Minerals and Metals in Ancient India v2.c47.45

v2.c47.45

*Corundum* : Aluminium oxide. Al₂O₃. White if pure. Many varieties of different colours due to traces of specific impurities. Sapphire is blue (due to Ti, Fe & Co). True or Oriental Ruby is red. Oriental Topaz Yellow. Oriental Emerald green Amethyst purple. The term sapphire is used in general sense for all colours except red. Asteriated or *Star Sapphire* shows stallate opalescence or asterism which is due to the presence of minute cylindrical cavities which lie parallel to the prism planes. Adamantine Spar from India is dark to translucent corundum, looking greenish or bluish by transmitted light. Emery is granular corundum. May be black or grey due to intimate association of magnetite or hematite.