Corundum is a crystalline form of aluminium oxide (Al 2O 3) typ... - dofaq.co
corundum

Corundum is a crystalline form of aluminium oxide (Al 2O 3) typ...

wikipedia - 14 Sep 2015
Corundum is a crystalline form of aluminium oxide (Al 2O 3) typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors when impurities are present. Transparent specimens are used as gems, called "ruby" if red and "padparadscha" if pink-orange. All other colors are called "sapphire", e.g., "green sapphire" for a green specimen.

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