Montmorillonite
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Montmorillonite is a very soft phyllosilicate mineral that typically forms in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a central octahedral sheet. The particles are plate-shaped with an average diameter of approximately 1 micrometre. The particle thickness is extremely small (~ 1 nm).
It is the main constituent of the volcanic ash weathering product, bentonite. Montmorillonite's water content is variable and it increases greatly in volume when it absorbs water. Chemically it is hydrated sodium calcium aluminium magnesium silicate hydroxide (Na,Ca)x(Al,Mg)2(Si4O10)(OH)2·nH2O. Potassium, iron, and other cations are common substitutes, the exact ratio of cations varies with source.
It is used in the oil drilling industry as a component of drilling mud, making the water slurry viscous which helps in keeping the drill head cool and removing drill debris. It is also used as a soil additive to hold soil water in drought prone soils, to the construction of earthen dams and levees and to prevent the leakage of fluids. It is also used as a component of foundry sand and as a desiccant to remove moisture from air and gases.
Similar to other clays, montmorillonite swells with the addition of water. However, some montmorillonites expand considerably more than other clays due to water penetrating the interlayer molecular spaces and concomitant adsorption. The amount of expansion is due largely to the type of exchangeable cation contained in the sample. The presence of sodium as the predominant exchangeable cation can result in the clay swelling to several times its original volume. Hence, sodium montmorillonite has come to be used as the major constituent in non-explosive agents for splitting rock in natural stone quarries in order to limit the amount of waste, or for the demolition of concrete structures where the use of explosive charges is unacceptable.
Montmorillonite has been used in cosmetics and has reputed therapeutic effects. Indeed over 200 cultures have used the clay for medicinal purposes including the Ancient Egyptians, the Essenes and the pre-Aztec Amargosians, and other natives of Mexico, South America and North America.
Montmorillonite is also used in animal feeds as an anti-caking agent. Current research indicates that montmorillonite or bentonite has the ability to bind mycotoxins in the digestive system of animals as well as several bacteria in-vitro.
Montmorillonite was discovered in 1847 in Montmorillon in the Vienne prefecture of France, but is found in many locations world wide and known by other names. Other modern discoveries include about 1830 by the French-Canadian fur trapper Emile Pascal atop the 8600 feet high Big Horn Mountains in Wyoming, USA and as bentonite in about 1890 and named by an American geologist for the one time Fort Benton (on the Fort Benton Formation geological stratum) in the eastern Wyoming Rock Creek area. Native Americans have referred to the therapeutic clay as Ee-Wah-Kee.
[edit] See also
[edit] References
- Papke, Keith G. Montmorillonite, Bentonite and Fuller’s Earth Deposits in Nevada, Nevada Bureau of Mines Bulletin 76, Mackay School of Mines, University of Nevada-Reno, 1970.
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