Columbite

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Columbite, mineral oxide of niobium, tantalum, iron, and manganese with varying proportions of niobium and tantalum. When the proportion of tantalum exceeds that of niobium, it is called tantalite. Columbite is the principal commercial source of tantalum and niobium. It has a hardness of 6 and a specific gravity that varies from about 5 to about 8 depending on the composition. It is black to red in color, often iridescent, and is usually found in the form of orthorhombic crystals in granite and granitic pegmatite. Columbite deposits are found in Australia, Canada, Greenland, Norway, the former Union of Soviet Socialist Republics, and in several states of the United States.

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