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The Silicate Minerals


Talc is Mg3Si4O10(OH)2, always found in metamorphic settings. (more below)
Hydrous magnesium silicate
Photo (c) 2009 Andrew Alden, licensed to About.com (fair use policy)
Talc is the softest mineral, the standard for hardness grade 1 in the Mohs scale. Your fingernail will easily scratch it. Talc has a greasy feel and a translucent, soapy look. Talc and pyrophyllite are very similar, but pyrophyllite (which has Al instead of Mg) may be slightly harder.

This talc specimen comes from somewhere in New York, but talc is quarried throughout the eastern United States, wherever magnesian silicate rocks or dolomite undergoes alteration (steatitization).

Talc is very useful, and not just because it can be ground into talcum powder—it's a common filler in paints, rubber and plastics too. Other less precise names for talc are steatite or soapstone, but those are rocks containing impure talc rather than the pure mineral.

The name talc comes from ancient Persian, through Arabic and Latin.

Other Metamorphic Minerals

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