White, pale blue to sky-blue, green, brown, yellow
Crystal habit
Crusts and masses
Cleavage
None
Fracture
Conchoidal
Tenacity
Brittle
Mohs scale hardness
3
Luster
Waxy to earthy
Streak
White
Diaphaneity
Transparent, translucent
Specific gravity
2.8
Allophane is an amorphous to poorly crystalline hydrous aluminium silicate clay mineraloid. Its chemical formula is Al2O3·(SiO2)1.3-2·(2.5-3)H2O. Since it has short-range atomic order, it is a mineraloid, rather than a mineral, and can be identified by its distinctive infrared spectrum and its X-ray diffraction pattern. It was first described in 1816 in Gräfenthal, Thuringia, Germany. Allophane is a weathering or hydrothermal alteration product of volcanic glass and feldspars and sometimes has a composition similar to kaolinite but generally has a molar ratio of Al:Si = 2. It typically forms under mildly acidic to neutral pH (5–7). Its structure has been debated, but it is similar to clay minerals and is composed of curved alumina octahedral and silica tetrahedral layers.[2] Transmission electron micrographs show that it is generally made up of aggregates of hollow spherules ~3–5 nm in diameter. Allophane can alter to form halloysite under resilicating aqueous conditions and can alter to form gibbsite under desilicating conditions. A copper-containing 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 hardness of 3 and a specific gravity of 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.
Allophane is an amorphous to poorly crystalline hydrous aluminium silicate clay mineraloid. Its chemical formula is Al2O3·(SiO2)1.3-2·(2.5-3)H2O. Since...
Allophanes is a genus of beetles in the family Carabidae, containing the following species: Allophanes auripennis (Chaudoir, 1877) Allophanes drescheri...
high proportions of glass and amorphous colloidal materials, including allophane, imogolite and ferrihydrite. In the World Reference Base for Soil Resources...
U.S. ice-free land. Andisols: Form from volcanic ejecta, dominated by allophane or Al-humic complexes; Must have andic soil properties: high in poorly...
basic or the climate is dry, amorphous colloidal materials, including allophane and imogolite develop, and the Andosols are given the Silandic qualifier...
in length at the El Dragon Mine, Potosi, Bolivia in association with allophane, chalcomenite, clinochalcomenite and barite. Wikimedia Commons has media...
significance of alternating wet and dry conditions on the transition of allophane into kaolinite has been stressed by Tamura and Jackson (1953). The role...
alluvium. Trumaos are characterized by containing the following minerals: allophane, imogolite plus a series of paracrystalline and non-crystalline clays...
Global Information