|Monthly Tech-Tip |
Talc is also called steatite (it is a magnesium silicate hydrate). It is the main component of soapstone, it is the softest of all minerals (Mohs hardness of 1). Its silicate layers are weakly bound, this is the reason for the characteristic greasy or soapy feeling. It's color depends on the impurities (it can be colourless, white, grey, green, yellow or pink). It often it has a mother-of-pearl sheen.
Like dolomite and calcium carbonate, it has the curious property of being refractory when used pure but being a flux when combined with other materials.
Steatite is also a manufactured ceramic, a crystalline form of magnesium silicate (called synthetic steatite). It has relatively good strength and can service at temperatures up to 2,000°F (1180°C). It is much less expensive than sintered ceramics like alumina or zirconia. It's pressed density determines the porosity, compressive and flexural strength, conductivity and resistivity of the part being made.
Steatite is popular for making ceramic components where there is no need for tight dimensional tolerances, chemical purity or high mechanical stress - a common application is parts for electrical heaters.
Soapstone Steatite Carving
Talc Mineralogy at Mondo Minerals
Steatite properties page at Associated Ceramics
Soapstone at Wikipedia
In the ceramic industry, refractory materials are those that can withstand a high temperature without deforming or melting. Refractories are used to build and furnish kilns.