Table III
Refractive Indices of Gem-Stones8
| Opal | 1·454 | |
| Moonstone | 1·53 | 1·54 |
| Iolite | 1·543 | 1·551 |
| Quartz | 1·544 | 1·553 |
| Beryllonite | 1·553 | 1·565 |
| Beryl | 1·578 | 1·585 |
| Turquoise | 1·61 | 1·65 |
| Topaz | 1·618 | 1·627 |
| Andalusite | 1·632 | 1·643 |
| Tourmaline | 1·626 | 1·651 |
| Apatite | 1·642 | 1·646 |
| Phenakite | 1·652 | 1·667 |
| Euclase | 1·651 | 1·670 |
| Spodumene | 1·660 | 1·675 |
| Enstatite | 1·665 | 1·674 |
| Peridot | 1·659 | 1·697 |
| Axinite | 1·674 | 1·684 |
| Diopside | 1·685 | 1·705 |
| Idocrase | 1·714 | 1·719 |
| Spinel | 1·726 | |
| Kyanite | 1·72 | 1·73 |
| Epidote | 1·735 | 1·766 |
| Garnet (Hessonite) | 1·745 | |
| Chrysoberyl | 1·746 | 1·753 |
| Garnet (Pyrope) | 1·755 | |
| Benitoite | 1·757 | 1·804 |
| Corundum | 1·761 | 1·770 |
| Garnet (Almandine) | 1·790 | |
| Zircon (a) | 1·815 | |
| Garnet (Demantoid) | 1·885 | |
| Sphene | 1·901 | 1·985 |
| Zircon (b) | 1·927 | 1·980 |
| Diamond | 2·417 | |
Table IV
Colour-Dispersion of Gem-Stones9
| 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 |