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(from Latin columbium, an alternate name for niobium), a mineral of the columbite-tantalite group, combining complex oxides of the AB2O6 type and forming the isomorphic series FeNb2O6—MnNb2O6 (columbite proper) and FeTa2O6—MnTa2O6 (tantalite). The columbites also include members of isomorphic series in which niobium (in weight percent) predominates over tantalum.
The varieties of columbite include tantalocolumbite (20–40 percent Ta2O5), ferrocolumbite (FeO : MnO > 3 : 1), manganocolumbite (MnO : FeO > 3:1), magnesiocolumbite (FeO < MgO > MnO), and ixiolite (to 13 percent SnO2). In addition to the basic components, columbite almost always contains admixtures of titanium, tungsten, rare earth elements, uranium, thorium, and zirconium. Columbite crystallizes in the rhombic system. Its structure is based on the closest possible hexagonal (double-layered) packing of oxygen atoms, in the alternating layers of which the octahedral spaces are occupied in turn by (Nb, Ta) and (Fe, Mn). Columbite crystals are short prismatic, thin tabular, or tabular. They are black, brownish black, or, less often, reddish brown (manganocolumbites). The hardness of columbite is 6.0 on the mineralogical scale; the density, 5,150–6,350 kg per cu m (tantalocolumbites). Genetically, columbite is related to the quartz-bearing subalkaline syenites and the acidic alaskites, biotites, and binary granites, and particularly, to their pegmatitic and postmagmatic pneumatolytic and hydrothermal derivatives. Columbite is a source of niobium.