Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. It occurs as foliated to fibrous masses, its monoclinic crystals being so rare as to be almost unknown. It has a perfect basal cleavage, the folia non-elastic although slightly flexible. It is sectile and very soft, with a hardness of 1. It has a specific gravity of 2.5-2.8, a waxlike or pearly lustre, and is translucent to opaque. Its color ranges from white to gray or green and it has a distinctly greasy feel.
Talc is a metamorphic mineral resulting from the alteration of silicates of magnesium such as pyroxenes, amphiboles, olivine and other similar minerals. It is usually found in metamorphic rocks, often of a basic type due to the alteration of the minerals mentioned above.
A coarse grayish-green talc has been called soapstone or steatite and has been used for stoves, sinks, electrical switchboards, etc. Talc finds use as a cosmetic (talcum powder), as a lubricant, and as a filler in paper manufacture. Most tailor's chalk is talc.
See also: List of minerals