Bayerite

bayerite

gibbsite

nordstrandite

diaspore

Images
Formula: Al(OH)3
Hydroxide, paramorph of gibbsite, nordstrandite and doyleite

Specific gravity: 2.53
Streak: White
Colour: Colourless
Environments

Hydrothermal environments

Bayerite occurs in bauxite and as weathered crusts on amphiboles and pyroxenes (Webmin).

Localities

At the type locality, the Hatrurim Formation, Middle East, investigators used X-ray diffraction to identify the bayerite, which occurs with calcite and gypsum in veinlets cutting sedimentary rocks of late Cretaceous age. The rocks are composed of calcite and spurrite. The veinlets also contain vaterite, portlandite, tobermorite group minerals, thaumasite and ettringite. Several of these minerals connote genesis at a very high pH (strongly alkaline), and this agrees with the conditions under which pure bayerite is formed synthetically (pH>12). (AM 55.43, Mindat). It is probably precipitated from high-alumina gels on carbonates at pH>5.8 (HOM).

At the Listvennoye deposit, Enisei Range, Krasnoyarsk Territory, Eastern-Siberian Region, Russia, bayerite occurs as weathered crusts on amphiboles and pyroxenes (HOM). Associated minerals include gibbsite, diaspore and possibly nordstrandite (AM 55.43).

Alteration

Synthesis experiments in the alumina-water system at room temperature indicate that the gibbsite polymorph precipitates slowly from solutions whose pH is below the point of minimum solubility (pH 5.8), ie acid, and the bayerite polymorph precipitates rapidly from solutions whose pH is above 5.8. Nordstrandite, the third polymorph of aluminum hydroxide, forms from bayerite during aging at intermediate to high pH values (alkaline to very alkaline). In solutions of intermediate pH, both gibbsite and bayerite form, but with aging, early-formed gibbsite disappears as more bayerite forms. During aging, the pH's of the mother liquors decrease if gibbsite precipitates and increase if bayerite precipitates (AM 55.43).

Back to Minerals