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Orthoclase, 210
labradorescent, 212 Sunstone, 212
P.
Pastes, cutting, 74
Egyptian, 67 engraved, 68 production of, 68
Pavilions, 53
Pearls, artificial, 75
Pechopal, 181
Peridot, 254
Ceylonese, 277
Peristerite, 214
Peruvian Emerald, 233
Phenakite, 254
Phosphorescence, 30
Picotite, 198
Pin Point Opal, 178
Pinking, 263
Pipes, volcanic, 109
Pitt Diamond, 54
Plasma, 164
Pleochroism, 30
Pleonaste, 198
Point cut, 51, 55
Polarisation of light, 28
Polishing, 64
dangers of, 65
Prase, 164
Precious Amethyst, 153 Beryl, 229 Garnet, 246, 248 Opal, 177 Serpentine, 281
Prehnite, 273
origin of, 11
Prime d'Amethyst, 155
Prince Rupert's drops, 96
Pyroelectricity, 34
Pyrope, 246
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Q. Quartz, 146
applications of, 150
Asteriated, 152
Aventurine, 159
Cat's Eye, 158
containing other substances, 160
Iridescent, 152
Iris, 152
Milky, 157 origin of, 11
Rainbow, 152
Rose, 155 Sagenitic, 157
Sapphire, 157
Smoky, 156
staining of, 151
Star, 152
Yellow, 155
R.
Rainbow Quartz,
152 Refraction, double, 27 index of, 24 measurement of, 26 single, 23
Refractive indices, table of, 32 Refractometer, 26 Resin Opal, 181
Rhodolite, 250 Ribbon Agate, 168, 174 Ring Agate, 168 ; Rock Crystal,
149 drills, 131 Ruby, 246 Rontgen rays, 32 Rose cut, 51, 55
Quartz, 155 Rosette, 55 Rubellite, 276
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