TALC, an orthorhombic mineral oc curring in short hexagonal prisms and plates, also in globular and stellated groups, compact, massive. Cleavage, basal; luster, pearly; color, apple-green, white, shades of gray; sectile; feel, greasy. Composition, varying with the amount of water present, but essentially a hydrated silicate of magnesia which, when pure, would contain: Silica, 62.0; magnesia, 33.1; water 4.9=100, the for mula being 6111g05Si02+2H0. Dana di vides as follows: (1) Foliated; (2) mas sive (steatite or soapstone) ; (a) Coarse granular, including potstone; (b) Cryp to-crystalline (French chalk) ; (c) Rens selwriate, cryptocrystalline, but more often pseudomorphous; (d) Indurated, a very abundant mineral. Being thor oughly incombustible it is of great value in the manufacture of fireproof wall pa per, paper window curtains, etc. Even in its crude state it is found to yield one of the best lubricants known. Mixed with common grades of soap, it makes them as pleasant to the touch as the choicest brands. It is also largely used
in the manufacture of patent wall plas ter, in which its addition gives a smooth, glossy finish to walls and ceilings that no other substance lends. Talc powder, duly refined, is exquisitely soft and fine grained. So, too, it makes an unsur passed molding sand for casting metals in, both its fireproof and fire-grained qualities being very valuable in fine work. Mixed with rubber, it renders it more elastic and less liable to crack. From it is also made the "French chalk" used by tailors, and shoe dealers use it in pow dered form to enable one to pull on a tight-fitting shoe. The principal talc mines in the U. S. are in St. Lawrence co., N. Y. Virginia and the western part of North Carolina produces the purest soapstone. Also a commercial name for mica (q. v.).
Oil of talc: A cosmetic common in the 17th century, consisting of talc calcined. See SOAPSTONE.