Columbite. Credit: Smithsonian Institution.
Columbite is a lustrous black oxide mineral of iron, manganese, and niobium [(Fe, Mn) Nb2O6]. It is the chief ore of niobium and is found in granite pegmatites mainly in Western Australia, Zaire, Madagascar, and South Dakota. Tantalum replaces niobium in all proportions up to 100% (tantalite). Columbite crystallizes in the orthorhombic system, forming prismatic crystals with one distinct cleavage. Hardness 6.0 to 6.5. Relative density 5.2 (columbite) to 8.0 (tantalum).