Alumina, also called alumina, is a synthetically produced alumina, Al 2 O 3, a white or nearly colorless crystalline substance that is used as a starting material for melting metallic aluminum. It also serves as a raw material for a wide range of modern ceramic products and as an active ingredient in chemical processing. Alumina is made from bauxite, a naturally occurring ore containing varying amounts of hydrous (water-containing) alumina. Free Al 2 O 3 occurs naturally as a mineral. corundum and its forms of gemstones, sapphire and ruby; they can be synthesized from alumina and in fact are sometimes referred to as alumina, but the term is more accurately limited to the material used in aluminum metallurgy, industrial ceramics, and chemical processing.