TABLE V
Reading edition
Character of the Refraction of Gem-Stones
(a) Single—
Diamond, spinel, garnet, opal.
Diamond and garnet frequently display local double refraction.
(b) Uniaxial, Positive—
Quartz ·009
Phenakite ·015
Benitoite ·047
Zircon (b) ·053
Quartz exhibits circular polarization.
(c) Uniaxial, Negative—
Apatite ·004
Idocrase ·005
Beryl ·007
Corundum ·009
Tourmaline ·025
(d) Biaxial, Positive—
Chrysoberyl ·007
Topaz ·009
Enstatite ·009
Spodumene ·015
Euclase ·019
Diopside ·020
Peridot ·038
Sphene ·084
(e) Biaxial, Negative—
Moonstone ·006
Iolite ·008
Axinite ·010
Andalusite ·011
Beryllonite ·012
Kyanite ·016
Epidote ·031