BÖHMITE

    Class : Oxides and hydroxides
    Subclass : Hydroxides and hydrates
    Crystal System : Orthorhombic
    Chemistry : AlO(OH)
    Rarity : Common

Böhmite is the dimorph of diaspore ; it is formed by meteoric or hydrothermal alteration of aluminum silicates, notably nepheline. As in the diaspore, the aluminum can be very partially replaced by iron. Its name is dedicated to the German paleontologist Johannes Böhm who identified the mineral by X-ray diffraction. It generally occurs in cryptocrystalline aggregates of pisolithic appearance, sometimes massive, it can be found in tiny flattened lenticular crystals not exceeding 2 mm. Böhmite is usually colorless, white, yellowish to grey-yellow, sometimes brown when iron contents exceed 1%. It is one of the essential components of bauxites, primarily those formed by the weathering of nepheline syenites (Guinea deposits) in a tropical climate. It is mined as an aluminum ore and used in the manufacture of refractory materials.

Main photo : Böhmite from Saga 1 Quarry, Vestfold og Telemark, Norway © OT. Ljostad

Böhmite from Saga 1 Quarry, Vestfold og Telemark, Norway © Joachim Esche
Böhmite and green diaspore from Saga 1 Quarry, Norway © OT. Ljostad
Böhmite from Saga 1 Quarry, Vestfold og Telemark, Norway © Chinellato Matteo
Böhmite from Saga 1 Quarry, Vestfold og Telemark, Norway © Marko Burkhardt

Böhmite in the World

Böhmite is found in all bauxite deposits (USA, Cuba, Guinea, etc.) and as a hydrothermal retromorphosis mineral in most nepheline syenite massifs. The best crystals also come from the latter such as the Saga 1 quarry (Norway), they are millimetric and lenticular.

Böhmite in France

In France, böhmite is abundant in the old bauxite deposits of Cadarcet (Ariège) and Baux-de-Provence (Bouches-du-Rhône).

Twinning and special crystallizations

No twin known for this mineral species.

Fakes and treatments

No fake identify for this mineral species.


Hardness : 3.5
Density : 3.02
Fracture : Irregular
Trace : White

TP : Translucent
RI : 1.644 to 1.668
Birefringence : 0.017 to 0.020
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Insoluble

Magnetism : None
Radioactivity : None