Dickite | |
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General | |
Category | Phyllosilicates Kaolinite-serpentine group |
Formula (repeating unit) | Al2Si2O5(OH)4 |
IMA symbol | Dck[1] |
Strunz classification | 9.ED.05 |
Dana classification | 71.01.01.01 |
Crystal system | Monoclinic |
Crystal class | Domatic (m) (same H-M symbol) |
Space group | Cc |
Unit cell | a = 5.150, b = 8.940 c = 14.424 [Å]; β = 96.8°; Z = 4 |
Identification | |
Color | White, with coloration from impurities |
Crystal habit | Pseudohexagonal crystals, aggregates of platelets and compact massive |
Cleavage | Perfect on {001} |
Tenacity | Flexible but inelastic |
Mohs scale hardness | 1.5–2 |
Luster | Satiny to pearly |
Streak | White |
Diaphaneity | Transparent |
Specific gravity | 2.6 |
Optical properties | Biaxial (+) |
Refractive index | nα = 1.561 – 1.564 nβ = 1.561 – 1.566 nγ = 1.566 – 1.570 |
Birefringence | δ = 0.005 – 0.006 |
2V angle | Measured: 50° to 80° |
References | [2][3][4][5][6][7][8][9][10][11][12] |
Dickite (Al2Si2O5(OH)4) is a phyllosilicate clay mineral named after the metallurgical chemist Allan Brugh Dick, who first described it. It is chemically composed of 20.90% aluminium, 21.76% silicon, 1.56% hydrogen and 55.78% oxygen. It has the same composition as kaolinite, nacrite, and halloysite, but with a different crystal structure (polymorph). Dickite sometimes contains impurities such as titanium, iron, magnesium, calcium, sodium and potassium.[3]
Dickite occurs with other clays and requires x-ray diffraction for its positive identification. Dickite is an important alteration indicator[clarification needed] in hydrothermal systems as well as occurring in soils and shales.
Dickite's type location is in Pant-y-Gaseg, Amlwch, Isle of Anglesey, Wales, United Kingdom, where it was first described in 1888.[3] Dickite appears in locations with similar qualities and is found in China, Jamaica, France, Germany, United Kingdom, United States, Italy, Belgium and Canada.[12]
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