The finest rubies come from Burma. The best sapphires are found in the alluvial deposits of Thailand, Sri Lanka and Cambodia. Corundum is used as a gemstone and abrasive. The deep red ruby is one of the most valuable of gems. Stones of gem quality are used as watch jewels and as bearings in scientific instruments.
Artifical corundum is manufactured from bauxite on a large scale.
This synthetic material, together with other manufactured abrasives, notably silicon carbide, has largely taken the place of natural corundum as an abrasive. Hematite - Fe2O3 Hematite is distinguished chiefly by its characteristic red streak. It is widely distributed in rocks of all ages and forms the most abundant and important ore of Fe. Black crystals may be cut as gems. The platy and metallic variety is known as specularite.