The mineral columbite ranges from having an iron niobium oxide chemistry to a manganese niobium oxide chemistry. The iron-rich variety is called ferrocolumbite - iron niobium oxide, FeNb2O6. Columbite also forms a chemical series with tantalite (ferrotantalite - iron tantalum oxide, FeTa2O6).
Ferrocolumbite has a submetallic to glassy luster, a black to dark red to iridescent color, a brownish black to black streak, platy or short prismatic crystals, striated crystal faces, good cleavage, is fairly hard (H = 6), not magnetic, and is quite heavy for its size. Ferrocolumbite occurs as black crystals in some pegmatitic granites, but has also been reported from some carbonatites and placer deposits.
Ferrocolumbite has economic significance - the mineral is mined and processed for the niobium metal, a rare element used in making alloys for special-use steels in various industries.
Ferrocolumbite from Keystone, Pennington County, South Dakota, USA (CSM # TM12314, Colorado School of Mines Geology Museum, Golden, Colorado, USA).