Minerals and Metals in Ancient India v2.c43.s1.t1.4

v2.c43.s1.t1.4

| 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 | usually colourless | 9 | Pure Al₂O₃ is colourless. Trace impurities make it ruby or sapphire. |
| 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 padparadsca (Mg²⁺ and Cr⁴⁺ replacing two Al³⁺ ions); same colour (due to Ni and Cr); yellow karundaka (only Ni); green (due to Co, V and/or Ni); asterism or star sapphire (due to Ti). |
| Chrysoberyl/Cat's eye marjaraṣaka/laśunia | green/yellow | 8-½ | 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/puṣparāga also puṣyarāga | Yellow | 8 | Pure topaz is colourless [Al(F,OH)]₂ SiO₄. Yellow colour is due to impurities — ferrous oxide, lime and alkali. Dichroic, also blue. |
| Beryl/vaiḍūrya | Faint green water colour | 7-¾ | Pure beryl Be₃ Al₂ Si₆O₁₈ is colourless. Faint green due to substituting Cr³⁺. This is allochromatic effect — transition involving ligand field. |
| Emerald/marakata panna | Deep grass green | 7-¾ | This is beryl containing more Cr³⁺ imparting green colour. Dichroic, the second bluish colour is due to iron. |