Böhmite - Encyclopedia
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 in the World
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