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Columbite, also called niobite, niobite-tantalite and columbate [(Fe, Mn)(Nb, Ta)2O6], is a black mineral group that is an ore of niobium and tantalum. It has a submetallic luster and a high density and is a niobate of iron and manganese, containing tantalate of iron. This mineral group was first found at Haddam, Middlesex County, Connecticut, in New England, USA. It forms a series with the tantalum-dominant analogue ferrotantalite and one with the manganese-dominant analogue manganocolumbite. The iron-rich member of the columbite group is ferrocolumbite. Some tin and tungsten may be present in the mineral. Yttrocolumbite is the yttrium-rich columbite with the formula (Y,U,Fe)(Nb,Ta)O4. It is a radioactive mineral found in Mozambique.
Columbite has the same composition and crystal symmetry (orthorombic) as tantalite. In fact, the two are often grouped together as a semi-singular mineral series called columbite-tantalite or coltan in many mineral guides. However, tantalite has a much greater specific gravity than columbite, more than 8.0 compared to columbite's 5.2.
Columbite is also very similar to tapiolite. Those minerals have same chemical composition but different crystal symmetry: orthorhombic for columbite and tetragonal for tapiolite. The largest documented single crystal of columbite consisted of plates 6 millimetres (0.24 in) thick measuring 76 by 61 centimetres (30 in × 24 in).
1. ^ Columbite-(Fe) Mineral Data