talc - dark green soapstone/pyrophyllite talc - teaching student specimens - UNIT OF 5 SPECIMENS
This is a complex talcose mineral, called pyrophyllite at the mine and is a mixture of amesite and talc. It serves as a student example of soapstone talc.
Pyrophyllite and talc are two minerals with similar physical properties. Both are very soft, with talc the softest at 1 on the Mohs hardness scale. Pyrophyllite’s hardness is 1 to 2. Both can be easily cut and both have perfect cleavage in one direction, which allows thin sheets of these minerals to slide over one another, giving them a greasy feel. Both form from the metamorphism of dolomite.
Pyrophyllite is a hydrous aluminum silicate and is used in many products as an alternative to talc which is a hydrous magnesium silicate.
Pyrophyllite comes from the Greek words pyro (fire) and phyllon (leaf), since it exfoliates and swells up to many times its original volume when heated. It was named by German chemist Hans Rudolf Hermann (1805-1879) in 1829 in a note: Zerlegung des Pyrophyllits, eines neuen Minerals in Annalen der Physik und Chemie: 15: 592-592. See photos for original description and translation. Click to select, click again to enlarge.
Like talc, ground pyrophyllite is used in the manufacture of ceramics, cosmetics, paint, paper, fiberglass, rubber and heat-resistant refractories. We previously had this mineral identified as dark green soapstone talc, however it is a mixture of approximately 87% amesite and 13 % talc and at the mine was called pyrophyllite. For student purposes, it works as an example of soapstone talc, as these are all considered talcose minerals with similar properties, and only slight differences in chemical composition.
Amesite: Mg2Al(AlSiO5)(OH)4 Talc: Mg3(Si4O10)(OH)2
This was mined at the Frisco Mine in the Talc City Hills, Inyo County, California. This mine was a small producer of high grade talc and was reactivated in 1942 in response to the wartime demand for talc. A large part of production was this dark green pyrophyllite/talc. It was called “chloritic rock” by the US Geological Survey in 1962.
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