| Kaolinite | |
|---|---|
 | |
| General | |
| Category | Phyllosilicates Kaolinite-serpentine group |
| Formula (repeating unit) | Al2Si2O5(OH)4, or in oxide notation: Al2O3·2SiO2·2H2O |
| IMA symbol | Kln[1] |
| Strunz classification | 9.ED.05 |
| Crystal system | Triclinic |
| Crystal class | Pedial (1) (same H-M symbol) |
| 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 to cream, sometimes red, blue or brown tints from impurities and pale-yellow; also often stained various hues, tans and browns being common. |
| Crystal habit | Rarely as crystals, thin plates or stacked. More commonly as microscopic pseudohexagonal plates and clusters of plates, aggregated into compact, claylike masses. |
| 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 | [2][3][4] |
Kaolinite (/ˈkeɪ.ələˌnaɪt, -lɪ-/ KAY-ə-lə-nyte, -lih-; also called kaolin)[5][6][7] is a clay mineral, with the chemical composition: Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica (SiO4) linked through oxygen atoms to one octahedral sheet of alumina (AlO6).[8]
Kaolinite is a soft, earthy, usually white, mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. It has a low shrink–swell capacity and a low cation-exchange capacity (1–15 meq/100 g).
Rocks that are rich in kaolinite, and halloysite, are known as kaolin (/ˈkeɪ.əlɪn/) or china clay.[9] In many parts of the world kaolin is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lower concentrations of iron oxide yield the white, yellow, or light orange colors of kaolin. Alternating lighter and darker layers are sometimes found, as at Providence Canyon State Park in Georgia, United States.
Kaolin is an important raw material in many industries and applications. Commercial grades of kaolin are supplied and transported as powder, lumps, semi-dried noodle or slurry. Global production of kaolin in 2021 was estimated to be 45 million tonnes,[10] with a total market value of $US4.24 billion.[11]
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Kaolinite, Mindat.org, retrieved 5 August 2009
- ^ Kaolinite Mineral Data, WebMineral.com, retrieved 5 August 2009
- ^ Anthony JW, Bideaux RA, Bladh KW, et al., eds. (1995). "Kaolinite" (PDF). Handbook of Mineralogy: Silica, silicates. Tucson, Ariz.: Mineral Data Publishing. ISBN 9780962209734. OCLC 928816381.
- ^ "kaolinite". Dictionary.com Unabridged (Online). n.d.
- ^ "kaolinite". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 25 January 2021.
- ^ "kaolinite". The American Heritage Dictionary of the English Language (5th ed.). HarperCollins.
- ^ Deer, Howie & Zussman (1992).
- ^ Pohl WL (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 9781444336627.
- ^ 'U.S. Geological Survey, Mineral Commodity Summaries, January 2022' USGS, 2022.
- ^ 'Kaolin Market Size, Share & Trends Analysis Report By Application, By Region And Segment Forecasts, 2022 - 2030. Grand View Research, 2022