Bauxite

Bauxite, important ore of aluminium, consisting of aluminium oxide of various degrees of hydration. It is usually mixed with impurities, particularly iron. Among the specific aluminium-bearing minerals in bauxite are gibbsite, Al(OH)₃, and diaspore, HAlO₂. Bauxite is a soft mineral with hardness varying from 1 to 3 on the Mohs scale and relative density from 2 to 2.55. In colour it may vary from white to brown, and is dull in appearance. Bauxite usually occurs in aggregates in pea-sized lumps.

Aluminium is the commonest of all metals on the surface of the Earth. However, it occurs most frequently in the form of complex compounds such as those found in clay and granite, which cannot be used commercially as ores because of the difficulty of extracting the aluminium. Bauxite, on the other hand, which forms by the rapid weathering of granitic rocks in warm, humid climates, can be easily purified and converted directly into either alum or metallic aluminium. Bauxite is mined in large quantities in Australia, Guinea, and Jamaica.