Metallic and adamantine lustres are connected with high refractive indices. The colours of precious stones are discussed in chapter iv.
In the five tables which follow have been arranged certain physical data of precious stones so that they may be discriminated from one another by comparing their specific gravities, their behaviour when examined with the dichroiscope, and their hardness.
DISCRIMINATION OF PRECIOUS STONES.
WHITE STONES.
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NAME. DENSITY. PLEOCHROISM. HARDNESS.
Opal 2·20 None 6
Moonstone 2·58 None„ 6
Rock-cryystal 2·65 None„ 7
Beryl 2·69 None„ 7¾
Phenakite 2·98 None„ 7¾
Diamond 3·53 None„ 10
Topaz 3·57 None„ 8
Sapphire 4·00 None„ 9
Zircon 4·75 None„ 7½
RED AND PINK STONES.
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NAME. DENSITY. PLEOCHROISM. HARDNESS.
Tourmaline 3·05 Strong 7¼
Kunzite 3·18 Strong„ 6¾
Topaz 3·53 Strong„ 8
Spinel 3·58 None 8
Pyrope 3·75 None„ 7½
Ruby 4·00 Strong 9
Almandine 4·15 None 7½
Zircon 4·70 Weak 7½
