| Columbite |
 |
| General |
| Category |
Oxide mineral |
| Chemical formula |
Fe2+Nb2O6 |
| Identification |
| Molar mass |
337.66 |
| 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] |
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 specific gravity 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.[2]
Columbite is also very close to tapiolite. Those minerals have same chemical composition but different crystal symmetry: orthorhombic for columbite and tetragonal for tapiolite.[3] 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).[4]
References
See also
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