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°
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.