layered aluminosilicate 1:1 clay mineral

Kaolinite or Kaolin is a clay mineral. It is in a group with the chemical composition Al2Si2O5(OH)4.[4] It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina.[5] Rocks that are rich in kaolinite are known as kaolin or china clay.[6]

Kaolinite-serpentine group
(repeating unit)
Strunz classification09.ED.05
Crystal symmetryTriclinic pedial
H-M symbol: (1)
Space group: P1
Unit cella = 5.13 Å, b = 8.89 Å, c = 7.25 Å; α = 90°, β = 104.5°, γ = 89.8°; Z = 2
ColorWhite, sometimes red, blue or brown tints from impurities
Crystal habitRarely as crystals, thin plates or stacked, More commonly as microscopic pseudohexagonal plates and clusters of plates, aggregated into compact, claylike masses
Crystal systemTriclinic
CleavagePerfect on {001}
TenacityFlexible but inelastic
Mohs scale hardness2–2.5
LusterPearly to dull earthy
Specific gravity2.16–2.68
Optical propertiesBiaxial (–)
Refractive indexnα = 1.553–1.565,
nβ = 1.559–1.569,
nγ = 1.569–1.570
2V angleMeasured: 24° to 50°, Calculated: 44°

The name is after Kao-Ling, a village near Jingdezhen, Jiangxi province, China.[7] 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.[8][9]

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.[10]

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

References change

  1. "Kaolinite mineral information and data". MinDat.org. Retrieved 2009-08-05.
  2. "Kaolinite Mineral Data". WebMineral.com. Retrieved 2009-08-05.
  3. Kaolinite in the Handbook of Mineralogy
  4. "kaolinite facts, information, pictures | Encyclopedia.com articles about kaolinite". www.encyclopedia.com. Retrieved 2017-10-19.
  5. Deer, W.A.; Howie, R.A.; Zussman, J. (1992). An introduction to the rock-forming minerals (2 ed.). Harlow: Longman. ISBN 0-582-30094-0.
  6. Pohl, Walter L. (2011). Economic geology: principles and practice : metals, minerals, coal and hydrocarbons – introduction to formation and sustainable exploitation of mineral deposits. Chichester, West Sussex: Wiley-Blackwell. p. 331. ISBN 978-1-4443-3662-7.
  7. Schroeder, Paul (2003-12-12). "Kaolin". New Georgia Encyclopedia. Archived from the original on 2012-10-11. Retrieved 2008-08-01.
  8. Karine Boucher, Suzanne Lafage. "Le lexique français du Gabon: K." Le Français en Afrique: Revue du Réseau des Observatoires du Français Contemporain en Afrique. 2000.
  9. Franklin Kamtche. "Balengou : autour des mines." Archived 2012-03-04 at the Wayback Machine (Balengou: around the mines) Le Jour. 12 January 2010. (in French)
  10. "Kaolinite | Minerals Education Coalition". Minerals Education Coalition. Retrieved 2017-10-19.