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Halloysite
Aluminosilicate clay mineral / From Wikipedia, the free encyclopedia
Halloysite is an aluminosilicate clay mineral with the empirical formula Al2Si2O5(OH)4. Its main constituents are oxygen (55.78%), silicon (21.76%), aluminium (20.90%), and hydrogen (1.56%). It is a member of the kaolinite group. Halloysite typically forms by hydrothermal alteration of alumino-silicate minerals.[4] It can occur intermixed with dickite, kaolinite, montmorillonite and other clay minerals. X-ray diffraction studies are required for positive identification. It was first described in 1826, and subsequently named after, the Belgian geologist Omalius d'Halloy.
Quick Facts General, Category ...
Halloysite | |
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General | |
Category | Phyllosilicates Kaolinite-serpentine group |
Formula (repeating unit) | Al2Si2O5(OH)4 |
Strunz classification | 9.ED.10 |
Crystal system | Monoclinic |
Crystal class | Domatic (m) (same H-M symbol) |
Space group | Cc |
Unit cell | a = 5.14, b = 8.9, c = 7.214 [Å]; β = 99.7°; Z = 1 |
Identification | |
Color | White; grey, green, blue, yellow, red from included impurities. |
Crystal habit | Spherical clusters, massive |
Cleavage | Probable on {001} |
Fracture | Conchoidal |
Mohs scale hardness | 2–2.5 |
Luster | Pearly, waxy, or dull |
Diaphaneity | Semitransparent |
Specific gravity | 2–2.65 |
Optical properties | Biaxial |
Refractive index | nα = 1.553–1.565 nβ = 1.559–1.569 nγ = 1.560–1.570 |
Birefringence | δ = 0.007 |
References | [1][2][3] |
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