Moonstone ·012 Quartz ·013 Beryl ·014 Topaz ·014 Chrysoberyl ·015 Tourmaline ·017 Spodumene ·017 Corundum ·018 Peridot ·020 Spinel ·020 Garnet (Almandine) ·024 Garnet (Pyrope) ·027 Garnet (Hessonite) ·028 Zircon ·038 Diamond ·044 Sphene ·051 Garnet (Demantoid) ·057 TABLE V _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 TABLE VI _Dichroism of Gem-Stones_ (_a_) STRONG Corundum, tourmaline, alexandrite, spodumene, andalusite, iolite, epidote, axinite. (_b_) DISTINCT Emerald, topaz, quartz, peridot, chrysoberyl, enstatite, euclase, idocrase, kyanite, sphene, apatite. (_c_) WEAK Beryl, diopside. TABLE VII _Specific Gravities of Gem-Stones_