wollastonite

Wollastonite is a calcium silicate mineral with the chemical formula CaSiO3. It forms in metamorphic environments, particularly in contact metamorphic skarns where limestone or dolostone reacts with silica-rich magmas. The mineral is part of the pyroxenoid group of silicates and commonly occurs as white to gray, glassy to fibrous crystals. It was named after William Hyde Wollaston, who first described it in the early 19th century.

Wollastonite occurs worldwide in skarn-bearing zones and metamorphic belts. Major deposits have been mined in Finland, Italy, Norway, Spain, China, and the United States, often in association with calc-silicate rocks. The natural material is processed to produce crude ore, concentrates, and fine powders for industrial use.

In terms of properties, wollastonite is typically white or pale and may display a glassy to silky luster. It has a hardness around 4.5 to 5 on the Mohs scale and a density near 2.9 g/cm3. It occurs as massive, granular, or acicular (fibrous) aggregates and is valued for its chemical inertness, brightness, and relatively high thermal stability. Its low thermal expansion makes it useful as a filler and reinforcement in various materials.

Industrially, wollastonite is used as a white filler in paints, plastics, rubber, and paper; in ceramics and glazes to enhance strength and whiteness; as a flux in glass and enamel formulations; and as an additive in cement and other construction materials. The fibrous variety has raised safety considerations, and respirable wollastonite dust can irritate the respiratory tract. When present with asbestos-like contaminants, appropriate safety measures are required to protect workers.

Overall, wollastonite is valued for its whiteness, inertness, and thermal properties, supporting a range of applications across coatings, plastics, ceramics, and construction.