Its name comes from the Indian words kauruntaka, kurundam, karand and the Sanskrit kurivinda meaning red. The ancient Greeks called it
Corundum is the second hardest material in nature, after diamond. Ancient writers note its usefulness in lithography for making seal stones and ring stones. Pliny and other Roman writers call it naxium. Dioscorides describes it as 'a smyris stone, or the ring-glyphs'. It has an adamantine or vitreous lustre and its transparency ranges from transparent to translucent. It is found in shades of brown, red, green, yellow, grey and colourless. The colourless variant of Corundum is called white sapphire. The transparent variant is made up of the gemstones: ruby and sapphire. The red colour of ruby is due to chromium impurities, while the blue colour of sapphire is due to iron and titanium impurities. The opaque variant is emery, which is an important industrial material used in the manufacture of sandpaper and abrasive wheels. It belongs to the oxide minerals and the triangular crystallographic system. It is often found with calcite, zoisite, feldspar, feldspar, mica, mica, cyanite, syllymanite, magnetite (mainly in emerald) and minerals of the garnet group. Corundum sources are found in many parts of the world. Its valuable variants are found in Myanmar and Sri Lanka. Also, in many places in Africa, India, USA, Brazil, Turkey and Madagascar. In Greece, especially in Apeiranthos and the surrounding Naxian villages, Korundio is found in the form of emery. For more than 2500 years, the Naxian land has been an important place of mining of the mineral worldwide.
