"Kaolin" redirects here. For the Sailor Moon character, see Death Busters#Kaolinite.
| Kaolinite |
|
| General |
| Category |
Silicate mineral |
Formula
(repeating unit) |
Al2Si2O5(OH)4 |
| 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 platy 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 |
[1][2][3] |
Kaolinite is a clay mineral, part of the group of industrial minerals, 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 octahedra.[4] Rocks that are rich in kaolinite are known as kaolin or china clay.[5]
The name is derived from Kao-ling (Chinese: 高岭/高嶺; pinyin: Gaoling), a village near Jingdezhen, Jiangxi province, China.[6] The name entered English in 1727 from the French version of the word: "kaolin", following Francois Xavier d'Entrecolles's reports from Jingdezhen.[7] In Africa, kaolin is sometimes known as kalaba (in Gabon[8] and Cameroon[9]), calaba, and calabachop (in Equatorial Guinea).
Kaolinite has a low shrink-swell capacity and a low cation exchange capacity (1-15 meq/100g). It is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay), 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, USA. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.
|
Contents
- 1 Chemistry
- 1.1 Notation
- 1.2 Structural transformations
- 2 Occurrence
- 2.1 Predominance in tropical soils
- 3 Uses
- 4 See also
- 5 References
- 6 External links
|
Chemistry
Notation
While the most common chemical notation for kaolin is Al2Si2O5(OH)4, in ceramics applications the formula is typically written in terms of oxides, thus the formula for kaolinite is Al2O3·2SiO2·2H2O. Cement chemist notation even more terse: AS2H2, with the oxides represented as A = Al2O3, S = SiO2, H = H2O.
Structural transformations
Kaolinite group clays undergo a series of phase transformations upon thermal treatment in air at atmospheric pressure. Endothermic dehydroxylation (or alternatively, dehydration) begins at 550–600 °C to produce disordered metakaolin, Al2Si2O7, but continuous hydroxyl loss (-OH) is observed up to 900 °C and has been attributed to gradual oxolation of the metakaolin.[10] Because of historic disagreement concerning the nature of the metakaolin phase, extensive research has led to general consensus that metakaolin is not a simple mixture of amorphous silica (SiO2) and alumina (Al2O3), but rather a complex amorphous structure that retains some longer-range order (but not strictly crystalline) due to stacking of its hexagonal layers.[10]
- 2 Al2Si2O5(OH)4 → 2 Al2Si2O7 + 4 H2O.
Further heating to 925–950 °C converts metakaolin to an aluminium-silicon spinel, Si3Al4O12, which is sometimes also referred to as a gamma-alumina type structure:
- 2 Al2Si2O7 → Si3Al4O12 + SiO2.
Upon calcination to ~1050 °C, the spinel phase (Si3Al4O12) nucleates and transforms to mullite, 3 Al2O3 · 2 SiO2, and highly crystalline cristobalite, SiO2:
- 3 Si3Al4O12 → 2 Si2Al6O13 + 5 SiO2.
Occurrence
A kaolin mine in Ruse Province, Bulgaria
Kaolinite is one of the most common minerals; it is mined, as kaolin, in Brazil, Bulgaria, France, United Kingdom, Iran, Germany, India, Australia, Korea, the People's Republic of China, the Czech Republic and the United States.[1]
Predominance in tropical soils
Kaolinite clay occurs in abundance in soils that have formed from the chemical weathering of rocks in hot, moist climates—for example in tropical rainforest areas. Comparing soils along a gradient towards progressively cooler or drier climates, the proportion of kaolinite decreases, while the proportion of other clay minerals such as illite (in cooler climates) or smectite (in drier climates) increases. Such climatically-related differences in clay mineral content are often used to infer changes in climates in the geological past, where ancient soils have been buried and preserved.
In the Institut National pour l'Etude Agronomique au Congo Belge (INEAC) classification system, soils in which the clay fraction is predominantly kaolinite are called kaolisol (from kaolin and soil).[11]
Uses
The largest use is in the production of paper, including ensuring the gloss on some grades of paper.
In April 2008, the US Naval Medical Research Institute announced the successful use of a kaolinite-derived aluminosilicate nanoparticle infusion in traditional gauze, known commercially as QuikClot Combat Gauze.[12]
Kaolin is or was also used:
- in ceramics. It is generally the main component in porcelain.
- in toothpaste
- as a light diffusing material in white incandescent light bulbs
- in cosmetics
- as paint to extend titanium dioxide (TiO2) and modify gloss levels;
- for its semi-reinforcing properties in rubber
- in adhesives to modify rheology.[13]
- the production of common smoking pipes in Europe and Asia
- in organic farming, as a spray applied to crops to deter insect damage, and in the case of apples, to prevent sun scald.
- as whitewash in traditional stone masonry homes in Nepal. The most common method is to paint the upper part with white Kaolin clay and the middle with red clay. The red clay may extend to the bottom, or the bottom may be painted black.
- as a filler in Edison Diamond Discs.[14]
- as an indicator in radiological dating since Kaolinite can contain very small traces of uranium and thorium.
- to soothe an upset stomach, similar to the way parrots (and later, humans) in South America originally used it.[15] More recently, industrially-produced kaolinite preparations were formerly common for treatment of diarrhea; the most common of these was Kaopectate, which abandoned the use of kaolin in favor of attapulgite and then (in the United States) bismuth subsalicylate (the active ingredient in Pepto-Bismol).
- for facial masks or soap[16]
According to the American National Precast Concrete Association metakaolin is a supplementary cementitious material (SCM). When added to a concrete mix, metakaolin accelerates the hydration of Portland cement.
Geophagy
Kaolin is eaten for pleasure or to suppress hunger,[9] a practice known as geophagy. Consumption is greater among women, especially during pregnancy.[17] This practice has also been observed within a small population of African-American women in the Southern United States, especially Georgia.[18] There, the kaolin is called white dirt, chalk or white clay.[18]
See also
- List of English words of Chinese origin
- Silicate minerals
- Dickite
- Geology of Cornwall
- Halloysite
- Nacrite
- Medicinal clay
- Porcelain
- Clay pit
- Kaolin Deposits of Charentes Basin, France
References
- Notes
- ^ a b "Kaolinite mineral information and data". MinDat.org. http://www.mindat.org/min-2156.html. Retrieved 2009-08-05.
- ^ "Kaolinite Mineral Data". WebMineral.com. http://www.webmineral.com/data/Kaolinite.shtml. Retrieved 2009-08-05.
- ^ Kaolinite in the Handbook of Mineralogy
- ^ 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.
- ^ 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. pp. 331. ISBN 978-1-4443-3662-7. http://books.google.com/books?id=VxErg26BKx4C.
- ^ Schroeder, Paul (2003-12-12). "Kaolin". New Georgia Encyclopedia. http://www.georgiaencyclopedia.org/nge/Article.jsp?id=h-1178. Retrieved 2008-08-01.
- ^ Harper, Douglas. "kaolin". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=kaolin.
- ^ 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.
- ^ a b Franklin Kamtche. "Balengou : autour des mines." (Balengou: around the mines) Le Jour. 12 January 2010. (French)
- ^ a b Bellotto, M., Gualtieri, A., Artioli, G., and Clark, S.M. (1995). "Kinetic study of the kaolinite-mullite reaction sequence. Part I: kaolinite dehydroxylation". Phys. Chem. Minerals 22 (4): 207–214. Bibcode 1995PCM....22..207B. doi:10.1007/BF00202253.
- ^ Young, Anthony (1980). Tropical soils and soil survey. Cambridge Geographical Studies. 9. CUP Archive. p. 132. ISBN 0-521-29768-0.
- ^ Rowe, Aaron (24 April 2008). "Nanoparticles help gauze stop gushing wounds". Wired.com. http://www.wired.com/medtech/health/news/2008/04/blood_clotting. Retrieved 2009-08-05.
- ^ Ciullo, Peter A. (1996). Industrial minerals and their uses: a handbook and formulary. William Andrew. pp. 41-43. ISBN 978-0-8155-1408-4. http://books.google.com/books?id=WiEs4oe2ziUC&pg=PA43&lpg=PA43&dq=kaolin+uses+paint+rubber+adhesives&source=bl&ots=D2ix0KuiXt&sig=x1VgDCzGTFiDVo4aBrNu3sDGNgM&hl=en&sa=X&ei=DCtkT6uuN-yPsAK7rey3Dw&ved=0CEwQ6AEwBjgU#v=onepage&q=kaolin%20uses%20paint%20rubber%20adhesives&f=false.
- ^ Edison Diamond Disc information
- ^ Diamond, Jared M. (1999). "Evolutionary biology: Dirty eating for healthy living". Nature (Nature) 400 (6740): 120–121. Bibcode 1999Natur.400..120D. doi:10.1038/22014. PMID 10408435. http://cogweb.ucla.edu/Abstracts/Diamond_99.html.
- ^ "Secrets et rituels des femmes camerounaises." (Secrets and rituals of women in Cameroon) at Gennybeauté.com (French)
- ^ Gerald N. Callahan. "Eating Dirt." Emerging Infectious Diseases. 9.8 (August 2003).
- ^ a b R. Kevin Grigsby "Clay Eating." New Georgia Encyclopedia. 3 February 2004.
- Bibliography
- Deer, W.A., Howie, R.A., and Zussman, J. (1992) An introduction to the rock-forming minerals (2nd ed.). Harlow: Longman ISBN 0-582-30094-0.
- Hurlbut, Cornelius S., Klein, Cornelis (1985) Manual of mineralogy – after J. D. Dana, 20th ed., Wiley, pp. 428–429, ISBN 0-471-80580-7.
- Breck, D.W. (1984) Zeolite molecular sieves, Robert E., Brieger Publishing Company: Malabar, FL, pp. 314–315, ISBN 0-89874-648-5.
- The mineral kaolinite – Mineral galleries
- MSDS: Incandescent Light Bulb – GE
External links
|
Phyllosilicates
|
|
| Serpentine group |
- Antigorite
- Chrysotile
- Lizardite
- Népouite
|
|
| Clay mineral group |
- Chlorite1
- Dickite
- Halloysite
- Illite
- Ilmenite
- Kaolinite
- Montmorillonite
- Nacrite
- Nontronite
- Palygorskite
- Saponite
- Sepiolite
- Serpentine1
- Talc
|
|
| Mica group |
- Biotite
- Glauconite
- Lepidolite
- Margarite
- Muscovite
- Phlogopite
|
|
| Chlorite group |
|
|
|
1. Serpentine and Chlorite are sometimes considered clay minerals
|
|
|
Clay minerals
|
|
- Allophane
- Chlorite
- Dickite
- Halloysite
- Hectorite
- Illite
- Ilmenite
- Imogolite
- Kaolinite
- Montmorillonite
- Nacrite
- Nontronite
- Palygorskite
- Saponite
- Sepiolite
|
|
