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Kaolinite facts for kids

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Kaolinite from Twiggs County in Georgia in USA.jpg
Category Phyllosilicates
Kaolinite-serpentine group
(repeating unit)
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
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.
Kaolinite strcutural model VA
Ball-and-stick model of Kaolinite; Oxygen atoms do the linking between silicate and alumina sheets

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