Gemmology - 1st Edition - ISBN: 9780750610667, 9781483144672


1st Edition

Authors: P. G. Read
eBook ISBN: 9781483144672
Imprint: Butterworth-Heinemann
Published Date: 29th March 1991
Page Count: 370
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Gemmology is a text for students preparing for the Gemmological Association's Preliminary and Diploma examinations. The book is more expansive and up-to-date than the author's earlier book, Beginner's Guide to Gemmology.
The book deals with the practical and theoretical sides of gemmology. Tracing the background and science of gemmology, the book covers the gem material, geological formation, and occurrence of gemstones on the earth. The composition of gemstones from the atoms, elements, molecules, and compounds comprising them is analyzed, and the relationship between chemical composition and durability of the stone is explained. The basics of crystallography is mentioned as a tool toward understanding gemmology after which cleavage, parting, and fracture are done. A gemstone's durability and hardness and how the latter influences engineering tests and the mining techniques are compared. An important test technique to identify unmounted stones is the measure of specific gravity using displacement measurement methods and hydrostatic methods. After more descriptive details are given in identification of gemstones, whether these are synthetic or simulants, through a comprehensive explanation of the materials found in these other gemstones, the fashioning, through shaping or polishing, of gemstones is explained. Emphasis is given on the critical angle in which light rays pass in different rock densities, and then the cutting styles, gemstone polishing, and grading are discussed.
Students studying for the Gemmological Association's Preliminary and Diploma examinations, jewelers, lapidarists, and diamond cutters, as well as those engaged in the hobby of gemmology, will find this book helpful and full of information toward their endeavors and hobbies.

Table of Contents

1 Introduction

The Evolution of the Science of Gemmology

Highlights of the Last 150 Years

The Essential Qualities of a Gem Material

Organic and Inorganic Gems

2 The Geological Formation and Occurrence of Gemstones

The Earth's Structure

Minerals and Rocks

The Formation of Gemstones in the Earth's Crust

Groups, Species and Varieties

The Major Gem Occurrences of the World

Mining Techniques

3 The Chemical Composition of Gemstones

Atoms, Elements, Molecules and Compounds



The Relationship between Chemical Composition and Durability

4 Crystallography

Crystalline and Non-crystalline Materials

The Atomic Structure of a Crystal

Classification of Crystals by Symmetry

The Seven Crystal Systems and Their Elements of Symmetry

Crystal Forms

Crystal Habits and Their Use in Identification

Twinned Crystals

Polycrystalline and Microcrystalline Minerals

Metamict Minerals

Defining Crystallographic Features by Indices

5 Cleavage, Parting and Fracture

The Mechanism of Cleavage

Lapidary Problems Caused by Cleavage Planes

The Use of Cleavage in the Fashioning of Diamond

Parting (False or Pseudo-Cleavage)

Fracture and Its Use as an Aid to Identification

6 Hardness

The Durability of a Gemstone

Mohs' Scale of Comparative Hardness

Hardness Tests (Using Hardness Pencils and Plates)

Directional Hardness

Engineering Hardness Tests

The Influence of Hardness on Mining Techniques

7 Specific Gravity, Density and Relative Density


Archimedes' Principle and the Measurement of Specific

Measurement of SG by Displacement

Hydrostatic Methods of SG Measurement

Approximation of SG Using Heavy Liquids

Safety Precautions

Precise Measurement of SG Using Heavy Liquids

8 Color, Luster and Sheen

The Electromagnetic Spectrum

The Photon

Color and Selective Absorption

Allochromatic and Idiochromatic Gems

The Transition Elements

Color-Change Gemstones

Interference Colors


Color Centers



Color, Transparency and Identification

9 Reflection and Refraction

Snell's Laws of Reflection and Refraction

Refractive Index

Double Refraction

The Refractometer

Contact Fluid

Sources of Illumination

Using the Refractometer

Optic Axes, Optic Sign and Optical Character

Distant Vision Method

Special Refractometer Versions

Fresnel's Reflectivity Equation

The Reflectance Meter

Other Methods of RI Measurement

10 Polarization and Pleochroism

The Polarization of Light

Polarizing Filters

The Polariscope

Using the Polariscope

The Conoscope (Interference Figures)

Pleochroism (Differential Selective Absorption)

The Dichroscope

11 Spectroscopy

Absorption and Emission Spectra

The Prism Spectroscope

The Diffraction Grating Spectroscope

Using the Spectroscope

Fine Line Spectra

Fraunhofer Lines

Other Spectroscope Versions

Raman Spectroscopy


12 Luminescent, Electrical and Thermal Properties of Gemstones

Luminescence (Fluorescence and Phosphorescence)

Photoluminescence and Stokes' Law

Crossed Filters

Long-Wave and Short-Wave Ultraviolet Radiation

X-Ray Radiation

Photoluminescent Properties of Gemstones

Other Forms of Luminescence

SW UV Transmission Test

Electrical Properties

Thermal Conductivity and Thermal Inertia

Thermal Conductance Testers

13 The Hand Lens, Microscope and Chelsea Filter

Types of Hand Lens

Types of Microscope

Light-Field, Dark-Field and Incident Illumination

Pin-Point Illumination and Shadowing Techniques

Immersion Techniques

Additional Uses for the Microscope

Care in the Use of the Microscope

The Chelsea Filter

Handling Gemstones

14 Gemstone Enhancement

Foils, Color Backing and Dyeing


Heat Treatments

Surface Diffusion

Irradiation Methods

Glass Filling

Laser Drilling of Diamond

Disclosure of Enhancements

15 Synthetic Gemstones and Gemstone Simulants

A Brief History of Early Gemstone Synthesis


The Verneuil Flame-Fusion Process

The Czochralski Method

Flux-Melt Growth

Zone Melting

The Hydrothermal Process

The Skull-Crucible Process

Diamond Synthesis

'Synthetic' Lapis Lazuli, Turquoise and Opal

Synthetic Jadeite

Gemstone Simulants

Composite Gemstones

Thin Diamond Films

16 Distinguishing between Synthetic and Natural Gemstones

Growth Lines and Color Zoning


Types of Inclusion

Identification Features of Natural and Synthetic Gemstones

Color Zone Diffusion and Induced Feathers/Fingerprints

Use of the Polariscope (Identifying Synthetic Quartz and Verneuil Corundum)

Laboratory Equipment and Methods

17 Identifying Inorganic Gemstone Simulants




Additional Tests for Diamond



Lapis Lazuli






18 Organic Gem Materials and Their Simulants

Natural Pearls

Cultured Pearl

Distinguishing Natural from Cultured Pearls

Imitation Pearls and Their Identification








19 The Fashioning of Gemstones

Critical Angle

Cutting Styles

Gemstone Polishing

Lapidary Techniques

Gemstone Carving

Diamond Polishing Methods

Diamond Grading


A Bibliography

B The Organic Gems

C The Inorganic Gems

D Man-Made Gems Not Occurring in Nature

E Color Theory

F Examination Notes and Sample Examination Papers

G Gemstone Constants

H Units of Measurement

I Table of Elements

J Table of Principal Fraunhofer Lines

K Gemstone Weighing



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About the Author

P. G. Read

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