Gemmology

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.

Contenu

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
Valency
Bonding
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
Definitions
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
Dispersion
Color Centers
Lustre
Sheen
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
Spectrophotometers
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
Impregnation
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
Definitions
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
Twinning
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
Alexandrite
Aquamarine
Diamond
Additional Tests for Diamond
Emerald
Jade
Lapis Lazuli
Turquoise
Opal
Quartz
Ruby
Sapphire
18 Organic Gem Materials and Their Simulants
Natural Pearls
Cultured Pearl
Distinguishing Natural from Cultured Pearls
Imitation Pearls and Their Identification
Shell
Amber
Ivory
Odontolite
Tortoiseshell
Jet
Coral
19 The Fashioning of Gemstones
Critical Angle
Cutting Styles
Gemstone Polishing
Lapidary Techniques
Gemstone Carving
Diamond Polishing Methods
Diamond Grading
Appendices
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
Index