Columbite << kuh LUHM byt >> is a black, dense mineral made up of iron, manganese, niobium, oxygen, and, in some cases, tantalum. It is the chief source of niobium, which is used in some steels. The composition of columbite varies widely, with tantalum taking the place of different amounts of niobium. A similar mineral that has more tantalum than niobium is called tantalite. The crystal structure of columbite is orthorhombic, with three sets of unequal rectangular faces (see Crystal (Classifying crystals)). Columbite occurs in coarse granitic rocks called pegmatites. It is mined in Brazil and several African countries.
