Columbite
Columbite, also called niobite, niobite-tantalite and columbate, with a general chemical formula of (FeII,MnII)Nb2O6, is a black mineral group that is an ore of niobium. It has a submetallic luster, a high density, and is a niobate of iron and manganese. Niobite has many applications in areospace, construction and the medical industry. Dating columbite minerals is primarily completed by uranium lead (U-Pb) dating which is a time-consuming process.
| Columbite | |
|---|---|
| General | |
| Category | Oxide minerals |
| Formula (repeating unit) | (FeII,MnII)Nb2O6, or in oxide formula (FeII,MnII)O·Nb2O5 |
| IMA symbol | Clb |
| 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 | Radioactive, non-fluorescent. |
| References | |
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. The formation of Columbite is dependant on the concentrations of metals present which effect the crystalline structure of the mineral and the environmental impact.
Columbite is also very similar to tapiolite. These minerals have the 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).
Columbite contains varying amounts of thorium and uranium, which makes it radioactive to various degrees. Coltan, a tantalum dominate species of columbite, is often mined artesian and small scale miners which results environmental risks and danger to human health due to unregulated working conditions.