History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c17.s3.t1.3

v1.c17.s3.t1.3

| Name English/Sanskrit | Colour | Hardness (Moh's Scale) | Reasons for non-white colour |
| Diamond/*Vajra* | usually colourless | 10 | Blue due to boron, yellow/green due to nitrogen |
| Corundum/*Kuruvinda* | “ | 9 | Pure Al₂O₃ is colourless |
| Ruby *Padmarāga* | red | 9 | Cr³⁺ replaces Al³⁺. Transition involving ligand field effect |
| Sapphire *Indranīla* | blue | 9 | Four different mechanisms including charge transfer, combination of Fe and Ti |
| Non-blue Sapphire | | 9 | Orange |
| Chrysoberyl/Cat’s eye *Marjaraksaka/Lasunia* | Green/Yellow | 8¹/₂ | Green due to Cr and yellow due to Fe substituting in Be Al₂O₄ structure. |
| Spinel/Balas-ruby/ *Bālasūryaka* | rose-red | 8 | Pure spinel Mg Al₂O₄ is colourless. Cr³⁺ substitution makes it rose-red. Fe and Mg may further alter the colour. |
| Topaz/*Pusparāga* | Yellow | 8 | Pure topaz is colourless [Al (F,OH)]₂ SiO₄. Yellow colour is due to impurities - ferrous oxide lime and alkali. Dichromic also blue |
| Beryl/*Vaidūrya* | Faint green water colour | 7³/₄ | Pure beryl Be3 Al₂ Si₆O₁₈ is colourless. Faint green due to substituting Cr³⁺. This is allochromatic effect - transition involving ligand field. |
| Emerald/*Marakata Pānnā* | Deep grass green | 7³/₄ | This is beryl containing more Cr³⁺ imparting green colour. Dichroic, the second blueish colour is due to iron. |
| Aquamarine/*Pāribhadra* | Faint blue to bluish green | 7³/₄ | Bluish tinge due to iron |