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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, ThuringiaGermany. 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. 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.

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Mineralogy Database Dictionary

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General Information:
 Chemical Formula:
(Molecular Weight = 225.11 gm)
Aluminum 23.97 % Al
Silicon 16.22 % Si
Hydrogen 2.24 % 
Oxygen 57.57 % 
 Empirical Formula:
 Name Origin:
From the Greek allos - "other" and phanos - "to appear."
Physical Properties:
white, green, blue, yellow, or brown.
Encrustations - Forms crust-like aggregates on matrix., Stalactitic - Shaped like pendant columns as stalactites or stalagmites (e.g. calcite)., Botryoidal - "Grape-like" rounded form s (e.g.. malachite).
3 - Calcite
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Free English-Vietnamese Dictionary

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  • danh từ
    • (khoáng chất) Alophan

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    Dizionario inglese-italiano 1.0.012

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    Glosarium Pusat Bahasa Depdiknas Indonesia

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    B: (Kimia) alofan

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