Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its monoclinic crystals being so rare as to be almost unknown. It has a perfect basal cleavage, and the folia are non-elastic, although slightly flexible. It is very soft and sectile (can be cut with a knife); as the defining mineral for the value of 1 on Mohs hardness, it can be easily scratched by a fingernail. It has a specific gravity of 2.5–2.8, a clear or dusty luster, and is translucent to opaque. Talc is not soluble in water, but it is slightly soluble in dilute mineral acids. Its colour ranges from white to grey or green and it has a distinctly greasy feel. Its streak is white.

Talc is used in many industries such as paper making, plastic, paint and coatings, rubber, food, electric cable, pharmaceuticals, cosmetics, ceramics, etc. A coarse grayish-green high-talc rock is soapstone or steatite and has been used for stoves, sinks, electrical switchboards, crayons, soap, etc. It is often used for surfaces of lab counter tops and electrical switchboards because of its resistance to heat, electricity and acids.

Talc finds use as a cosmetic (talcum powder), as a lubricant, and as a filler in paper manufacture. Talc is used in baby powder, an astringent powder used for preventing rashes on the area covered by a diaper (see diaper rash). It is also often used in basketball to keep a player's hands dry. Most tailor's chalk is talc, as is the chalk often used for welding or metalworking.

Talc is also used as food additive or in pharmaceutical products as a glidant. In medicine talc is used as a pleurodesis agent to prevent recurrent pleural effusion or pneumothorax.

Talc is widely used in the ceramics industry in both bodies and glazes. In low-fire artware bodies it imparts whiteness and increases thermal expansion to resist crazing. In stonewares, small percentages of talc are used to flux the body and therefore improve strength and vitrification. It is a source of MgO flux in high temperature glazes (to control melting temperature). It is also employed as a matting agent in earthenware glazes and can be used to produce magnesia mattes at high temperatures.