Sapphire is a variety of corundum, an aluminium oxide with a hardness of 9. Its crystal system is hexagonal (trigonal). It forms in prismatic, bipyramidal, rhombohedral or tabular crystals, and it can also occur in granular or massive habits. It is found in metamorphic and igneous rocks, as well as alluvial deposits. Fine Sapphires have been discovered in India, Sri Lanka, Cambodia, Thailand, Madagascar, Tanzania, Pakistan, Afghanistan, East Africa and Australia. In the USA, beautiful pale blue and violet Sapphires, as well as a pastel palette of other colors, have been found in Yogo Gulch, Montana.