A white nonmetallic, natural mineral identified chemically as calcium metasilicate, CaSiO3. It is the only commercially available pure white mineral that is wholly acicular (needle-like crystals).
The fibrous form of wollastonite can be very beneficial in bodies. In low fired ceramics wollastonite reduces drying and firing shrinkage and drying and firing warpage. It also promotes lower moisture and thermal expansion in the fired product and increases firing strength. It fires with no LOI and its fibers help vent out gassing. These factors have made it a valuable component in tile bodies, especially for fast fire.
Wollastonite is used as a major flux in high temperature sanitary ware, tile and electrical insulators (augmenting feldspar and silica, pushing their percentages down very significantly).
At higher temperatures the powdered form is valuable as a source of CaO flux in glazes (and bodies). The other main raw source of CaO is whiting but it releases a high volume of gases of decomposition which produce suspended micro-bubbles that demand slow firing to clear. Also, since wollastonite sources silica as well, glaze recipes employing it do not need as much raw silica powder, especially at lower temperatures (since the wollastonite is sourcing SiO2). Wollastonite’s greater readiness to melt at higher temperatures has a curious side effect: Glazes can tolerate higher SiO2 (from the Wollastonite) and melt just as well or better.