Allophane is an
amorphoushydrous 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 diffractionpattern. It was first described in 1816 in Gräfenthal, Thuringia, Germany. Allophane is a weatheringor hydrothermalalteration product of feldspars and other primary minerals and has a composition similar to kaolinite. A coppercontaining variety "cupro-allophane" has been reported.
It forms waxy botryoidal to crusty masses with color varying from white through green, blue, yellow, to brown. It has a
Mohs hardnessof 3 and a specific gravityof 1.0.
It was named from the Greek "allos" - "other" and "phanos" - "to appear", as it gave a deceptive reaction in the blowpipe flame in old mineralogical testing.
* [http://webmineral.com/data/Allophane.shtml Webmineral data]
* [http://www.mindat.org/min-139.html Mindat]
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