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 |