A European Informational Website
learn more
Corundum (from Tamil kurundam) is a crystalline form of aluminium oxide and one of the rock-forming minerals. It is naturally clear, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red, while all other colors are called sapphire. In addition to its hardness, corundum is unusual for its high density of 4.02 g/cm³ which is very high for a transparent mineral composed of the low atomic mass elements aluminium and oxygen.