Alumina << uh LOO muh nuh >>, also called aluminum oxide, is a compound composed of aluminum and oxygen. Alumina occurs in nature as a mineral called corundum. Alumina and water occur in different combinations in the minerals boehmite, diaspore, and gibbsite. These minerals are found in bauxite, the chief source of the alumina from which manufacturers make aluminum.
Refined alumina has wide use as an abrasive, a material used for grinding and polishing. Alumina resists high temperatures and is a poor conductor of electricity, and so it is used in furnace linings and electrical insulators. A white clay called kaolin, which contains alumina, is used in making porcelain dinnerware.
Alumina occurs in several crystal forms. These forms have the same chemical formula but differ in the arrangement of their aluminum and oxygen atoms. The various forms can be changed from one to another by heating them to certain temperatures.
