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.

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 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 Identification6 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 Techniques7 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 Liquids8 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 Identification9 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 Measurement10 Polarization and Pleochroism The Polarization of Light Polarizing Filters The Polariscope Using the Polariscope The Conoscope (Interference Figures) Pleochroism (Differential Selective Absorption) The Dichroscope11 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 Spectrophotometers12 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 Testers13 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 Gemstones14 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