Тальк-порошок , Talc or Talcum is a clay mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. In loose form, it was one of the most widely used substances known as baby powder, along with corn starch. It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage, and the folia are not elastic, although slightly flexible.
Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 1 as the hardness of talc. As such, talc can easily be scratched by a fingernail. Talc 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 is slightly soluble in dilute mineral acids. Its color ranges from white to grey or green and it has a distinctly greasy feel. Its streak is white.
Talc is used in many industries, including paper making, plastic, paint and coatings, rubber, food, electric cable, pharmaceuticals, cosmetics, and ceramics. A coarse grayish-green high-talc rock is soapstone or steatite, used for stoves, sinks, electrical switchboards, crayons, soap, etc. It is often used for surfaces of laboratory table 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. It is used to coat the insides of inner tubes and rubber gloves during manufacture to keep the surfaces from sticking. Talc, with heavy refinement, has been used in baby powder, an astringent powder used to prevent diaper rash. The American Academy of Pediatrics recommends that parents not use baby powder because it poses a risk of respiratory problems, including breathing trouble and serious lung damage if the baby inhales it. The small size of the particles makes it difficult to keep them out of the air while applying the powder. Zinc oxide-based ointments are a much safer alternative.
It is also often used in basketball to keep a player's hands dry. Most tailor's chalk, or French 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. In the European Union, the additive number is E553b.
Due to its low shear strength, talc is one of the oldest known solid lubricants. Also a limited use of talc as friction-reducing additive in lubricating oils is made.
Talc is widely used in the ceramics industry in both bodies and glazes. In low-fire art-ware 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.