Bauxite is a rock formed in wet, tropical climates when soluble materials leach into silica rocks. Bauxite is the principle ore from which most of the world's pure aluminum is extracted for commercial use. As of 2010, the largest producers of bauxite are Australia, China, Brazil, India, Guinea, Jamaica and Russia. Some of these countries have enough reserves for more than 100 years of aluminum production.
The color of bauxite ranges from dirty white to grey, brown, red and yellow. Other physical properties include a hardness of 1.0 to 3.0 on the Mohs scale, making bauxite one of the softest rocks on Earth. Bauxite contains impurities of iron, titanium and phosphorous.
Commercial-grade bauxite contains 25- to 30-percent aluminum oxide, which is extracted in a solution of sodium hydroxide. Once aluminum oxide is created, it is dissolved in a molten bath of cryolite to produce pure aluminum. This process takes enormous amounts of electricity, so pure aluminum is made in areas with low energy costs.
Aluminum oxide, or alumina, also comes from bauxite and is used as industrial abrasives. Alumina, unlike bauxite, is very hard with a Mohs hardness of nine, with 10 measuring the hardest substance on Earth. Crushed bauxite is used in sandblasting applications.
Bauxite is named after Les Baux de Provence in France, the location where the rock was first recognized as aluminum ore.