History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c17.s3.t1.5

v1.c17.s3.t1.5

| Name English/Sanskrit | Colour | Hardness (Moh's Scale) | Reasons for non-white colour |
| Turquoise | Blue | | The mineral is derivative for ortho- phosphoric acid, the hydrogen atoms replaced by radicals such as Al(OH)2 Fe(OH)2 (providing green tinge) and Cu(OH), providing intense blue colour. |
| Lapis Lazuli/Ultra-marine/ *Rajāvārtal Lajhward* | Deep azure blue | 5¹/₂ | The constituent minerals are Sodium-Calcium-Aluminium silicates with sulphate and polysulphide (S⁻3) anions. The 19 outer electrons of S⁻3 unit undergo transitions within the molecular orbitals. These produce absorption band in the yellow range and hence intense blue colour. Less sulphur in the mineral system gives green colour which makes the gem less worthy. |
| Pearl/*Mukta* | Usually white | 3-4 | Iron, manganese etc.possibly complexed with organic matter, so that the colour is perishable on heat. |
| Coral/*Pravāla/Vidruma* | red,black etc. | 3-4 | “ |