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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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 % H 
Oxygen 57.57 % O 
 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
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allophane
danh từ (khoáng chất) Alophan
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ALLOFANE

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