Red.—Corundum (ruby), garnet (pyrope, almandine), spinel (balas-ruby), tourmaline (rubellite), zircon, opal (fire-opal).
Green.—Beryl (emerald, aquamarine), peridot, corundum, tourmaline, chrysoberyl (including alexandrite), zircon, garnet (demantoid); among less common species, spodumene (hiddenite), euclase, diopside, idocrase, epidote, apatite, obsidian; rarely diamond; also semi-opaque, turquoise, jade.
Blue.—Corundum (sapphire), spinel, topaz, tourmaline, zircon; among the less common species, kyanite, iolite, benitoite, apatite; rarely diamond; also semi-opaque, turquoise, lapis lazuli, sodalite.
Violet and Purple.—Quartz (amethyst), corundum (oriental amethyst), spinel (almandine-spinel), garnet (almandine), spodumene (kunzite), apatite.
Brown.—Diamond, tourmaline, quartz (smoky-quartz); among the less common species, andalusite, axinite, sphene.
TABLE III
Refractive Indices of Gem-Stones[8]
| 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 | |