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Allophane

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Allophane
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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Allophane

General Information:
 Chemical Formula:
Al2O3·(SiO2)1·3-2·((H2O))2·5-3
 Composition:
(Molecular Weight = 225.11 gm)
Aluminum 23.97 % Al
Silicon 16.22 % Si
Hydrogen 2.24 % 
Oxygen 57.57 % 
 Empirical Formula:
(Al2O3)(SiO2)1.3·2.5(H2O)
 Name Origin:
From the Greek allos - "other" and phanos - "to appear."
Physical Properties:
 Cleavage:
None
 Color:
white, green, blue, yellow, or brown.
 Density:
1.9
 Diaphaniety:
Translucent
 Habits:
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).
 Hardness:
3 - Calcite
 Luminescence:
None.
 Luster:
Waxy
 Streak:
white
More details...

Free English-Vietnamese Dictionary

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allophane
allophane
  • danh từ
    • (khoáng chất) Alophan

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    Dizionario inglese-italiano 1.0.012

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    ALLOPHANE
    ALLOFANE

    Glosarium Pusat Bahasa Depdiknas Indonesia

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    allophane
    B: (Kimia) alofan

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