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Kaolinite Facts for Kids. Kiddle Encyclopedia.
| Kaolinite | |
|---|---|
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| 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.
- 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.