COLUMBITE

    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

Columbite in the World

Very beautiful crystals come from Pakistani and Afghan pegmatites with perfectly formed crystals of several centimeters on white albite. Perfect crystals of more than 10 cm and several kilos are known in and around Haddam (Connecticut) as well as in Minas Gerais (Brazil) up to 15 cm.

Right photo : Columbite from Strickland quarry, Connecticut, USA © David L. Busha

Columbite in France

In France, columbite is found in Echassières (Allier), Puy-les-Vignes (Haute-Vienne), Montebras (Creuse) as well as in a few other small localities.

Twinning

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

Fakes and treatments

No fake identified for this mineral species.



Hardness : 7
Density : 5.2 to 8
Fracture : Irregular
Streak : Black to brown


TP : Opaque to transparent
RI : 2.33 to 2.40
Birefringence : -
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None


Solubility : None


Magnetism : Paramagnetic
Radioactivity : None