Kaolinite

Kaolinite
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"
Transcriptions Standard Mandarin Hanyu Pinyin Gāolǐng shí Wade–Giles Kao1-ling3 shih2 IPA [káu.lìŋ ʂɨ̌]

Transcriptions
Standard Mandarin
Hanyu Pinyin	Gāolǐng shí
Wade–Giles	Kao1-ling3 shih2
IPA	[káu.lìŋ ʂɨ̌]

Kaolinite /ˈkeɪəlᵻˌnaɪt/ 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 /ˈkeɪəlᵻn/ 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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