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 |
|
|
