Allophane

Allophane is an amorphous hydrous aluminium silicate clay mineral. Its chemical formula is Al2O3·(SiO2)1.3-2·2.5-3(H2O). Although it has a variable composition and although generally amorphous in structure, it has long been recognized as a mineral and can be identified by its distinctive X-ray diffraction pattern. It was first described in 1816 in Gräfenthal, Thuringia, Germany. Allophane is a weathering or hydrothermal alteration product of feldspars and other primary minerals and has a composition similar to kaolinite. A copper containing variety cupro-allophane has been reported.
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Du grec allos, autre et phaneîn, paraître.
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L'allofane è un minerale. Deriva il suo nome dal greco allos - altro e fanos apparire, in quanto al saggio secco (arrostimento su fiamma) dava risultati ingannatori.
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Het mineraal allofaan is een gehydrateerd-aluminium-silicaat met de chemische formule (Al2O3)(SiO2)1.3·2.5(H2O). Het mineraal behoort tot de fylosilicaten.
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ALLOFANE