Soapstone

Soapstone (also known as steatite or soaprock) is a talc-schist, which is a type of metamorphic rock. It is composed largely of the magnesium rich mineral talc. It is produced by dynamothermal metamorphism and metasomatism, which occur in the zones where tectonic plates are subducted, changing rocks by heat and pressure, with influx of fluids, but without melting. It has been a medium for carving for thousands of years. The definitions of the terms "steatite" and "soapstone" vary with the field of study. In geology, steatite is a rock that is to a very large extent composed of talc. The mining industry will define steatite as a high-purity talc rock that is suitable for manufacturing of, for example, insulators, the lesser grades of the mineral can be called simply "talc rock". Steatite can be used both in lumps ("block steatite", "lava steatite", "lava grade talc"), and in the ground form. While the geologists logically will use "steatite" to designate both forms, in the industry "steatite" without additional qualifications typically means the steatite that is either already ground or the one to be utilized in the ground form in the future. If the ground steatite is pressed together into blocks, these are called "synthetic block steatite", "artificial block steatite", "artificial lava talc". In industrial applications soapstone refers to dimension stone that consists of either amphibole-chlorite-carbonate-talc rock, talc-carbonate rock, or simply talc rock and is sold in the form of sawed slabs. "Ground soapstone" sometimes designates the ground waste product of the slab manufacturing. Petrologically, soapstone is composed dominantly of talc, with varying amounts of chlorite and amphiboles (typically tremolite, anthophyllite, and cummingtonite, hence its obsolete name, magnesiocummingtonite), and traces of minor iron-chromium oxides. It may be schistose or massive. Soapstone is formed by the metamorphism of ultramafic protoliths (e.g. dunite or serpentinite) and the metasomatism of siliceous dolomites.