Wollastonite

In short

Wollastonite is a white, needle-like or fibrous mineral made of calcium, silicon and oxygen (CaSiO₃). It forms when impure limestone is heated by contact with hot magma, so it is found with minerals such as garnet and diopside in the skarn zone between limestone and igneous rock. It is an industrial raw material because it reduces shrinkage and gas release in ceramic firing, serves as a filler in paint and plastics and can replace asbestos. China produces most of the world's wollastonite; the deposits in Türkiye are small.

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How to recognise it

1. 1

   White, colourless or grey-white (it can also be brown, yellow, red or pale green); it often forms long bundles of silky or glassy needles and tabular masses. Pearly lustre shows on cleavage faces.

2. 2

   Mohs hardness is 4.5–5: the tip of a steel knife scratches it, but it does not scratch glass. Its density is about 2.9–3 g/cm³.

3. 3

   Fibrous masses split easily along their fibres; the Handbook of Mineralogy speaks of parallel fibrous masses with perfect cleavage. The streak is white.

4. 4

   It is usually intergrown with minerals such as calcite, garnet (grossular), diopside, vesuvianite and epidote at the boundary of limestone and igneous rock. A microscope or X-ray diffraction is needed for a sure identification.

Myths and misconceptions

• MythWollastonite is a kind of asbestos.

  FactWollastonite is not asbestos but a calcium silicate mineral (CaSiO₃, of the pyroxenoid group). Because its needle-like habit resembles asbestos, it is used in place of asbestos in floor tiles, brake linings, insulating board, paint, plastics and roofing products (USGS, Wikipedia).

• MythWollastonite is a calcium carbonate like calcite.

  FactWollastonite is a calcium silicate, not a carbonate; it holds no carbon. The calcite in limestone reacts with quartz and releases carbon dioxide as it turns into wollastonite. It is useful in ceramics partly because, unlike calcite, it gives off no gas during firing.

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Where is it found?

• Willsboro, Essex County, New York, USA · Major depositAccording to Wikipedia, wollastonite in the USA is mined in Willsboro and Gouverneur, New York; according to the USGS, New York is the only state with long-term continuous mining. The point is the position of the town of Willsboro.
• Lappeenranta, South Karelia, Finland · Major depositLappeenranta in south-eastern Finland is among the places whose commercial wollastonite is often analysed in the literature (Çınku et al., 1997); the USGS counts Finland among the countries with large wollastonite deposits. The point is the position of the city of Lappeenranta.
• Pilares deposit, 55 km north of Hermosillo, Sonora, Mexico · Major depositThe Handbook of Mineralogy lists the Pilares deposit, 55 km north of Hermosillo, as one of the large deposits in Mexico. According to the USGS, Mexico produced about 112,000 tons of wollastonite in 2024. The point is an approximate match for that description.
• Rajasthan (Sirohi, Dungarpur, Udaipur, Pali and Ajmer districts), India · Major depositAccording to the Indian Bureau of Mines the main deposits lie in the Ajmer, Dungarpur, Pali, Sirohi and Udaipur districts of Rajasthan; the output of about 108,000 tons in 2021-22 came entirely from private-sector mines in Rajasthan. The point is the general position of the region.
• Dognecea, Caraș-Severin County, Romania · Historic sourceThe Handbook of Mineralogy lists Dognecea and Csiklova (Ciclova) in the Banat region of Romania among the prominent wollastonite localities. The point is the position of the village of Dognecea.
• Monte Somma and Vesuvius, Campania, Italy · Historic sourceThe Handbook of Mineralogy lists Sarrabus in Sardinia and Monte Somma and Vesuvius among the prominent Italian wollastonite localities. The point is the position of Vesuvius.
• Serçeören village area, Kepsut, Balıkesir, Türkiye · Major depositAccording to Erdinç (1984), Türkiye's first wollastonite production came from here in 1968; in the contact-metamorphic zone north-west of the village, wollastonite occurs in calc-silicate rocks with garnet, diopside, forsterite, vesuvianite and tremolite. About 500,000 tons of reserves are estimated and about 100,000 tons of pure wollastonite have been mined intermittently for the ceramics industry. The point is the position of the town of Kepsut.
• Tahtaköprü area (Demir Tepe), İnegöl, Bursa, Türkiye · Known localityAccording to Demange et al. (1998), the wollastonite-garnet skarns of Demir Tepe are developed in graphitic marbles that form roof pendants in the Tertiary Göynükbelen granodiorite pluton. In the table of Çınku et al. (1997) the Meşrutiye–Tahtaköprü deposit, at about 1.07 million tons (probable reserve), is Türkiye's largest recorded wollastonite reserve. The point is the position of the town of İnegöl.
• Karaköy area, Bayramiç, Çanakkale, Türkiye · Known localityAccording to Çınku et al. (1997), in the Kurcatepe–Katırlıkuyu pit 3 km north-east of Karaköy, in the Karakaya series of the Evciler pluton on the Biga Peninsula, fibrous wollastonite occurs with actinolite, garnet, epidote and calcite. The visible reserve was put at only 7,500 tons in 1996. The point is the position of the town of Bayramiç.
• Kırşehir Massif (Tamadağ Formation), Türkiye · Known localityAccording to Özkol and Kulaksız (1995), in the Kırşehir Massif, especially the Tamadağ Formation, 10–40 percent of the marble-like and calc-schist rocks is wollastonite; the occurrences form bands 1000 × 50–150 m in extent. The authors treat the area as a possible source of industrial raw material. The point is the position of the city of Kırşehir.

Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →