Kaolinite facts for kids

Quick facts for kids Kaolinite
General
Category	Phyllosilicates Kaolinite-serpentine group
Formula (repeating unit)	Al2Si2O5(OH)4
Strunz classification	09.ED.05
Crystal symmetry	Triclinic pedial H-M symbol: (1) 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
Crystal system	Triclinic
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°

Kaolinite or Kaolin is a clay mineral. It is in a group with the chemical composition Al₂Si₂O₅(OH)₄. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina. Rocks that are rich in kaolinite are known as kaolin or china clay.

The name is after Kao-Ling, a village near Jingdezhen, Jiangxi province, China. The name entered English in 1727 from the French kaolin, used in a Jesuit priest's reports from Jingdezhen. In Africa, kaolin is sometimes known as kalaba or calaba.

Kaolinite is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay). It is produced by the chemical weathering of aluminium silicate minerals like feldspar. In many parts of the world, it is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow or light orange colors. Alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, United States. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.

Kaolinite is said to have a low shrink-swell capacity and a low cation-exchange capacity, which makes it ideal for various industrial applications.

• Kaolin is a main ingredient in making porcelain. Its main industrial use now is in manufacturing paper, especially whiter high-gloss papers. It is also used in toothpastes, make-up and paint.

Ball-and-stick model of Kaolinite; Oxygen atoms do the linking between silicate and alumina sheets

Images for kids

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  Kaolinite structure, showing the interlayer hydrogen bonds

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  Georgia red clay

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  View of the structure of the tetrahedral (T) sheet of kaolinite

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  View of the structure of the octahedral (O) sheet of kaolinite

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  Kaolinite crystal structure looking along the layers

See also

In Spanish: Caolinita para niños