Bauxite. Credit: Mineral Information Institute.
Bauxite is the main ore of aluminum – the source of over 99% of the metal. It is the name for a mixture of similar minerals that contain hydrated aluminum oxides; usually iron oxide is present as an impurity. These minerals are gibbsite (Al(OH)3), diaspore (AlO(OH)), and boehmite (AlO(OH)). Because it is a mixture of minerals, bauxite itself is a rock, not a mineral. It is reddish-brown, white, tan, and tan-yellow. It is dull to earthy in luster and can look like clay or soil. Bauxite forms when silica in aluminum-bearing rocks (that is, rocks with a high content of the mineral feldspar) is washed away.
High-grade bauxite, being highly refractory, is used as a lining for furnaces. Synthetic corundum is made from it, and it is an ingredient in some quick-setting cements.
Australia has huge reserves of bauxite, and produces over 40% of the world's ore. Brazil, Guinea, and Jamaica are important producers, with lesser production from about 20 other countries.