_Pink and Lilac._—Corundum (pink sapphire), spinel (balas-ruby), tourmaline (rubellite), topaz (usually when ‘fired’), spodumene (kunzite), beryl (morganite), quartz (rose-quartz). _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 TABLE IV _Colour-Dispersion of Gem-Stones_[9]