History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c17.s3.t1.4

v1.c17.s3.t1.4

| Name English/Sanskrit | Colour | Hardness (Moh's Scale) | Reasons for non-white colour |
| Zircon/*Gomed* | Cow-flesh colour | 7 1/2 | Pure zircon ZrSiO4 is colourless. Reddish-yellow colour of Hyacinth is due to Fe3+ decolourised on reduction to Fe2+ |
| Garnet/*Tāmrya* or *Tāmḍi* | Various colours | 7 1/4 | Family of minerals M2+3 M3+2. (SiO4)3 . Colour depends upon chemical composition. Hessonite is confused with Hyacinth. Colour due to iron. |
| Tourmaline/*Vaikrāntā* | Various colours | 7 1/4 | H9 Al3 (B.OH)2 Si4O19 pure tourmaline is light coloured. Fe2+ and Cr3+ make it dark green, Mg makes it brown and Mn dark red. |
| Quartz/*Sphaṭika* | Colourless | 7 | Pure SiO2 is colourless. Yellow citrine due to iron green chrysoprase due to nickel, violet amethyst due to manganese etc. |
| Agate/*Akik* | Light colour | 6 1/2 | Hydrated SiO2 is colourless Hydrated ferric oxide as impurity makes it brown or yellow. |
| Carnelian/*Rudhirakhya* | Red | | Heating causes dehydration and ferric oxide gives red colour to carnelian. |
| Olivine/Chrysolite/Peridot *Puttika/Jabarjad* | Bottle green | 6 1/2 | Pure Mg2SiO4 is colourless Replacement of part of MgO by ferrous oxide makes it yellowish green. Mn2+..N i2+ further change the colour. |
| Orthoclase/Feldspar Moonstone/*Candrakāntā* Sunstone/*Sūryakāntā* | Opalescent play of colour | 6 | Interference of light from thin layers. |
| Jade/*Pīlu* | White green black | 5 1/2 - 7 | Green due to Mn and Cr and Fe2+. Black due to Fe3+ |