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° |
References |
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.