Columbite
| Columbite-(Fe) | |
|---|---|
 |
|
| General | |
| Category | Oxide minerals |
|
Formula (repeating unit) |
Fe2+Nb2O6 |
| Strunz classification | 4.DB.35 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pbcn |
| 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. |
| 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 | |
Columbite, also called niobite, niobite-tantalite and columbate [(Fe, Mn)Nb2O6], is a black mineral group that is an ore of niobium. It has a submetallic luster and a high density and is a niobate of iron and manganese. This mineral group was first found in Haddam, Connecticut, in the United States. 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 (orthorhombic) 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 mm (0.24 in) thick measuring 76 cm × 61 cm (30 in × 24 in).
The occurrence of columbite in the United States was made known from a specimen presumably stemming from John Winthrop (1606–1676), first Governor of the Connecticut Colony and avid mineral collector. Amidst 600 other samples, it was donated by his namesake and grandson, John Winthrop (1681–1747) to Hans Sloane, President of the Royal Society of Great Britain, upon becoming a Fellow of the Royal Society in 1737.
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