Allophane

ALLOPHANE (from the Greek word "allophanes", appearing as other; is similar to the certain minerals of the copper, as which it has been mistakenly recognized * EN: allophane; DE: Allophan; FR: allophane; ES: alyfana; RU: аллофан) is the mineral, the aqueous aluminium silicate of the varying composition; mA12O3 • nSiO2 • pH2O. It often contains Fe2O3 (up to 0.8% in the ferroallofane), MgO, CaO, K2O, Na2O, CuO, ZnO, P2O5, CO2, SO3 admixtures. It is similar by its composition to the halloysite, to which it often transitions during the change and de-crystallization.

It is amorphous. It forms the glass-like transparent or translucent, less often powdery masses, flowstones, crusts. The colour is bluish, greenish, yellowish, sometimes deep-green, brown; there may be also found the white and colourless allophane. The hardness is about 3.0 (in distinction from the transparent opal). It is very brittle. The density is 1870±20 kilograms per cubic metre.

It is supergene. It is formed in the zones of the oxidation of the ore deposits in the crusts of the weathering.