Most gems-quality corundum that is not red is called Sapphire. The name is popularly associated with the color blue, but many variety colors of sapphire corundum can be black, green, yellow, orange (padparacha sapphire), and pink.
Good quality sapphire is found in Burma, Sri Lanka, and India. Most of sapphire found in Thailand, Australia, and Nigeria are dark blue, may appear nearly Black. The rutile inclusions on sapphire stone create 6-rayed star effect when it is cut in cabochons.
Crystal Structure
Trigonal
Composition
Aluminium Oxide
Hardness
9
source: from many sources
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