Gemmology

by Read, Peter G.

• ISBN13: 9780750610667
• ISBN10: 0750610662
• eBook ISBN(s): 9781483144672
• Format: Hardcover
• Copyright: 1991-02-01
• Publisher: Butterworth-Heinemann (Sd)

Table of Contents

Preface	p. ix
Acknowledgements	p. x
Introduction	p. 1
The evolution of the science of gemmology	p. 1
Highlights of the last 160 years	p. 1
The essential qualities of a gem material	p. 9
Organic and inorganic gems	p. 10
The geological formation and occurrence of gemstones	p. 11
The Earth's structure	p. 11
Minerals and rocks	p. 12
The formation of gemstones in the Earth's crust	p. 12
Groups, species and varieties	p. 15
The major gem occurrences of the world	p. 16
Mining techniques	p. 18
The chemical composition of gemstones	p. 21
Atoms, elements, molecules and compounds	p. 21
Valency	p. 23
Bonding	p. 24
The relationship between chemical composition and durability	p. 26
Crystallography	p. 28
Crystalline and non-crystalline materials	p. 28
The atomic structure of a crystal	p. 30
Classification of crystals by symmetry	p. 32
The seven crystal systems and their elements of symmetry	p. 33
Crystal forms	p. 37
Crystal habits and their use in identification	p. 38
Twinned crystals	p. 40
Polycrystalline and microcrystalline minerals	p. 41
Metamict minerals	p. 42
Defining crystallographic features by indices	p. 43
Cleavage, parting and fracture	p. 44
The mechanism of cleavage	p. 44
Lapidary problems caused by cleavage planes	p. 45
The use of cleavage in the fashioning of diamond	p. 47
Parting (false or pseudo-cleavage)	p. 47
Fracture and its use as an aid to identification	p. 47
Hardness	p. 49
The durability of a gemstone	p. 49
Mohs' scale of comparative hardness	p. 49
Hardness tests (using hardness pencils and plates)	p. 50
Directional hardness	p. 52
Engineering hardness tests	p. 53
The influence of hardness on mining techniques	p. 54
Specific gravity, density and relative density	p. 55
Definitions	p. 55
Archimedes' principle and the measurement of SG	p. 55
Measurement of SG by displacement	p. 56
Hydrostatic methods of SG measurement	p. 58
Approximation of SG using heavy liquids	p. 62
Safety precautions	p. 67
Precise measurement of SG using heavy liquids	p. 68
Colour, lustre and sheen	p. 69
The electromagnetic spectrum	p. 69
The photon	p. 70
Colour and selective absorption	p. 71
Allochromatic and idiochromatic gems	p. 72
The transition elements	p. 72
Colour-change gemstones	p. 73
Interference colours	p. 74
Dispersion	p. 74
Colour centres	p. 75
Lustre	p. 76
Sheen	p. 76
Colour, transparency and identification	p. 80
Reflection and refraction	p. 81
Snell's laws of reflection and refraction	p. 81
Refractive index	p. 82
Double refraction	p. 83
The refractometer	p. 84
Contact fluid	p. 86
Sources of illumination	p. 86
Using the refractometer	p. 88
Optic axes, optic sign and optical character	p. 90
Distant vision method	p. 93
Special refractometer versions	p. 94
Fresnel's reflectivity equation	p. 95
The reflectance meter	p. 96
Other methods of RI measurement	p. 99
Polarization and pleochroism	p. 107
The polarization of light	p. 107
Polarizing filters	p. 107
The polariscope	p. 109
Using the polariscope	p. 111
The conoscope (interference figures)	p. 112
Pleochroism (differential selective absorption)	p. 113
The dichroscope	p. 114
Spectroscopy	p. 117
Absorption and emission spectra	p. 117
The prism spectroscope	p. 118
The diffraction grating spectroscope	p. 120
Using the spectroscope	p. 122
Fine line spectra	p. 126
Fraunhofer lines	p. 127
Other spectroscope versions	p. 127
Raman spectroscopy	p. 129
Spectrophotometers	p. 129
Luminescent, electrical and thermal properties of gemstones	p. 131
Luminescence (fluorescence and phosphorescence)	p. 131
Photoluminescence and Stokes' law	p. 132
Crossed filters	p. 132
LW and SW UV radiation	p. 133
X-ray radiation	p. 135
Photoluminescent properties of gemstones	p. 136
Other forms of luminescence	p. 136
SW UV transmission test	p. 138
Electrical properties	p. 139
Thermal conductivity and thermal inertia	p. 141
Thermal conductance testers	p. 142
The hand lens, microscope and Chelsea filter	p. 145
Types of hand lens	p. 145
Types of microscope	p. 147
Light-field, dark-field and incident illumination	p. 150
Pin-point illumination and shadowing techniques	p. 151
Pin-point illumination and shadowing techniques	p. 151
Immersion techniques	p. 152
Additional uses for the microscope	p. 153
Care in the use of the microscope	p. 154
The Chelsea filter	p. 155
Handling gemstones	p. 156
Gemstone enhancement	p. 160
Foils, colour backing and dyeing	p. 160
Implanation	p. 161
Heat treatments	p. 162
Surface diffusion	p. 165
Irradiation methods	p. 166
Glass filling	p. 169
Laser drilling of diamond	p. 170
Disclosure of enhancements	p. 170
Synthetic gemstones and gemstone simulants	p. 172
A brief history of early gemstone synthesis	p. 172
Definitions	p. 173
The Verneuil flame-fusion process	p. 173
The Czochralski method	p. 177
Flux-melt growth	p. 178
Zone melting	p. 180
The hydrothermal process	p. 180
The skull-crucible process	p. 184
Diamond synthesis	p. 185
'Synthetic' lapis lazuli, turquoise and opal	p. 188
Synthetic jadeite	p. 189
Gemstone simulants	p. 189
Composite gemstones	p. 189
Thin diamond films	p. 192
Distinguishing between synthetic and natural gemstones	p. 193
Growth lines and colour zoning	p. 193
Twinning	p. 193
Types of inclusion	p. 194
Identification features of natural and synthetic gemstones	p. 194
Colour zone diffusion and induced feathers/fingerprints	p. 208
Use of the polariscope (identifying synthetic quartz and Verneuil corundum)	p. 208
Laboratory equipment and methods	p. 209
Identifying inorganic gemstone simulants	p. 216
Alexandrite	p. 217
Aquamarine	p. 217
Diamond	p. 218
Additional tests for diamond	p. 219
Emerald	p. 222
Jade	p. 222
Lapis lazuli	p. 223
Turquoise	p. 223
Opal	p. 224
Quartz	p. 225
Ruby	p. 225
Sapphire	p. 226
Organic gem materials and their simulants	p. 227
Natural pearls	p. 227
Cultured pearls	p. 229
Distinguishing natural from cultured pearls	p. 232
Imitation pearls and their identification	p. 236
Shell	p. 239
Amber	p. 240
Ivory	p. 242
Odontolite	p. 243
Tortoiseshell	p. 243
Jet	p. 244
Coral	p. 245
The fashioning of gemstones	p. 247
Critical angle	p. 247
Cutting styles	p. 250
Gemstone polishing	p. 256
Lapidary techniques	p. 256
Gemstone carving	p. 258
Diamond polishing methods	p. 259
Diamond grading	p. 263
Appendices	p. 267
Bibliography	p. 267
The organic gems	p. 268
The inorganic gems	p. 270
Man-made gems not occurring in nature	p. 291
Colour theory	p. 293
Examination notes and sample examination papers	p. 295
Gemstone constants	p. 302
Units of measurement	p. 306
Table of elements	p. 307
Table of principal Fraunhofer lines	p. 310
Gemstone weighing	p. 310
Index	p. 313
Table of Contents provided by Syndetics. All Rights Reserved.