COLUMBITE

hard, black (often iridescent), heavy oxide mineral of iron, manganese, and niobium [(Fe,Mn)Nb2O6]. Tantalum atoms replace niobium atoms in the crystal structure to form the mineral tantalite, which is similar but much more dense. These minerals are the most abundant and widespread of the naturally occurring niobates and tantalates and are important ores, their elements niobium and tantalum serving as constituents of corrosion-resistant metal alloys. Columbite and tantalite are found together in granite, pegmatites, and placer deposits. They occur abundantly in western Australia, Madagascar, and South Dakota, U.S. The element niobium (formerly called columbium) was first recognized in columbite and originally was named after the mineral. For detailed physical properties, see oxide mineral (table).