Africa.

Lilac-colored to violet. Through admixture of accombecomes white- or black-spotted or flamed. Translucent to opaque. Mohs' hardness 5-6. Density 2.54-2.78. Monoclinic, K(Ca,Na) 2 [(OH,F) Si 4 O 10 H 2 0. Vitreous to silky luster. Named after river in

2 Charoite [3 cabochons]

panying minerals,

it

•

]

|

Siberia, Russia.

Was

recognized in 1978 as independent mineral.

Opaque metamorphic rock with structure Main parts of the aggregate are feldspars and

3 Gneiss

that produces a decorative

Compact and hard. Density 2.65-3.05. Besides gray and greenish, also brownish and reddish. Used for costume jewelry and ornamental objects. effect.

Opaque

quartz.

main parts of aggregate being quartz and Very compact and hard. Density 2.85-3.20. Named after place of discover}' in South Carolina, United States. En cabochon and barrel-shaped for costume jewelry and ornamental objects.

4 Unakite

granitic rock with

feldspar as well as greenish epidote.

5

Nuummite

[2

cabochons]

Opaque rockof an almost black basic color with main

parts of aggregate being gedrite and anthophyllite; other parts are pyrite, tite,

and chalcopyrite. Because of

a lamellar, fibrous structure, there is

cent play of colors. Mohs' hardness 5'/:-6. Density around

discovery in Greenland. 6

Ammolite

It is

worked

flat

3.

magne-

an

irides-

Named after place of

or en cabochon.

Fossilized shell of ammonites (thereform of aragonite. Because of a lamellar structure of the glass-like shell, there is an opalescent play of colors. Mohs' hardness 4. Density 2.75-2.80. Place of discovery in Alberta, Canada; on the market since 1969. Because it is not very thick, it is often worked into doublets or triplets. fore

name)

(Also called korite)

[3 flat cuts]

in the

7 Carletonite [3 faceted stones]

hardness

4-4 /:. Density 1

Deep

blue, also pale blue. Transparent.

Mohs'

2.45. Tetragonal. Vitreous luster.

8 Katapleite [3 faceted stones] Colorless. Transparent. Mohs' hardness 5-6. Density 2.72. Hexagonal, Na 2 Zr(Si 3 9 ) 2H 2 0. Vitreous luster. 9 Sugilite [2 cabochons] Violet. Translucent to opaque. Mohs' hardness 6-6 /:. Density 2.76-2.80. Hexagonal, Na 3 KLi 2 (Fe,Mn,Al) 2 [Si 12 30 ]. Resinous luster. Formerly erroneously offered as Sogdianite. 1

O

10 Gaspeite 3.7. 11

Sugilite

The

240

[2

cabochons]

Light green. Opaque. Mohs' hardness 454—5. Density

Trigonal, (Ni,Mg,Fe)[C0 3 ]. Vitreous [2

faceted stones]

Violet. (For

luster.

more information

illustrations are 10 percent larger than the originals.

see no. 9 above.)

V*

+

v

,

*

!

.

11

Gemstones

Imitation There

is nothing against the law in producing imitations of gemstones, as long as no harmed or defrauded by it. Imitated stones are indeed an important element of the gemstone trade. Those who do not want the security risk of, or cannot afford, genuine gemstones can use these for their adornment. But when imitations are passed off as more valuable true gemstones at inflated prices, then that is fraud. Imitations must always be designated as such; they have to be named correctly. In the category of imitations we distinguish the imitations which look similar to the gems, the combined

one

is

and

stones,

artificially

made gemstones — the

syntheses.

Imitations Ancient Egyptians were the first who feigned gemstones with glass and glaze, because genuine were too expensive and/or too rare. In 1758, a Viennese, Joseph Strasser, developed a type of glass which served for a long time as a substitute for diamond. It could be cut and was, in fact, very similar to diamond in appearance, due to its high refractive index. Even though production and sale was prohibited by the Empress Maria Theresa, this diamond imitation, called strass, reached the European trade via Paris. Until 1945, Gablonz and Turnau in Czechoslovakia were important centers for the glass-jewelry industry. Then this tradition was taken over by Neugablonz in the Allgau, Bavaria. For costume jewelry, cheap glass was used. For more valuable gemstone imitations, lead or flint glass with a high refractive index is used. Porcelain, enamel, and resins as well as other plastics also serve as gemstone imitations. Most imitations have only a color similar to that of the gemstone; other properties, such as hardness or

fire,

could not be satisfactorily imitated.

New Imitations A special category of imitation is the particular synthetic stone, which, even though it does not have a counterpart in nature, is very similar to other gemstones

good optical effects. These gemno analogous natural gemstone, are nonetheless counted among true gemstones. They usually serve as a diamond substitute. in

its

physical properties and especially

quality substances, with

To

this

category belong the 1953-developed fabulite (occasionally also called YAG, produced since 1969 in gemstone

diagem), a strontium titanate (SrTi0 3 ), and

A

selection of

gemstone doublets and gemstone

triplets

Garnet

Ruby

Rock

crystal

m\ Colored glue

Ruby by Rock

^^W ^r

crystal

*

Rock

Colored glass^

cr V stal

Rock

S P inel

Dal

\

-A

/

Colored glass

Chalcedony

242

Rock

crystal'

'

Colored glass

cr y stal 1

The synthetically made gemstone YAG a

good diamond

is

imitation.

aluminum garnet (Y 3 A1 5 ]2 ) (see photo above right). Other representatives are galliant (also called GGG), a gadolinium gallium garnet (Gd 3 Ga 5 )0 12 djevalite, a calcium zirconium oxide (Zr0 2 /CaO), and linobate, a lithium niobate (LiNb0 3 ). Zirconia, which became available in 1977 (also called fianite and/or phianite or KSZ), an yttrium zirconium oxide (Zr0 2 /Y 2 is 3 ), considered to be the best diamond imitation overall. The list of the artificially produced products that serve as good diamond substitutes numbers more than a dozen. quality (also called diamonaire), an yttrium

,

Combined Stones A popular type of the gemstone imitations are fabrications, in which one part may be a genuine gem, another part

glass, foil,

or

plastic.

There

are

many

combinations;

sometimes two natural gemstone pieces are made even more beautiful with a colorful glue layer to make a larger stone. Stones with two parts are called doublets; stones with three parts, triplets (see the illustration on page 242). Stones which are carefully constructed are difficult to recognize, especially when the seams are covered by the setting.

Synthetic

Gemstones

The dream

of mankind to produce

artificial stones that are really the same as the was realized at the end of the 19th century. The French chemist A. V. Verneuil succeeded in 1888 in synthesizing rubies at a commercial price. In fact, 50 years earlier the first gemstones had been produced synthetically, but they were

natural gemstones

only of scientific interest. The flame fusion process (see page 244) developed by Verneuil

The method

is still

largely used

powdered raw material (aluminum oxidide with dyeing additives) is melted in a furnace at about 3620 degrees F (2000 degrees C). The molten drops fall on a cradle, where they crystallize and form a pear-shaped "boule" (see page 245). Although this boule does not have any recognizable crystal faces, the inner structure is the same as that of a natural crystal. The boules grow to about 3 in (8 cm) thick and several inches high. The growth time is several hours. Verneuil first produced rubies, followed in 1910 by synthetic sapphires; later on, colorless, yellow, green, and alexandrite-colored corundums were produced. By today.

adding

is

as follows:

substance to the smelting, the cultivation of synthetic star rubies and succeeded in the United States in 1947, following Verneuil's method.

a rutile

star sapphires

243

Gemstone Synthesis

Vibrator

Hydrogen Argillaceous earth

powder Sieve

Following the Flame Fusion Process (after Verneuil) Powdered raw material melts in a oxyhydrogen gas flame and drips onto a cradle, where a boule builds up. By the same degree that the bulb grows upward, the cradle is lowered, so that the upper surface of the boule is always the same distance from the burner nozzle.

and gemstones which have

Picture right: Melting bulbs

synthetic

been cut out of them.

Lowering mechanism

Holding device

Crystal nucleus

Drawn

crystal

Smelting

Gemstone Synthesis Following the Drawing Procedure

Heating wire

Melting pot

Heating wire

— Melting oven

(after

A boule is, so to speak, drawn out of the smelting, after a crystal nucleus has initiated the growth of the boule at the surface of the smelting. Under rotation, the Czochralski)

forming boule is continually drawn upward, while it grows respectively

244

on the underside.

Following the Verneuil process, synthetic spinels have also been produced since Their composition, though, is somewhat different from that of natural spinels. With the addition of heavy metals, very good color tints of other gemstones can be achieved, for instance, those of aquamarine and of tourmaline. Synthetic emeralds of usable gem size have existed only since the 1940s, although experiments had been conducted for over a hundred years. Large synthetic crystals of highest purity can also be cultivated with the drawing procedure that was developed in 1918 by the German chemist I. Czochralski. The cultivation product is drawn out of the smelting, after a crystal nucleus has initiated the growth of the boule (see the illustration on page 244). In 1953-54, a diamond synthesis was successful in both Sweden and the United States. But the production costs were so high that it was not viable for the gem trade. However, for industrial purposes, these syntheses have become indispensable. Since 1948, synthetic rutile — sometimes called titania or diamonite — has been produced. It has a dispersion that is six times higher than that of diamond. Today, there are hardly any gemstones left for which a synthetic imitation has not or could not be produced. But whether each possible synthesis can succeed on the market is more a question of the relationship between cost of production and market value. Over a dozen different synthesis procedures are known. Certainly there are others, because companies generally regard these procedures as proprietary information and so keep their advances and details secret. 1910.

Reconstructed Gemstones The so-called reconstructed or recrystallized stones These are gemstones for which little splinters and/or powder of genuine gemstones is melted, sintered, or pressed to form larger pieces. are counted as synthetics.

Imitations

made

in such a

lapis lazuli, malachite,

way are widespread,

especially for amber, hematite, corals,

and turquoise.

Genuineness Test for Diamond It is

often very difficult to distinguish genuine gemstones from synthetics, imitations,

or some other fabrications.

The

refinement and delicacy of execution of gemstone perfect. Often, a test for genuineness is indicated only after very close examination. A testing device that is easy to handle, and that in many cases results quickly in a reliable answer, does exist for diamonds. The tester (a heat-resistance-tester) uses the different abilities of diamond and stones that are diamond substitutes to conduct heat. A special advantage of the device is that it can also be used for diamonds that are already set. Even the smallest pieces can be tested with its fine metal tip. imitations are

becoming more and more

Heat resistance tester to identify

diamond

imitations.

246

Stones of the Zodiac

Symbolism of Stones

Aries Red jasper/

Because gemstones, due to their rarity and their qualities, have always enjoyed a special standing, many people believe that these stones have mystical

Cornelian

Taurus

powers.

Cornelian/ Rose quartz

At first, the principal use of gemstone was as amulets and talismans. As

Gemini

time passed, humankind sought connections to higher spheres, especially

Citrine/ Tiger's

eye

stones

Cancer Chrysoprase/ Aventurine

As a became

Leo

Virgo Citrine/

Yellow agate Libra

Orange citrine/Smoky quartz

associated with stars,

with constellations of stars, and ultimately with the signs of the zodiac.

Along with

this practice

sociations of Rock crystal/ Golden quartz

gem-

result, certain

the stars.

month

came

the as-

stones, birth

stones, and even stones for the indi-

vidual days of the week.

Gemstones as Amulets and

Tal-

ismans

Probably the oldest use of gemstones is linked to the notion that with the help of rare, precious stones, dangers and harms can be averted

and/or fended

Which

off.

stone

is

strongest as

amu-

or talisman seems to have no fixed consensus but, rather, has varied com-

let

Scorpio Blood -red cornelian

Sagittarius Sapphire/

Chalcedony

Capricorn Onyx/ Quartz Cat's eye

pletely,

depending on the culture and

the period examined.

Commonly

the

gemstones associated with one's religion are said to be especially effective. This religious aspect also seems to parallel the development of ideas of commercial value in the trade.

Stones of the Zodiac

The

first

suggestion of the association of gemstones with the 12 signs of the zodiac

Aquarius Turquoise/

Hawk's eye

Pisces

Amethyst/ Amethyst quartz

is

found in the Bible. In several passages 12 gemstones are mentioned together repeatedly. However, which gemstone should be placed with which sign of the zodiac changed over the course of time. Today, this allocation has lost any original meaning; the associations are largely random, with several gemstones (of different price categories)

recommended

as

being equally

appropriate — the sole purpose of which has been to perk up sales.

247

Stones of the

Month

Stones of the Month So-called month were originally

stones of the

January Garnet/ Rose quartz

derived from the signs of the zodiac by referring to the Gregorian calendar;

they are perceived as stones of luck for

These com-

specific calendar divisions.

stones have

February Amethyst/

Onyx

become

(entirely for

mercial reasons) different gemstones

from those of the signs of the Zodiac; and alternatives are assigned equal significance for each

month

as well.

March Tourmaline/ Blood jasper

April Sapphire/

Diamond/Rock crystal

Stones of the Planets

Again

dif-

ferent gemstones, the so-called stones

of the planets, have acquired attributions to help anyone who seeks a psychic-spiritual relationship to the sun,

moon, and

stars.

For

this

purpose, es-

recommended are, for instance, for Mars rubies or red garnets, for Mercury topaz or yellow sapphire,

pecially

May Emerald/ Chrysoprase

for Jupiter blue sapphire, amethyst, or lapis lazuli.

June

Some

Pearl/

Symbol Stones of Nations

Moonstone

nations have, besides flags and coats-

of-arms, also adopted gemstones as national symbols. cially,

July

Ruby/ Cornelian

Those

stones which are

are, espe-

mined within

their borders. Afghanistan, for instance, has identified itself with lapis lazuli,

Australia with opal,

China with

with turquoise, New Zealand with nephrite, and Tanzania with jade, Iran

August Onyx/ Sardonyx

September Peridot

October Aquamarine/ Opal

November Topaz/ Tiger's

eye

tanzanite.

Healing Stones for Body and Soul Formerly, gemstones were used in healing practices as being allegedly effective remedies, sometimes powdered; or, as a symbol, their presence alone was believed to help. Whatever success this lithotherapy claimed is now largely thought to have resulted not directly from the gemstone, but through the healing power of suggestion and belief, ill

December Zircon/

Turquoise

which had

a positive effect

on

the

person. Failures were dismissed by

claiming that the respective gemstone had, after all, not been a "genuine"

one or that the application had been done incorrectly.

248

Table of Constants

How to

Use the Table

This

has

both the professional and the amateur to designed to be used in conjunction with the standard gemological tests. It is not totally comprehensive, hut it should enable the tester to eliminate some possibilities and perhaps suggest some, if he or sheis faced with one of the more unusual examples. Suppose that you have an unknown yellow gemstone to identify. Using the Table of Constants, this is how you go about identifying it: tabic

been

compiled to

identify individual gemstones.

1

Turn

to pages

It

aid

is

254-255, which cover yellow, orange, and brown

2 Test for specific gravity (pages 23-25); this gives 3

Test the refractive index

you

(pages 31-33); this gives a

a

weight of 3.65.

reading of 1.738.

4 Run down the 1.700-1.799 column and across the 3.50-3.99 meet. This gives you several possibilities. 5

stones.

Test for double refraction (page 34). If there is none, the one of the three members of the garnet group.

line until they

field is

narrowed to

periclase or

6 If feasible (see page 20), make a scratch test using the No. 6 is a garnet.

tester. If this

makes

no mark, the stone

7 Turning to the garnet section in the main text, the tester will observe that the absorption spectra of grossular, pyrope, and hessonite are very different. Using the spectroscope (pages 36-39), you can easily identify the class of garnet from which the

specimen stone comes.

Illustration

Acknowledgements

Photos: Dr. H. Bank, Idar-Oberstein: 56 top right; G. Becker, Idar-Oberstein: 89; E. A. Bunzel, Idar Oberstein: 56 top left and below, 57 top and below left, 60 below, 61 below; Chudoba-Guebelin, Edelsteinkundliches Handbuch, Wilhelm Stolifuss Verlag, Bonn: 39; De Beers Consolidated Mines Ltd, Johannesburg, South Africa: 40, 50, 53, 59, 60 top, 72 left, 73, 75; H. Eisenbeiss, Munich: 34; Dr. E. Geubelin Lucerne: 52 below, 57 below right, 85, 93; K. Hartmann, Sobernheim: all gemstone plates as well as 29, 43, 47, 67; Her Majesty's Stationery Office, London: 9; Jain Cultured Pearls, see Heim/Bergstrasse: 61, 226, 227, 228; E. Pauly, Veitsrudt: 144; J. Petsch Jr., IdarOberstein: 52 top; A. Ruppenthal KG, Idar-Oberstein: 138, 140. Drawings: H. Hoffmann, Munich, all diagrams apart from 17; W. Schumann: Das Grosse Buck der Erde (The Large Book of the Earth), Deutscher Buercherbund, Stuttgart: 17.

Chart: R. Webster: The Gemmologists' Compendium, N.A.G. Press Ltd, London.

249

Gem

+

Color White Refr.

Colorless

+ Gray

1.400-1.499

1.500

1.600-1.699

index

Density

1.00-1.99

Ulexite 2-21/2

Ulexite 2-21/2

Gaylussite 21/2-3

Amber 2-2 1/2 Amber 2-3

Kurnakovite 3 Opal 51/2-61/2

2.00-2.49

Gaylussite 2/2-3

Ulexite 2

Meerschaum 2-2 V2

5-5V* Obsidian 5-5VS

Amber 2-3

Hauynite 51/2-6

Apophyllite 4 /2-5 Hauynite 51/2-6 Leucite 51/2-6

Natrolite

Sodalite 51/2-6

Opal 51/2-6V2

Colemanite

41/2

Howlite 3-3/2 Colemanite 4/2 Hambergite 7/2

1

Petalite

6-6 Vi

Hambergite IV2

2.50-2.99

Calcite 3

Vivianite

3-4

1

1/2-2

Vivianite

1

1/2-2

Pearl 21/2-41/2

Pearls 2/2-41/2

Onyx Marble 3 1/2-4 Obsidian 5-5V*

Calcite 3

Calcite 3

Hauynite 51/2-6 Opal 51/2-6V2

Coral

Coral

Howlite 3-31/2

Howlite 3-31/2

3-4

Coral

Anhydrite 31/2 Aragonite 31/2-4 Dolomite 31/2-4 Augelite 4/2-5

3-4

Anhydrite 3V5 Aragonite 3 1/2-4 Dolomite 3/2-4 Onyx Marble 3/2-4

5- 5 1/2

Beryllonite 51/2-6

Datolite

Leucite 5 1/2-6 Skapolite 51/2-6

Nephrite 6-6/2 Danburite I-IV2 Tourmaline 7-7/2 Precious Beryl 71/2-8 Phenakite 7 />-8

Sanidine 6 Labradorite 6-6/2

Moonstone 6-6/2

1

Rock Crystal 7 Smoky Quartz 7 Precious Beryl

3.00-3.49

Fluorite

4

7V5-8

Magnesite 3/2-41/2 Amblygonite 6

Magnesite 31/2-4/2 Apatite 5

Hemimorphite 5 Datolite

Diopside

5-5 V* 5-6

Enstatite 51/2

Amblygonite 6 Nephrite 6-6/2 Jadeite 6V2-I Danburite 7-7/2 Tourmaline 7-7/2 Dumortierite 7-8'/2 Euclase 7/2

3-3/2 Hemimorphite 5

3.50-3.99

Celestine

Willemite 5/2

Topaz 8

4.00-4.99

Witherite

3-3 V2

3-3/2 3-3/2 Witherite 3-3/2 Barite

Celestine

Willemite 5/2

The numbers following the gemstone names

250

refer to

Mohs' hardness

Gem Refr

1.700-1.799

Color White

1.800

1899

+

+ Gray

Colorless 1

900 and higher

index

Density

1.00-1.99

2.00-2.49 2.50-2.99 3.00-3.49

Magnesite

3'/2-4'/?

Diopside 5-6 Clmozoisite 6-7

3.50-3.99

Kyanite

4-7

Benitoite

Periclase 5'/2-6

Benitoite

6-6V2

Zircon 6V2-7'/2

6-6 /?

Sapphire 9

1

Diamond 10

Grossular 6V2-7V2 Sapphire 9

4.00-4.99

Sphalerite 31/2-4

Anastase 5 /2-6 Zircon 6V2-7'/2

1

Zircon 6Vi-7V6

Sphalerite 3 V2-4

YAG8

Linobate 5V2 Zircon 6 /2-7 1

5.00-5.99

Scheelite

1

/2

4V2-5

Hematite 5Vi-6V* Fabulite 6-61/2 Djevalite

8-8V2

Zirconia 8V2

6.00-6.99

Cerussite

3-3 Vi

Cerussite

2-3 3-3 Vi

Scheelite

416-5

Phosgenite

Cassiterite

6-7

7.00 and

Cassiterite

6-7

higher

Galliant 6V2

251

Gem

Color Red Refr index

+

Pink

+ Orange

1.400-1.499

1.500-1.599

Kurnakovite 3 Opal 5V2-6i/2

Amber 2 -2 1/2

1.600-1.699

Density

1.00-1.99

2.00-2.49

Natrolite

5-5 1/2 5-6

Kurnakovite 3 Opal 51/2-61/2 Stichite

\Vi-2Vi

Cancrinite

Gypsum

Opal 51/2-61/2

Meerschaum 2-2 1/2

Tugtupite 51/2-6

2

Apophyllite 4'/2-5

Thomsonite 5-51/2 Cancrinite 5-6 Tugtupite 51/2-6

Opal 51/2-61/2 Petal ite

2.50-2.99

Calcite 3

Coral

3-4

Cancrinite 5-6 Tugtupite 51/2-6 Opal 5 1/2-6 1/2

6-6 ^

Pearl 21/2-4 1/2

Pearl 21/2-41/2

Calcite 3

Calcite 3

Coral

3-4

Coral

Anhydrite 31/2 Aragonite 31/2-4 Dolomite 3'/2-4 Apophyllite 41/2 Cancrinite

3-4

Anhydrite 31/2 Aragonite 3 1/2-4 Dolomite 31/2-4 Nephrite 6-6 1/2 Danburite I-IV2 Tourmaline 7-7V2

5-6

Skapolite 5 />-6 Tugtupite 51/2-6 1

Opal 51/2-61/2 Aventurine Feldspar

Precious Beryl 71/2-8 Phenakite 7'/2-8

6-6V2 Fossilized

Wood

6 />-7 1

Jasper 6'/2-7

Amethyst 7 Rose Quartz 7 Precious Beryl 71/2-8

3.00-3.49

Fluorite

Rhodochrosite 4

4

Apatite 5 Nephrite 6-6 1/2 Kunzite 6V2-7 Jadeite

6^2-7

Danburite 7-7/2 Tourmaline 7—71/2 Dumortierite 7-8V2 Andalusite 71/2 Topaz 8 Rhodizite 8-81/2

3.50-3.99

Celestine

3-3 1/2

Siderite 31/2-41/2

Rhodochrosite 4 Willemite

51/2

Topaz 8

4.00-4.99

Barite

3-3 1/2 3-3 1/2

Celestine

Smithsonite 5 Willemite SVi

5.00-5.99 The numbers following the gemstone names

252

refer to

Mohs' hardness

5

Gem Refr

Color Red

+

Pink

+ Orange

1.700-1.799

1.800-1.899

1.900 and higher

Rhodochrosite 4 Rhodonite 51/2-6V2

Rhodochrosite 4

Purpurite 4-4'/?

Purpurite

index

Density

1.00

1.99

2.00 2.49

2.50-2.99 3.00-3.49

Clinozoisite

3.50-399

4-4 V2

6-6

Sidente 3 />-4 '/>

Sidente 3'/2-4

Rhodochrosite 4

Rhodochrosite 4

Titanite 5-5'/?

Willemite

Titanite 5-5'/?

Anastase 5'/2-6

6-6V2 Almandine 6V2-IV2

Zircon 61/2-7

1

51/2

Rhodonite 51/2-6

1

/2

Benitoite

6-6V2 Almandine 6V2-7V2 Hessonite 6V2-7V2 Benitoite

Zircon 6 /2-7 1

Sphalerite 3'/2-4

Diamond 10

1

/2

Pyrope 6'/2-7i/2 Rhodolite 6 1/2-71/2 Spinel

8

Taafeite

8-8 V2

Alexandrite 8 /2 Chrysoberyl 8V2 1

Ruby 9 Sapphire 9 4.00-4.99

Smithsonite 5 Willemite 5Vi Almandine 6 /2-7 /2 Spessartine 6 /2-7 /2 Gahnite 71/2-8 Painite 71/2-8 1

1

1

1

3V2-4

Smithsonite 5

Sphalerite

Almandine 6V2-71/2 Spessartine 6V2-IV2

Rutile 6-61/2

Zircon 6 1/2-7 1/2

Zircon 6V2-71/2

Gahnite 7V2-8 Painite 71/2-8

Ruby 9 Sapphire 9

5.00-5.99

Proustite 21/2

Krokoite 2 /?-3 Cuprite 3V2-4 1

Zinkite

4-5

Scheelite 41/2Hematite 51/2-6 Tantalite

6.00-6.99

1

/?

6-6V2

Krokoite 21/2-3 Wulfenite 3 Cuprite 3 /2-4 1

Scheelite 41/2-5 Tantalite

6-6 '/?

7.00 and

Wulfenite 3

higher

Tantalite

6-6 1/2

253

Gem

+ Orange + Brown

Color Yellow Refr.

1.400-1.499

1.500-1.599

1.600-1.699

Gaylussite 2/2-3 Opal 5 1/2-61/2

Amber 2-2 1/2 Ivory 2-3

Gagate 2 1/2-4

5-5 1/2

Meerschaum 2-2V5

Hambergite

Obsidian 5-5V5 Moldavite 51/2

Serpentine 2V&-5V5 Apophyllite 41/2-5

index

Density

1.00-1.99

2.00-2.49

Natrolite

71/2

Leucite 51/2-6 Petalite

6-6 1/2

Hambergite

2.50-2.99

71/2

Calcite 3

Pearl 21/2-41/2

Pearl 21/2-41/2

Onyx Marble 3 1/2-4 Obsidian 5-5V2

Serpentine 2/2-51/2 Calcite 3 Aragonite 3/2-4 Obsidian 5-5V5 Beryllonite 51/2-6

Calcite 3

Aragonite 3/2-4 Dolomite 3/2-4 Onyx Marble 3V2-4

Scapolite 51/2-6

Brazilianite 51/2

Sanidine 6 Aventurine Feldspar

Nephrite 6-6 1/2 Prehnite 6-61/2 Danburite I-IV2 Tourmaline 7-7 1/2 Precious Beryl 71/2-8 Phenakite 71/2-8

Opal 51/2-61/2

6-6 1/2 Moonstone 6-61/2 Orthoclase 6-61/2 Tiger's Eye

6/2-7

Datolite

5- 5 1/2

Aventurine 7 Citrine 7

Smoky Quartz Cordierite

7

I-IV2

Precious Beryl 71/2-8

3.00-3.49

Fluorite

4

Ekanite 41/2-6V2

Rhodochrosite 4

Amblygonite 6

Apatite 5 Diopside 5-6

Hyperstene 5-6 Enstatite 51/2 Actinolite 51/2-6

Amblygonite 6 Nephrite 6-6/2 Axinite 6/2-7 Hiddenite 6/2-7 Jadeite 6V2-7 Kornerupine 6/2-7 Peridot 6V2-7 Sinhalite 6V2-7 Danburite 7-7V2 Tourmaline 7-7/2 Dumortierite 7-8/2 Andalusite

71/2

Topaz 8

3.50-3.99

Siderite 31/2-41/2

Rhodochrosite 4 Willemite

51/2

Topaz 8

4.00-4.99

Witherite 3-31/2

Barite

3-3 1/2 3-3 1/2

Witherite

The numbers following the gemstone names

254

refer to

Mohs' hardness

Gem Refr

1.700-1.799

Color Yellow

1.800

1.899

+ Orange + Brown 1

900 and higher

index

Density

1.00-1.99 2.00

Sulphur 1'/2-2

2.49

l

/2

2.50-2.99 3.00-3.49

Rhodochrosite 4

Rhodochrosite 4 Hypersthene 5-6 Epidote 6-7

Purpurite

Purpurite

4-4 /? 1

4-4 Vi

6-7

Clinozoisite

6Vi-7 Peridot 6V2-7 Sinhalite 6Vi-7

Axinite

Vesuvian 6Vi

3.50-3.99

3/2-4 5-5V5

3Vi-4Vi

Siderite 3 /2-4'/2

Sphalerite

Rhodochrosite 4

Rhodochrosite 4

Titanite

Siderite

Kyanite

1

4-7

Titanite

5-5Vi

Hypersthene 5-6

Andradite 6Vi-7 Vi

Willemite 5Vi

Zircon 6Vi-7Vi

5Vi-6

Periclase

Epidote Sinhalite

Anastase 5 /2-6 Andradite 6 /2-7'/2 Zircon 6V2-IV2 Diamond 10 1

1

6-7 6Vi-7

Grossular 6Vi-7 /2 Hessonite 6 /2-7 /2 1

1

1

Pyrope 6Vi-7V2 Staurolite

Spinel

7-7V2

8

Chrysoberyl 8 Sapphire 9

4.00-4.99

1

/2

Willemite 51/2 Spessartine 6 /2-7 Sapphire 9 1

Andradite 6V2-71/2 1

/2

Sphalerite 31/2-4

6-6 Vi

Spessartine 6/2-7 Vi

Rutile

Zircon 6Vi-7Vi

Zircon 6V2-7V2

5.00-5.99

Crokoite2V2-3 Zinkite

4-5

Scheelite 41/2-5

Hematite 5V2-6V2 Tantalite

6-6 Vi

Zirconia 8Vi

6.00-6.99

Cerussite

3-3/2

Crokoite2 /2-3 Phosphogenite 2-3 1

Wulfenite 3 Cerussite

3-3 Vi

Scheelite 41/2-5 Tantalite

6-6 Vi 6-7

Cassiterite

7.00 and

Wulfenite 3

higher

Tantalite

6-6 Vi 6-7

Cassiterite

255

Gem

Color Green Refr.

+ Yellow-green + Blue-green

1.400-1.499

1.500-1.599

1.600-1.699

1.00-1.99

Opal 5 1/2-6 1/2

Amber 2-2/2

Turquoise

5-6

2.00-2.49

Chrysocolla 2-3 Obsidian 5-5/> Moldavite 51/2 Hauynite 51/2-6 Opal 51/2-6/2

Chrysocolla 2-3 Serpentine 2/2-5/2

Turquoise

5-6

Density

Variscite

4-5

Apophyllite 4/2-5 Obsidian 5-5/2

Thomsonite 5-5/2 Moldavite 5/2 Hauynite 5/2-6

2.50-2.99

Onyx Marble 3/2-4 Obsidian 5-5/2 Hauynite 51/2-6 Opal 5/2-6/2

3.00-3.49

Fluorite

4

1 Vi—2 2/2-4/2 Serpentine 2/2-5/2

1 Vi-2 2/2-4/2 Onyx Marble 3/2-4 Datolite 5-5/2

Vivianite

Vivianite

Pearl

Pearl

Variscite

4-5

5-6 5-6

Apophyllite 4/2-5

Tremolite

Wardite 5 Obsidian 5-5/2

Turquoise

Amazonite 6-6/2 Chrysoprase 6/2-7

Nephrite 6-6/2 Prehnite 6-6/2

Aventurine 7 Prasiolite 7

Tourmaline 7-7/2

Aquamarine 7/2-8 Precious Beryl 7/2-8 Emerald 7/2-8

Emerald 7/2-8

Ekanite 4/2-6/2

Malachite 3/2-4 Apatite 5 Dioptase 5

Brazilianite 5/2

Precious Beryl

7/2-8

Hemimorphite 5 Datolite 5-5/2 Diopside

5-6

Hypersthene 5-6 Tremolite

5-6

Enstatite 5/2

Smaragdite 5/2 Aktinolite

5/2-6

Nephrite 6-6/2 Hiddenite 6/2-7 Jadeite

6/2-7

Kornerupine 6/2-7

6/2-7 6/2-7 Tourmaline 7-7/2 Peridot

Sinhalite

Andalusite 7/2 Euclase 7/2

3.50-3.99

Celestine

3-3/2

Malachite 3/2-4

Hemimorphite 5 Hypersthene 5-6 Willemite 5/2

Topaz 8

4.00-4.99

Barite

3-3/2

Smithsonite 5

The numbers following the gemstone names refer to Mohs' hardness

256

Gem Refr

Color Green

1.799

1.700

+ Yellow-green + Blue-green 1899

1.800

1

.900 and higher

Density

1.00

1.99

Sulphur 116-216

2.00 2.49

2.50-2.99 3.00-3.49

Malachite 316-4 Uvarovite 616-716

Malachite 316-4 Dioptase 5 Diopside 5-6

Malachite 316-4

Hypersthene 5-6

6-7 6-7

Epidote

Clinozoisite

Vesuvianite 6V2 Peridot

616-7 6V6-7

Sinhalite

3.50-3.99

Malachite 3 16-4 Kyanite 4-7

Malachite 316-4

Malachite 3 V2-A

5-516 Demantoid 6 6-7 /2 Uvarovite 6V2-7V2 Zircon 6V2-IV2 Titanite

Hypersthene 5-6 Willemite 516 Penclase 516-6 Epidote 6-7

1

1

316-4 5-516 Zircon 616-716 Diamond 10 Sphalerite

Titanite

Sinhalite 6 /2-7 1

Grossular 6 /2-7 1

Spinel

1

/2

8

Taaffeite

8-816

Alexandrite 8 /2 Chrysoberyl 8V2 Sapphire 9 1

4.00-4.99

Malachite 316-4 Smithsonite 5 Willemite 51/2

Gahnite 716-8 Sapphire 9

Malachite 316-4 Smithsonite 5 Zircon

616-7^

Gahnite 7

Malachite 316-4 Sphalerite

3^-4

Zircon 616-716

6-8

1

5.00-5.99

Zirconia 816

6.00-6.99

Phosgenite

2-3

7.00 and higher

257

Gem

Color Blue Refr.

+ Blue-green +

Blue-red

1.400-1.499

1.500-1.599

1.00-1.99

Opal 51/2-6V2

Amber 2-2 1/2

2.00-2.49

Chrysocolla 2-4 Hauynite 51/2-6 Sodalite 51/2-6

1.600-1.699

index

Density

Opal 51/2-6/2

Opal 5 1/2-6 1/2

Gypsum

5-6

Turquoise

2

2-4 4-5

Chrysocolla Variscite

Apophyllite 4'/>-5 Hauynite 5'/2-6

Opal 51/2-61/2

2.50-2.99

Lapis lazuli 5-6 Hauynite 51/2-6

Opal 51/2-61/2

Vivianite

1

V2-2

Pearl 21/2-41/2

Coral

3-4

Anhydrite Variscite

31/2

4-5

Apophyllite 4/2-5

Vivianite

1

Vz-2

Pearl 21/2-4/2

Anhydrite 31/2 Turquoise 5-6 Nephrite 6-6/2 Tourmaline 7-7/2

Wardite 5

5-6

Lapis lazuli

Hauynite 5/2-6 Opal 51/2-6

Amazonite 6-6/2 Chalcedony 6/2-7 Chrysoprase 6/2-7 Jasper 6V2-7 Aventurine 7 Prasiolite 7

Cordierite

1-1 ^h

Aquamarine 71/2-8 Emerald 7/2-8 3.00-3.49

Fluorite

4

Lapis lazuli

Lapis lazuli

5-6

5-6

Apatite 5 Dioptase 5

Hemimorphite 5 Lazulite

5-6

Nephrite 6-6/2 Clinozoisite 6-71/2 Sillimanite

6-7/2

Smaragdite 6/2

6V2-7 6V2-I Tanzanite 6/2-7 Tourmaline 7-7/2 Dumortierite 7-8/2 Axinite

Jadeite

Euclase 7/2

Topaz 8

3.50-3.99

Celestine

3-3 Vi

Hemimorphite Topaz 8

4.00-4.99

Barite

3-3 1/2

Celestine

3-3/2

Smithsonite 5

The numbers following the gemstone names

258

refer to

Mohs' hardness

5

Gem Refr

1.700

1.799

Color Blue 1.800

+ Blue-green +

1.899

1

Blue-red

.900 and higher

index

Density

1.00-1.99

2.00-2.49

2.50-2.99 3.00-3.49

Dioptase 5 Vesuvianite 6/2 Axinite

Purpurite

4-4 Vi

Purpurite

4-4/2

6/2-7

Tanzanite 6/2-7

3.50-3.99

Azurite 3'/2-4 Kyanite 41/2-7 Benitoite Spinel

6-6/2

Azurite 3/2-4 Benitoite 6-6/2 Zircon 6 V2- 7 V2

Zircon 6V2-7V2

Smithsonite 5

Zircon 6VS-7V5

Anastase 5 /2-6 1

Diamond 10

8

Taaffeite

8-8/2

Ruby 9 Sapphire 9

4.00-4.99

Smithsonite 5 Gahnite 71/2-8

Zircon 6V2-7V2

Ruby 9

Gahnite 7Vz-8

Sapphire 9

5.00-5.99

259

Gem

Color Violet Refr.

+ Brown-red

1.400-1.499

1.500-1.599

Opal 51/2-61/2

Amber 2-2 1/2

1.600-1.699

index

Density

1.00-1.99

Opal 51/2-6V2

2.00-2.49

Tugtupite 51/2-6

Stichtite

Opal 51/2-61/2

Tugtupite 51/2-6

V/i-lVi

Opal 51/2-61/2

2.50-2.99

Calcite 3

Coral

Calcite 3

3-4

Coral

Lapis lazuli 5-6 Tugtupite 51/2-6

Opal 51/2-61/2

Calcite 3

3-4

Coral

Anhydrite Charoite 5-6

31/2

5-6

Lapis lazuli

Ska polite 51/2-6

3-4

Anhydrite 31/2 Nephrite 6-61/2 Sugilite

6-6 1/2 7-7 1/2

Tourmaline

Tugtupite 51/2-6

Opal 51/2-61/2

Wood 6V2-7

Fossilized

Jasper 6/2-7

Amethyst 7 Amethyst Quartz 7 Rose Quartz 7 Cordierite

3.00-3.49

Fluorite

4

Lapis lazuli

7-7 1/2

Lapis lazuli

5-6

5-6

Amblygonite 6

Apatite 5

Amblygonite 6 Nephrite 6-61/2

6/2-7 6V2-7 Kunzite 6/2-7 Tanzanite 6/2-7 Dumortierite 7-8/2 Tourmaline 7-7/2 Axinite

Jadeite

Topaz 8

3.50-3.99

Topaz 8

4.00-4.99

Smithsonite 5

5.00-5.99

6.00-6.99 7.00 and higher

The numbers following the gemstone names

260

refer to

Mohs' hardness

Gem Refr

1.700 -1.799

Color Violet

+

Blue-red

1800 1899

1

Purpurite 4-4'/?

Purpurite 4-41/2

Benitoite 6-6^2 Almandine 6V2-7V2 Zircon &Vi-7Vi

Zircon 6V2-7V2

Zircon 6 /2-7'/2

900 and higher

index

Density

1.00-1.99

2.00-2.49

2.50-2.99

3.00-3.49

Axinite

6V2-I

Tanzanite 6V2-7

3.50-3.99

Benitoite 6-6V2 Almandine 6V2-IV2 Spinel 8 Taaffeite

8-8 V*

Ruby 9 Sapphire 9

4.00-4.99

5.00-5.99

Smithsonite 5

Smithsonite 5

Almandine 6V2-IV2

Almandine 6 /2-7

Gahnite 71/2-8 Ruby 9 Sapphire 9

Zircon

1

1

1

/2

6V2-W2

Gahnite 7 />-8 1

Proustite2 /2 Cuprite 31/2-4 1

Tantalite

6-6V2

Zirconia 8V2

6.00-6.99

7.00 and

Cuprite 3'/2-4 Tantalite

6-6 Vi

Tantalite

6-6 Vi

higher

261

Gem

Color Black Refr.

+ Gray

1.400-1.499

1.500-1.599

1.600-1.699

Opal 51/2-61/2

Amber 2-2 1/2 Coral 3-4

Gagate 21/2-4

index

Density

1.00-1.99

Opal 51/2-61/2

2.00-2.49

Obsidian 5-5/2

Meerschaum 2-2 1/2

Sodalite 51/2-6

Obsidian 5-5/2 Opal 51/2-61/2

Opal 51/2-61/2

Hambergite

2.50-2.99

Obsidian 5-5V2 Opal 51/2-61/2

Hambergite

71/2

71/2

Pearl 2 1/2-41/2

Pearl 21/2-41/2

Aragonite 3/2-4 Obsidian 5-5V2 Opal 5 1/2-6 1/2

Aragonite 3V2-4 Nephrite 6-6/2 Tourmaline 1-lVi

Sanidine 6 Labradorite

6-6 1/2

Chalcedony 6V2-7 Fossilized Wood 6/2-7 Jasper 6 1/2-7 Smoky Quartz 7

3.00-3.49

Fluorite

Hypersthene 5-6

4

Nephrite

6-6 1/2

6V2-7 Tourmaline 7-7/2 Jadeite

Hypersthene 5-6

3.50-3.99

4.00-4.99 5.00-5.99

6.00-6.99 7.00 and higher

The numbers following the gemstone names

262

refer to

Mohs' hardness

Gem Refr

1.700-1.799

1.800

Color Black

+ Gray

1.900 and higher

1.899

index

Density

1.00-1.99

2.00-2.49

2.50-2.99 3.00-3.49

Hypersthene 5-6 Epidote

3.50-3.99

6-7

Hypersthene 5-6 Epidote

Andradite6 /2-7'/2 1

6-7

1

Staurolite 7-7'/2

Spinel

Anastase 5V2-6 Andradite 6 /2-7 Diamond 10

1

/2

8

Sapphire 9

4.00-4.99

Gahnite 71/2-8 Sapphire 9

Andradite 6 /2-7 Gahnite 7 />-8 1

1

1

/2

Chromite 5 /2 Rutile 6-616 1

Andradite 6 /2-7 1

5.00-5.99

6.00-6.99

l

/2

Hematite 5V5-6VS Cerussite

3-3 Vi

Cerussite

3-3 V2

7.00 and higher

263

Gem

Color Multicolored Ref

+

Iridescent

1.400-1.499

1.500-1.599

1.00-1.99

Opal 5 1/2-61/2

Opal 5/2-6/2

2.00-2.49

Opal

Serpentine 2/2-5/2 Howlite 3-3/2 Tugtupite 5/2-6 Opal 51/2-6/2

Howlite 3-3/2 Turquoise 5-6 Turquoise 5-6

Serpentine 2/2-5/2 Howlite 3-3/2

Howlite 3-3/2 Onyx Marble 3/2-4 Tufa 3/2-4 Ammolite 4 Turquoise 5-6 Nephrite 6-6/2 Tourmaline 7-7/2

r.

1.600-1.699

Density

51/2-61/2

Tugtupite 51/2-6

2.50-2.99

Onyx Marble 3 1/2-4 Lapis lazuli 5-6 Tugtupite 5/2-6 Opal 51/2-6/2

Onyx Marble 3/2-4 3/2-4 Ammolite 4 Charoite 5-6 Lapis lazuli 5-6 Tugtupite 5/2-6 Tufa

Opal 5/2-6/2 Jade-Albite 6

Aventurine 6-6/2 Labradorite 6-6/2

Moonstone 6-6/2 Peristerite 6-6/2 Agate 6/2-7 Chalcedony 6/2-7 Fossilized Wood 6/2-7 Jasper 6/2-7 Moss Agate 6/2-7 Amethyst Quartz 7 Aventurine 7 Tiger's Eye 7

3.00-3.49

Fluorite

4

Lapiz lazuli

Lapis lazuli

5-6

5-6

Malachite 3/2-4 Rhodochrosite 4 Nephrite 6-6/2 Jadeite

6/2-7

Tourmaline 7-7/2

3.50-3.99

Malachite 3/2-4 Rhodochrosite 4

4.00-4.99

Malachite 3/2-4

5.00-5.99

6.00-6.99 7.00 and higher

The numbers following the gemstone names

264

refer to

Mohs' hardness

Gem Refr

1.700

1.799

Color Multicolored + Iridescent

1.800

1.899

1

900 and higher

index

Density

100

1.99

2.00-2.49

2.50-2.99 3.00-3.49

Malachite 3 />-4 Rhodochrosite 4 1

Malachite 3 Vi -4 Rhodochrosite 4

Malachite 3'/2-4

Malachite 3'/2-4 Rhodochrosite 4

Malachite 3 />-4

Rhodonite 5V2-6

3.50-3.99

Malachite 3'/2-4 Rhodochrosite 4

1

Rhodointe 5V4-6VS Alexandrite 8V2

5.00-5.99

6.00-6.99 7.00 and higher

265

Bibliography Anderson, B. W., 1971:

Gem

Testing.

London.

Betechtin, A. G., 1971: Lehrbuch der speziellen Mineralogie. Leipzig, East Germany. Bruton, E., 1977: Diamonds. 2nd Edition, Northwood, London.

Chudoba, K. E & E. J., 1974: Edelsteinkundliches Handbuch. Bonn, West Germany. CIBJO, 1975: Bestimmungen zur Benennung und Beschreibung von Edelsteinen, Perlen, Kulturperlen, Synthesen, Imitationen. Bern, Switzerland.

Copeland, L. L., 1960: The Diamond Dictionary. Los Angeles, U.S. Dake, H. C, 1950: Northwest Gem Trails. Portland, Oregon, U.S. Eppler,

W.

E, 1973: Praktische Gemmologie. Stuttgart,

West Germany.

1966: The Science of Gems. Scribner's Sons, Gubeline, E., 1974: Innenirelt der Edelstein. Dusseldorf, Fisher, P.

J.,

Henry, D.

Gem

New York. West Germany.

Long

Beach, California, U.S. Jahns, R. H., 1975: "Gem Materials" (pp 271-326), Industrial Minerals and Rocks. 4th Edition, A.I.M.E., New York. Kraus, E. H. & C. B. Slawson, 1947: Gems and Gem Materials. McGraw-Hill, New J.,

1952:

Trail Journal.

York Lewis, D., 1977: Practical

Gem

Testing.

Northwood, London.

Lenzen, G. 1966: Produktions-und-Handlegeschicte des Diamanten. Berlin. Lenzen, G., 1973: Kurzgefasste Diamantenkunde. Kirschweiler. Liddicoat, R. T., Jr., 1962: Handbook of Gem Identification. Los Angeles, U.S. Mclver, J. R., 1967: Gems, Minerals, and Rocks in Southern Africa. Elsevier (U.S.),

New

York.

Pagel-Theisen, V, 1972: Diamanten-Fibel. Frankfurt, West Germany. Ramdohr, P. & H. Strunz, 1967: Klockmanns Lehrbuch der Mineralogie. Stuttgart, West

Germany. Schlossmacher, K., 1969: Edelstein und Perlen. Stuttgart, West Germany.

Schumann,

W,

1975: Steine und Mineralien. Munich,

West Germany.

Shaub, B. M., 1975: Treasures from the Eaith. Crown Publishers, New York. Shipley, R. M., 1945: Dictionary of Gems and Gemology. Los Angeles, U.S. Sinkankas, J., 1959: Gemstones of North America. D. Van Nostrand, Princeton., N.J., U.S. Sinkankas, J., 1972: Gemstone and Mineral Data Book. New York. Smith, G. F. H. & F. C. Phillips, 1962: Gemstones. 13th edition, Methuen & Co.,

London. Strunz, H., 1970:

Mineralogische

Tabellen. Leipzig,

East Germany.

Walton, J.: Tabellen zur Edelstein-Bestimmung, 2. Auflage, Stuttgart, West Germany. Webster, R., 1970: The Gemmologist's Compendium. 5th edition, Northwood, London. Webster, R., 1975: Gems in Jewellery. Northwood, London. Webster, R., 1975: Gem Identification. Sterling Publishing Co., New York. Webster, R., 1976: Practical Gemmology. 6th edition, Northwood, London. Journal of the German Gemmological Association, Idar-Oberstein. Gems and Gemology, Gemological Institute of America, Los Angeles, U.S. Gems and Minerals, Mentone, California, U.S. Journal of Gemmology, Gemmological Institute of Great Britain, London. Lapidary Journal, San Diego, California, U.S. Schweizer Strahler, Journal of the Swiss Association of Mineral Collectors and Polishers.

266

Index Page numbers printed

ill

M

bold indicate the main reference. Aventurization 4S

Broolrite

Axinite 182

Buergitc 110

Actinolitc J3, J6,

A/.urc malachite 174, 176

Burma ruby 82

Adaminc

A/.urite 174

Burnite 174

Absorption spectrum Achroitc 110

38,42,204 210

JO, 13,

Adelaide ruby 13 Adularescence 44

Bustamite 33, 214 Button pearl 237

African emerald 13

Baguette 66 Bahia topaz 120

Agalmatolite 222

Balasruby 13,85, 100

Agate 60, 116, 126, 132 Agate jasper 146 Agate opal 152 Agirinaugite 33, 216 Alabaster 222

Alamandine 104 Alaska diamond

13

Albite-jadeite 154

Alexandrite 38, 42, 98 Amatrix 196

Amazonite 164

Amber

50,

228

Amblygonite 192 Ambroid 228 American jade 13

Ruby

13

Amethyst quartz 27, 116, 118 Ametrine 118 Amiant 124 Ammolite 34, 48, 240 Analcime 30, 34, 212 Anatase 36, 212

Ball cutting 62

Calcite 19, 34, 36, 38, 47, 48,

amber 228 Banded jasper 146

Californian ruby 13

Barite33, 36,42,

Basanite 146

Cape chrysolite 13 Cape ruby 13, 85

Bastite

Cannel coal 226 Cape 76

202

Bayldonite 30, 33, 68

Carat

Benitoite 184

Beryl 90

Carbonado 72 Carletonite 240

Beryllonite 190

Cassiterite 184

Binghamite 204 Birmite 228 Biwaco cultured pearl 236 Bixbite 30, 68, 96

Cat's eye

Black coral 224 Black opal 150 Black Prince's ruby

Cat's silver 216

8,

98

Effect 45

Quartz 124 Cat's gold 162

Celestine33, 36,208 Centenary 78 Cerussite 200 Ceylonesian diamond 13

Opal

13

Chalcedony

38, 116,

Chambersite

33,

68

13

Change of color 28

Quartz

122

Chatoyancy 45, 124

116,

Spar 192

Bohemian

Chiastolite 178 chrysolite 13

Ruby

13

Garnet 104 Boleite 30,

Aragonite 34, 36, 47, 208 Argyle mine 73 Arizona ruby 13

Boracite 33, 36, 214 Boulder opal 150

210

Spinel 100

Chromite

Boule 243, 244 Bouteille stone

220

Bowenite 38, 202 Brazilian aquamarine 13

Sapphire 13 Brazilianite 190

Brilliance 41 Brilliant 41, 77, 81

cut 66, 80

Bronzite 192

Childrenite 68 Chile lapis 172

Chloromelanite 154 Chondrodite 68 Chrome chalcedony 126 Diopside 190

13

Aquamarine 94

Ruby

126

Chalcopyrite 206

Moonstone

Apophyllite 34, 36, 206

Quartz 122

26

(ct)

Ceylonite 100

Blue Alexandrite 13 Ground 72 John 198

Diamond

Arkansas diamond 13 Art of stone cutting 59, 142 Aschynite 30, 68 Asparagus stone 194 Asterism 44 Augelite 34, 210 Aventurine 45, 116, 122 Feldspar 45, 166

85

230 Blood jasper 128, 146 Bloodstone 128, 162

Anyolite 84, Apatite 19, 194

Spinel 13

Californite 186

Canasite 68 Cancrinite 34, 36, 216

Blister pearl

239 160

206

Baroque pearl 237 Stone 63 Barrel pearl 237 Barytocalcite 208

Blende 200

Antilles pearl

208

Baltic

Andesine 34, 216 Andradite 106 Angel skin coral 224

Opal 152

Cabochon 66 Cacholong 152

Spinel 100

Andalusite 178

Anglesite30, 33, 36, 210 Anhydrite 34, 206 Anorthite 68 Anthophyllite 30, 68 Antigorite 202

$3,68

13

30, 263 Chrysoberyl 45, 98 Cat's eye 98 Chrysocolla 200 Quartz 200

Chrysolite 158

Chrysoprase 116, 126, 128 Chrysotile 202 Chute 237 CIBJO 12, 76 Cinnabar 30, 33, 214

267

Cinnabarite 214 Cinnamon stone 106 Circular agate 134 Citrine 116, 120 Cleavage 22, 64

Dendritic agate 116, 126, 130,134 Density 22

Clinohumite 33, 68, 212

Diamond

Clinozoisite 33, 36, 184, 212

Coal 77 Cobalt calcite 208 Coeruleite 30, 68 Colemanite 34, 48, 206 Color 27 grading 76

Descloizite 68, 212

Diamonaire 243 14, 19, 20, 38, 57,

64,70

Cut

66

61,

Falcon's eye 116, 124

Fancy diamond 76 Feldspar 36, 164 Ferberite 214 Fergusonite 30, 68 Fianite 243

Finch diamond mine 52

Brilliant 26, 77

Club 74 Cut 80 Exchange 74 Diaspore 33, 214 Dichroism 41

Fire 35

precious stone 10

Dichroite 180

Fish silver pearl 239

stone

Dichroscope 41 Diopside 190 Dioptase 194

Flag 50 Flawless (viewed with loupe) 77 Flint glass 36 Florentine 78 Fluorescence 47

10, 61

Common

opal 152

Conch pearl 233 Conchyn 230 Connemara 202, 218 Coral 224

Opal 152 Firing 28

Fish-eye stone 206

Dispersion 35 Disthene 196 Djevalite 18, 21, 25, 33, 36,

75,243 Dolomite 34,

Cordierite 180

Cornelian

Agate 134

116,

Onyx 142 Corundum 19,

126 36,

82

Creedite 34, 68 Crokoite 33, 208 Crokydolite 124 Cross stone 178 Crystal 11, 76 Opal 150 Crystallography 11 Crystal step 15 lattice 14

Crystal system 15, 17

Fluorite 19, 47, 198 36, 48,

206

Fossil

Double refraction 34 Doublet 242, 243

Fossilized

Dravite 110

Fracture 22

Dresden 78

Fraunhofer's lines

Drum

polishing 63

Freshwater pearl 236

Druse

15

Friedelite 30,

pearl

239

239 Cultured pearl 230, 233, 238 Cuprite 33, 206 Cutting form of 66 grading of 77 type of 66 Cutting colored stones 61 Cutting hardness (resistance) 19,20 Cyanite 196 Cymophane 98 Cyprine 186 Czochralski 246

Danburite 182 Datolite 33, 36,

204

Davidite 216

De Beers De Long

star

Dendrite 130

268

ruby 84

36, 38, 106

wood

126,

148

Fowlerite 168 35

33,210

Fuchsite 216

Quartz 182 Durangite 30, 33, 68 Dutoitspan diamond 78

Gadolinite 30, 33,210

Ebauching 60, 61 Edward ruby 84 Egyptian jasper 146 Eilat stone 176, 200

Galliant 18, 21,25, 33,36,

Gagate 226 Gahnite 33, 36, 38, 100, 204 Gahnospinel 33, 100 75, 243 Garnet 104

Ekanite 34, 36, 38, 210 Elaolite 212

Jade 106 Gasperite 240 Gaylussite 34, 208

Etbaite 110

Gem

Emerald 39, 51, 90 Cut 93 Quartz 122

Gemology 10 Geode 15 German diamond

Emery 82 Emperor jade 154 En cabochon 66 Engraving 59, 142, 144 Enhydrose 134 Enstatite 192

142

Lapis

13, 146,

13

172

GGG 243 GIA76 Girasol 150

Glass 34

Opal 152

Eosphorite 33, 214 Epidote 184 Euclase 178

Glyptic 59, 142 Gnat stone (mosquito agate) 130

Eudialite 34, 68, 212

Gold 208 Golden beryl 42, 96 Gold of the North 228 Gold obsidian 220

Euxenite 30, 68 Excelsior 78 Eye agate 134 Eye diorite 120

74, 78

Demantoide

222

Dumortierite 182

CS0

74 Culet 81 Cullinan 22, 64, 78 1.78 II. 8, 78 IV. 78 Cultured blister pearl 236,

Fortification agate 134

Dop65

Dugon

a

Fabulite 18, 21, 25, 33, 36,

75,243 Facet 80

Gold-river 166 Gold topaz 13, 102 Goshenite 96 Goyazite 68 Grading 65

1

G«in26,237 Gruri 26 rrandidierite 68

Greenoddte

10,

(

irossular 106

(

.iiii.i

14, 16,

19,

210

JO, 33,

Mandarin spessartine 104 Manganese pebble I6K Manganesespar 168

kakortokite 220

Manganotantalite 30, 33,

Kimberley mine 72, 73

210 Maraba amethyst Marble onyx 218

Kimberlite 72

Marcasite 30, 68, 162

King cut

Marmarosch diamond

Katapleite 34,

19

240

keshi pearl 234

[arlequin opal 150

204

leat-resistance tester

246

81

Heavy spar 206

King's topaz 13

Heliodore 42, 96 Heliotrope 116, 126, 128 Hematite 128, 162

Kohinoor 78 Korean jade 13 Korite 240 Kornerupine 186

Hemimorphite 198 Hercynite 100 Herderite 34, 36, 214 Hessonite 33, 36, 38, 106 Hiddenite 114 Highlight cut 81 Hodglansonite 33, 68 Hole board 61

Honey opal Hope 78

152

Kunzite 114 Kurnakovite 34, 206 Kyanite 20, 196

Labradorescence 46 Labradorite 46, 166

Lamproite 72 Landscape (scenic) agate

230 Hornblende 30, 68, 212 Hornstone 146 Howlite 34, 208 Hubnerite30, 68, 214 Hyacinth 108

Lapidary 61 Lapis 172 Lapis lazuli 172 Lattice 14

Lawsonite 33, 69 Layer-stone 142

Hyalophane 68 Hydrogrossular 106

Lazulite 192

Hydrophane 152

Lazure stone 172 Lead horn ore 208 Leaf serpentine 202 Legrandite 33, 216 Leifite 69 Lepidolite 69

Hydrostatic scale 23

Hypersthene

33, 38, 42,

76

Ideal brilliant 81

Idocrase 186 Illam 84, 88 Ilmenite 30

68

242 Imperial jade 154 Imperial State Crown Inclusion 49, 77 Inderite 34, 68 Indesite 30

Indian jade

13,

Indigolite 110

Intaglio 142 Iolite

180

Iridescence 46 Ivory 226

156

204

118

13

Marquise 66 Matara diamond 108 Matrix turquoise 170 Marura diamond 13, 108 Maw-Sit-Sit 156 Maxixe-aquamarine 94 Mazarine cut 80 Meerschaum 222 Melanite 106 Melinophane 30, 34, 216 Melonite 30, 68 Mesolite 30, 34, 216 Mexican diamond 13 Jade

Jasper 146 Marble 218

Hyalite 152

Ilvaite 30,

130,

134

Pearl

IDC

36,212

cut 81

Magnesite H, 214 Magnetite JO, 214 Jade 206 Malachite 176

226 Jonker diamond 78 Jet

[ambergite ISO

Haiiynite 36, I

\9

15

Hardness 1

Magna

2

Jcrcmcjewite

Halite 47 1

Japan pearl

Jasper agate 146 Jellvopal 150

lypsuin stone 222

Habit

Madagascar moonstone 166 Madeira top../ 13, 102, 120

Jardm 90

percha 224, 226

Gypsum (

212

cultivation 2 10

Jadeite *8, 154

fade alhitc 154

Grammatite 216 (

Mabe

Jade 154

13

Onyx 218 Midnight

star

89

Milarite 30, 34, 212 Milk opal 152

Mimetesite 30, 33, 68

Mine

55

Mineral 11 Mineralogy 1 Mineral step 15 Mixed cut 66

Mocca

stone 130

Mohs' hardness Moldavite 220

Momme 26, Momo 224

19

237

Lesser Star of Africa 8 Leucite 34, 36, 204

Monazite

Leucogarnet 106 Leucophane 214 Leucosapphire 86 Leuzite 204

Montebrasite 30, 34, 214 Mookaite 146 Moonstone 44, 164

Liddicoatite 110

Morion

Light refraction 31 Light star 31

Moro 224

Limespar 208 Linarite 30, 68 Linobate

21, 25, 33, 36, 75,

243

30,

68

Montana ruby

13

Morganite 42, 96

Moss

116

agate 116, 126, 130, 134

Opal 152 Mother-of-pearl 230, 239 Mtorodite 126 Multi-colored jasper 146

Lithiophilite 33, 68, 212

Ludlamite 33, 210 Luminescence 47

Nassak 78

Luster 41, 46, 230

Navette 66

Natrolite 34, 36,

204

269

Neolite 170

Neo-turquoise 170 Nepheline 34, 212 Nephrite 156 Neptunite 30, 33,69,212 Niccolo 142 Nonmineral 68

Pink pearl 233 Beryl 96 Pipe 72 Pique 77

Rio Grande topaz 120 River 76 River amber 228 opal 239

Pistazite 184

River pearl 198

Pitt

Placer 54 Plagioclase 164

Obsidian 220 Ocean pearl 232 Odontolite 226 Old cut 80

Plasma 146 Pleochroism 41

Oligoclase 34, 210 Olivine 158

Pollucite 34, 36,

Onyx

126, 142, 218

Opal 29,

56, 150

Rock Rock

78

Rohrbach's liquid 24

Rose quartz

Red

iron stone 162 zinc ore

Opaque 41 Operculum 239

Precious beryl 96 Coral 224 Opal 46, 150

Painite 18, 33, 42, 68, 253

Palygorskite 69

206

Resistance hardness (cutting)

Practical fine cut 81

Prase 42, 116, 122, 146

Padparadscha 86, 88 Pagoda stone 222 Pagodite 222

lead ore

iron ore 162

216

Polyhedric quartz 134 Porcelain opal 152

Agate 152 Matrix 150 Opalescence 46, 150, 152 Opaline 150

Orient 230 Oriental amethyst 13 Hyacinth 13 Pearl 232 Peridot 86 Topaz 13, 86 Orlow 78 Orthoclase 19, 39, 42, 164

166, 122

208 copper ore 206 glass head 162

Pleonaste 100 Polishing 60, 62

19,

20

Rondiste 80, 81 Rounding 65

Opal 152 Precutting 60

120

Prasiolite 116,

10 crystal 116

Rubellite 15, 110

Rubicell 100

Ruby

82

Soap 54

Ruin marble 218 Rumanite 228

Stone 10 Stone hardness 19

Russian jade 156 Rutile33, 36, 49, 204

Topaz 102 Prehnite 188

Salamanca topaz

Pressed amber 228 Princess-144 cut 81 Prismatine 186 Prosopite 68

Sanidine 34, 43, 204 Santa Maria Africana 94

Proustite 33,

Sapphire 39, 86

Quartz 122

208

Sapphirine 33, 216 Sard 116, 126

Pseudoagate 134 Pseudomorphosis 15 Pumpellyite 69 Purity grading, 77

Onyx

142

Stone 134

Sawing 64 Saxon chrysolite

Parisite 30, 33, 214 Parker Brilliant 81 Paua mussel 239 Peace ruby 84

Purpurite 33,42,206 Pyrargyrite 30, 33, 214

Pynte 162

Scheelite 196

Pearl cultivation farm 235

Pyrolusite 30, 216

Schorl 110

Pearls

230

Pebble zinc ore 198 Pectolite 34, 212 Pendeloque 66 Periclase

33,206

Pyrope 104 Pyroxmangite

13

13

69

brilliant 81

Scapolite 188

Quartz cat's

14, 19, 36, 39,

eye 44, 124

116

Scorzalite 68

Scratch hardness 19

Secretion 22

204 Peruzzi cut 80

Radiant 81 Raspberryspar 168

Peristerite

Ray stone 204

Petalite 188

wood

Petrography Petrology 11

Diamond

Scandinavian standard 30, 33,

Peridot 158

Petrified

13

148

11

Realgar 30, 68 Reese turquoise 170 Reeves star ruby 84

Seed pearl 232 Selenite 210 Sellaite 34, 68 Semi-precious stone 10 Senarmontite 33, 214 Sepiolite 222 Serpentine 202

Petschite 188

Refractive index 31

Phenakite 180 Phianite 243 Phosgenite 22, 48, 208 Phosphophyllite 34, 36, 210 Phosphorescence 47 Picotite 100 Picture stone 222 Piemontite 30, 68, 184 Piercing/drilling 63

Refractometer 31 Regent 78 Reindeer stone 204 Reitz 78

Serra topaz 13

Rhodizite33,252 Rhodochrosite 168

Siberian chrysolite 13

Rhodolite 104 Rhodonite 168 Ricolite218

Siberite 110

270

Shell pearl 232 Siamese aquamarine Siam ruby 82

Ruby

13,

85

Siderite33,206 Silex 146

13

S.Ik

46

Sillimanite 16, 19, 4* Silver

208

Obsidian 220 Simctitc 228 Simili

diamond

Simpsonite

13,

Table cut 81 Stone 80 Takara pearl Talc

V;iiisi ice

2

Tantalite

w

210

19, 34,

u, 204

Verdelite 110

Tanzanite 160 Tavmavite 184

13

214

196

Quartz 196 Vayrynenite 68 Vcrd-antiquc 202 Verdite 39, 240

Sinhalite 186

Tektitc 220

Smaragdhe 204 Smelting 230

Television stone 202

Verneuil proceai 243 Vesuvianite 39, 186 Vesuvian jade 186

Thalenitc 69

Vicen/.io Teru/./.i 80

Smithsonitc 19K

Thaumasite

Smoky quartz 49,

116

Snowflakc obsidian 220 Soapstone 210 Socialite 174 Sogdianite 33, 69 Spanish topaz 13 Spectral color 27 Spectrolite 44, 46, 166

Spectroscope 37 Spessartine 104 Sphalerite 200

Sphene 194 Spinel 39, 100 36,

114

Spurrite 33, 69 St. Edward's sapphire 89 Star effect

victoria 78

Thick stone 80

Thomsonite

cut 66

Spodumene

216

Vielling 15

Thin stone 80

Topaz 13

Smooth

34,

44

34, 252,

256

Thorianite 30, 68 Thoulet's liquid 24 Thulite43, 160 Thunder egg 134 Tiffany 78 Tiger's eye 116, 124 Tiger's iron 202 Tilting chair 140 Timur ruby 85 Tin stone 184 Titanite 194

Tolkowsky Brilliant 81 Tooth turquoise 226 Topaz 19, 102 Topazolite 106

Toscan 78 Tourmaline 110 Transparency 41

Quartz 116 Starlite 108

Star of Africa 78

Staurolite 33, 36,43, 212

Transvaal jade 13, 106 Trapiche emerald 92 Tree gold 78 Tremolite 34; 36, 39, 43, 216 Triangle 66

Steatite 210

Trichroism 41

Asia 89 India 89 Sierra

Leone 78

Stellerite

69

Triphyline 33, 212 Triple goods 80

Step 15 Step-cut 66 Stibiotantalite 30, 33, 68 Stichtite 18, 21,25,

34,202

Triplet 15, 242, 243 Trystine 118

Tsavolite 106

Stone of the month 248 Stones of the zodiac 247

Tscharoite 240

Strass 21, 75

Tube

Diamond

agate 134

Stuart sapphire 89 Succinite 228

Twin

Streak 28 Strontianite 34, 36,

214

Structure 15

13,

170

Viridine 178

Vivianite34,43,208 Vlasovite210 18, 34, 68, 256 Water chrysolite 220 Watermelon tourmaline Water sapphire 180 Water stone 134

Wardite

Waxy

112

opal 152

White lead ore 200 White opal 150 Weight 22 Wernerite 188 Wesselton 76 Westphalian balance 24 Whewellite 34, 36, 212 Willemite33, 36, 39, 43,47, 48,

204

Williamsite 48, 202 Wing mussel 232

Witherite 34, 48, 206

Wolframite 30, 214 Wollastonite 69

Wooden

opal 152

Wulfenite 33, 36, 208 Wurtzite 30 Wyoming jade 156

Tsilaisite 110

Tufa 218 Tugtupite 34, 204 Thunder egg 134 Turquoise 112 Matrix 170

13

Viennese turquoise Villaumite 68 Violane 190

15

240 Sulphur 33, 208

YAG18,

21, 25, 33, 36, 75,

243 Yellow ground 72 Yellow lead ore 208 Yttrotantalite 68 Yugawaralite 34, 216 Yiinan jade 156

Sugilite 33,

Sulphur pebble 162 Sunstone 166 Surface luster 44

Suspension method 24 Swiss lapis 146, 172 Synthesis 11, 242,243

Zebra jasper 146 Zektzerite 34, 212 Zinc blende 200

Ulexite 202

Unakite 240 Urals emerald

13

Utahlite 196

Uvite 110 Uvarovite 106

Zincspar 198 Zincspinel 100, 204 Zinkite 33, 206

Zircon 108 Zirconia

Taaffeite 33, 39,

214

Vanadinite 30, 68 Variety 11

18, 21, 25, 33, 36,

39, 75,

243

Zoisite 160

271

BOSTON PUBLIC LIBRARY

g ^

3 9999 03211 978 4

BRIGHTON BRANCH LIBRARY

Library of Congress Cataloging-in-Publication Data

Schumann, Walter, [Edelsteine und Schmucksteine. English] Gemstones of the world / Walter Schumann

— Rev. &

expanded

ed.

cm.

p.

Includes bibliographical references

(p.

-

)

and index.

ISBN 0-8069-9461-4 Precious stones. 1997 553.8 — dc21 1.

I.

Title.

QE392.S54513

97-380

CIP

Translated by Annette Englander

10

9

7

6

5

4

3

2

1

Published 1997 by Sterling Publishing Company, Inc. 387 Park Avenue South, New York, N.Y. 10016 Originally published by BLV Verlagsgesellschaft mbH

under the title Edelsteine und Schmucksteine © 1995 by BLV Verlagsgesellschaft mbH, Munich English translation © 1997 by Sterling Publishing Co., Inc. Distributed in Canada by Sterling Publishing % Canadian Manda Group, One Atlantic Avenue, Suite 105 Toronto, Ontario, Canada M6K 3E7 Distributed in Australia by Capricorn Link (Australia) Pty Ltd. P.O.

Box 6651, Baulkham Germany

Hills, Business

Printed in

All lights reserved Sterling

ISBN 0-8069-9461-4

Centre,

NSW 2153, Australia

Canada

Finland

Amethyst Ammolite

Spectrolite

Garnet Labradorite Sodalite

Venezuela Diamond

Brazil

Agate Amazonite Chalcedony

Jasper Pearls

Chrysoberyl

Diamond Emerald Garnet Opal

Guyana Diamond

Precious beryl

Argentina Rhodochrosite

Quartz Sodalite

Spodumene Topaz Tourmaline

Zimbabwe Aquamarine Chrysoberyl Emerald

Garnet Topaz Tourmaline Verdite

Russia

*-:

Alexandrite

"^\^o^

Amber Charoit.'

Diamond Emerald Feldspars

Garnet Lapis lazuli

^^ NA

S ^^r\

\ V.

^^

*

(^

i

/

Madagascar Agate Aquamarine Chrysoberyl Feldspars

Garnet Precious beryl

Quartz

Spodumene Topaz Tourmaline

Mozambique

Smoky quartz Tourmaline

Kenya Amethyst Aquamarine Garnet

Ruby Sapphire Tourmaline

India

Aquamarine Chalcedony Chrysoberyl

Burma Amber

Diamond

Chrysoberyl

Diopside

Jadeite

Tanzania Aquamarine

Emerald Garnet

Moonstone Peridot

Australia Chrysoprase

Chrysoberyl

Jasper

Rock

Coral

Diamond

Moonstone

Ruby

Emerald Garnet

Pearls

Sapphire

Emerald

Quartz Rhodonite

Spinel

Jasper

Spodumene

Nephrite

Ruby

Opal

Sapphire

Topaz Tourmaline

Sodalite

Zircon

Sapphire

Ruby Sapphire Tanzanite Tourmaline

crystal

Diamond

Pearls

"

SCIENCE/NATURE

GEMSTONES OF THE WORLD and updated with more information, more pages, more color photos than ever before!

Completely revised

Gemstones of the World, the definitive guide to gems for over 20 years, takes the mystery out of appreciating, buying,

and selling all kinds. It covers everything from the romance and history of more than 1,400 gemstones to and color and the way they are formed, structured, and mined. With many charts and diagrams, Schumann offers full coverage of the optical features of gems light and color, luminescence, refraction, and inclusions and about densities and the chemical elements of each stone, with fascinating details on different cuts, polishing, synthetic and imitation gems, hardness, cleavage, classification, trade names, rarity, and much more all with an easy-to-understand text. And then there are the magnificent photheir geographic locations, scientific, physical,

properties,

— —

—

tographs of the stones themselves in brilliant full-color, full data on the facing page. If you wanted only one book on gemstones in your library, this would be the one!

with

"Shows gems in

their

many

color photographs, with

varieties,

rough and

accompanying

tion useful to both the expert

and

text

the layman.

cut, in beautiful

which gives informa-

— Science News

// Sterling Publishing Co., Inc. New York

ISBN D-flDbT-TMbl-M 90000>

780806"994611

49725"09461