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China clay

Kaolinite
KaoliniteUSGOV.jpg
General
Category Phyllosilicates
Kaolinite-serpentine group
Formula
(repeating unit)
Al2Si2O5(OH)4
Strunz classification 9.ED.05
Crystal system Triclinic
Crystal class Pedial (1)
(same H-M symbol)
Space group P1
Unit cell a = 5.13 Å, b = 8.89 Å
c = 7.25 Å; α = 90°
β = 104.5°, γ = 89.8°; Z = 2
Identification
Color White, sometimes red, blue or brown tints from impurities
Crystal habit Rarely as crystals, thin plates or stacked, More commonly as microscopic pseudohexagonal plates and clusters of plates, aggregated into compact, claylike masses
Cleavage Perfect on {001}
Tenacity Flexible but inelastic
Mohs scale hardness 2–2.5
Luster Pearly to dull earthy
Streak White
Specific gravity 2.16–2.68
Optical properties Biaxial (–)
Refractive index nα = 1.553–1.565,
nβ = 1.559–1.569,
nγ = 1.569–1.570
2V angle Measured: 24° to 50°, Calculated: 44°
References
Kaolinite
Traditional Chinese 高嶺石
Simplified Chinese 高岭石
Literal meaning "Gaoling stone"

Kaolinite /ˈkəlˌnt/ is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica (SiO4) linked through oxygen atoms to one octahedral sheet of alumina (AlO6) octahedra. Rocks that are rich in kaolinite are known as kaolin /ˈkəln/ or china clay.

The name "kaolin" is derived from "Gaoling" (Chinese: 高嶺; pinyin: Gāolǐng; literally: "High Ridge"), a Chinese village near Jingdezhen in southeastern China's Jiangxi Province. The name entered English in 1727 from the French version of the word: kaolin, following Francois Xavier d'Entrecolles's reports from Jingdezhen.


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