Pyrophyllite
A soft phyllosilicate used in carving and industrial applications.
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Pyrophyllite is a phyllosilicate mineral with the composition Al2Si4O10(OH)2. It appears in two habits: crystalline folia and compact masses, with distinct crystals unknown. The folia exhibit a pearly luster, are flexible but not elastic, and exfoliate upon heating, while both varieties are very soft and greasy to the touch.
Occurrence
Pyrophyllite is found in phyllite and schistose rocks, often as an alteration product of kyanite, and also in hydrothermal deposits. Associated minerals include kyanite, andalusite, topaz, mica, and quartz. Notable deposits include a 21-million-ton high-grade deposit at Manuels, Newfoundland and Labrador, Canada; pale green foliated masses at Beresovsk near Yekaterinburg, Russia; and locations in Switzerland, Sweden, Belgium, Brazil, Japan, and several US states. In South Africa, major deposits near Ottosdal yield blocks marketed as "Wonderstone" for carving.
Uses
The compact variety serves as slate pencils and tailors' chalk, and is carved by the Chinese into small images and ornaments. Under the terms agalmatolite and pagodite, it includes other soft minerals like steatite and pinite. Pyrophyllite is machineable, thermally stable, and added to clay to reduce thermal expansion during firing. It is also used in insecticides, brickmaking, and as a gasket material and pressure-transmitting medium in high-pressure experiments.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Pyrophyllite (CC BY-SA 4.0).
- Word definitions: the , each quoted from its Wikipedia article.
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