| Columbite-(Fe) | |
|---|---|
| General | |
| Category | Oxide minerals |
| Chemical formula | Fe2+Nb2O6 |
| Strunz classification | 04.DB.35 |
| Identification | |
| Color | Black, brownish black. |
| Crystal habit | Massive - Granular - Common texture observed in granite and other igneous rock; Striated - Parallel lines on crystal surface or cleavage face. |
| Crystal system | Orthorhombic, (2/m 2/m 2/m), SpaceGroup = Pcan |
| Cleavage | [010] Distinct |
| Fracture | Sub Conchoidal - Fractures developed in brittle materials characterized by semi-curving surfaces. |
| Mohs scale hardness | 6 |
| Luster | sub-metallic |
| Streak | blackish brown |
| Specific gravity | 5.3 - 7.3, Average = 6.3 |
| Optical properties | Biaxial (+), b=2.29-2.4 |
| Other characteristics | non-radioactive, non-fluorescent. |
| References | [1][2] |
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 in Haddam, 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.[3]
Columbite is also very similar to tapiolite. Those minerals have same chemical composition but different crystal symmetry: orthorhombic for columbite and tetragonal for tapiolite.[4] The largest documented single crystal of columbite consisted of plates 6 millimetres (0.24 in) thick measuring 76 by 61 centimetres (30 × 24 in).[5]
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