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Chemistry and Morphology
Talc's scientific name is hydrated magnesium silicate or magnesium silicate hydroxide. Its chemical formula is written as 3MgO.4SiO2H2O. Talc is a secondary mineral created through the interaction of water, heat and pressure to form a metamorphic rock from other magnesium-rich rocks such as dolomite, serpentine, and dunnite.
Talc is found in three forms: fibrous, non fibrous and massive. Its hardness is determined by different amounts of magnesium, silicates and other associated minerals. Talc is chemically inert and is nonreactive with either acids or bases.
Types
When talc is compressed into a cohesive mass in the earth with few impurities, it forms soapstone or steatite. Hard talc containing more mineral impurities is darker in color and is called potstone.
The fibrous and non fibrous types contain more impurities, are less desirable for many consumer products and are used more often in industrial applications and paints.
Appearance
When compacted into soapstone, potstone or steatite, talc has a dull or pearlescent appearance. Soapstone and steatite are very light or white in color, while potstone is darker and duller. Pulverized talc is white, making it a good choice for including in cosmetics. The coarser fibrous types are green or gray because of the higher amounts of other minerals they contain.
The various forms of talc have a soapy or greasy feeling, one of its main identifiers. Even in it compact form, talc is soft and can be easily scratched with a fingernail.
Uses
Soapstone, steatite and potstone in their compact form can be carved into vases, statues, bowls and similar small items. The quality also makes soapstone a valuable material for manufacturing solid-fuel stove tiles and laboratory table tops. When pulverized and processed during manufacturing, talcum powder is a major constituent of face and body preparations. It also has applications as an inert ingredient in agricultural products, paper making, paint formulation, electrical insulation, plastics, polishes and soaps. Pulverized steatite is processed and reconstituted into sheets and bricks from which non conductive wafers, cylinders and discs are cut for use in electronics.
Geography and Geology
Large amounts of talc are mined in Austria, Canada, France and Italy. In the United States, the mineral is mined extensively in California, Georgia, Montana, North Carolina and Texas. Its various forms are found as bands, plates and veins in conjunction with related minerals such as dolomite. The deposits may consist of small rocks or large boulders measuring several feet in length and width.