Columbite - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Orthorhombic
    Chemistry : (Fe²⁺,Mn²⁺,Mg²⁺)(Nb,Ta)₂O₆
    Rarity : Uncommon

Columbite, formerly called niobite, forms a continuous series with tantalite, hence the names columbo-tantalite or tantalo-columbite depending on the dominant element. These complex oxides have such variable chemical compositions that they have been promoted to the rank of groups, subdivided according to the dominant element into ferrocolumbite, manganocolumbite and magnocolumbite for the columbite group and ferrotantalite, manganotantalite for that of tantalite. Its name comes from the old name for niobium : columbium. These minerals, difficult to distinguish from each other, are found mainly in granitic pegmatites with rare elements, notably sodium-lithium (sodolithic) and sodium-potassium (sodolithic potassium) pegmatites, where they constitute usually black crystals, of size sometimes impressive weighing up to 15 kilos. Heavy (density of 5.2 to 8 depending on the mineral), hard, and almost unalterable, these minerals are also very common in alluvium where their main exploitations are located. These are essential niobium ores.

Main photo : Columbite © L

Twins are known on {021} and {023}, can produce pseudohexagonal trills.

No fake identified for this mineral species.