Talc (derived from the Arabic: talk) is a silicate mineral, the standard for hardness grade 1 in the Mohs scale. Your fingernail will easily scratch it. Talc is composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc and pyrophyllite are very similar, but pyrophyllite may be slightly harder.
Talc has a greasy feel and a translucent, soapy look. In loose form, it is the widely-used substance known as talcum powder. Steatite, also called soapstone, is a rock with a lot of talc.