Wollastonite
Wollastonite, CaSiO3: a calcium silicate of skarns and metamorphosed limestone, hardness 4.5–5, density 2.86–3.09, with its IMA rows, polytypes and USGS uses.
Wollastonite is calcium silicate, CaSiO3 on the September 2026 IMA list: a white to colourless mineral, hardness 4.5 to 5, density 2.86 to 3.09, cleaving perfectly on {100} and often parallel fibrous. It forms where siliceous carbonates are heated, in skarns at intrusive contacts. The USGS lists ceramics, brake linings, paint and plastics among its uses.
In short
- The formula. The September 2026 IMA-CNMNC Master List lists wollastonite as CaSiO3, status A, 1962 s.p., Romania; the Handbook of Mineralogy sheet writes the same. Worked, that is 48.28% CaO and 51.72% SiO2. The sheet gives monoclinic or triclinic, crystals to 20 cm, cleavage {100} perfect, hardness 4.5 to 5, density 2.86 to 3.09, white, colourless, brown, red, yellow or pale green, streak white.
- The CaSiO3 ledger. A script over the IMA list finds three rows written exactly CaSiO3: wollastonite (A, 1962 s.p., Romania), pseudowollastonite (A, 1962 s.p., Iran) and davemaoite (A, 2020-012a, Botswana). Breyite, Ca3Si3O9 (A, 2018-062, Brazil), has the same proportions. The sheet’s polytypes 1A, 2M, 3A, 4A, 5A and 7A have no rows of their own, and “parawollastonite” occurs nowhere in the list.
- The Broken Hill check. Recast on three oxygens, the sheet’s Remonmaki, Finland analysis is Ca 1.006 Si 0.991, calcium 99.1% of the non-silicon cations. The North mine, Broken Hill, New South Wales, analysis is Ca 0.763, Mn 0.137, Fe 0.092: calcium 76.8%, still leading, against 50% in bustamite, Mn2Ca2MnCa(Si3O9)2 on the IMA list.
- Where it forms and what it is used for. “Common in thermally metamorphosed siliceous carbonates, the intruding igneous rock, and skarn deposits along their contact”, with calcite, grossular, diopside and vesuvianite as associates. USGS Mineral Commodity Summaries 2026 lists ceramics, friction products, metallurgical flux, paint and plastics, with 860,000 t mined worldwide in 2025.
- Documented failure: the balance. A 20.00 g piece reads 13.01 to 13.53 g in water. At the low end that is exactly dolomite (13.01 g) and close to calcite (12.62 g), the carbonates it grows from, so the balance cannot clear a white skarn mineral. Hardness can: 4.5 to 5 against 3 for calcite and 3.5 to 4 for dolomite.
| Row | Formula | IMA status, year, country | Ca share of Ca+Mn+Fe+Mg | Density | Note, as printed or worked |
|---|---|---|---|---|---|
| Wollastonite | CaSiO3 | A, 1962 s.p., Romania | 1 (formula) | 2.86–3.09 meas.; 2.90 calc. | Polytypes 1A, 2M, 3A, 4A, 5A, 7A on the sheet; none is an IMA row |
| Pseudowollastonite | CaSiO3 | A, 1962 s.p., Iran | 1 (formula) | — | No Handbook sheet: the URL returned an HTML page, not a PDF, on 14 November 2026 |
| Davemaoite | CaSiO3 | A, 2020-012a, Botswana | 1 (formula) | — | First reference Science 374 (2021), 891 |
| Breyite | Ca3Si3O9 | A, 2018-062, Brazil | 1 (formula) | — | Same Ca:Si:O as CaSiO3, written on a 3-formula basis |
| Wollastonite, Remonmaki, Finland | Ca1.006Mg0.006Fe0.003Si0.991O3 (recast) | Sheet analysis (1) | 0.991 | — | Sheet prints (Ca1.01Mg0.01)Σ=1.02Si0.99O3: reproduces |
| Wollastonite, North mine, Broken Hill | Ca0.763Mn0.137Fe0.092Si0.995Al0.011O3 (recast) | Sheet analysis (2) | 0.768 | — | Sheet prints (Ca0.76Mn0.14Fe0.09)Σ=0.99(Si1.00Al0.01)Σ=1.01O3: reproduces |
| Wollastonite cells (sheet) | P21/a, Z = 12; P-1, Z = 6 | — | — | 2.917 and 2.909 from the cells | 66.12 and 66.30 ų per CaSiO3, against the printed 2.90 |
What is the chemical formula of wollastonite?
CaSiO3. The September 2026 IMA list gives wollastonite as CaSiO3, status A, 1962 s.p., with Romania as the country; the list’s first reference is Nouveau Dictionnaire d’Histoire Naturelle 20 (1818), 28. The Handbook of Mineralogy wollastonite sheet prints the same formula. On standard atomic weights the formula mass is 116.16, and the mineral is 34.50% calcium, 24.18% silicon and 41.32% oxygen by mass, or 48.28% CaO and 51.72% SiO2. It is a silicate; the carbonate it often replaces is the subject of is calcite a silicate.
What the sheet records. Monoclinic or triclinic, point group 2/m or -1. Crystals tabular on {100} or {001}, or short to long prismatic, to 20 cm; commonly cleavable, parallel fibrous, or compact and massive; twinning common, twin axis [010], composition plane {100}. Cleavage {100} perfect, {001} and {-102} good, with (100) to (001) at 84.5°. Fracture uneven; brittle. Hardness 4.5 to 5; density 2.86 to 3.09 measured, 2.90 calculated. White, colourless, brown, red, yellow or pale green; streak white; vitreous, pearly on cleavage. Biaxial (−), α 1.616 to 1.640, γ 1.631 to 1.653. It “May exhibit yellow catholuminescence”, the sheet’s spelling; it prints no fluorescence.
Name. “For William Hyde Wollaston (1766–1828), English chemist and mineralogist.”
Is wollastonite one mineral? The CaSiO3 ledger
One name, several structures. The sheet’s Polymorphism field lists “1A, 2M, 3A, 4A, 5A, 7A polytypes”, and two cells: monoclinic P21/a with Z = 12, and triclinic P-1 with Z = 6. One of its references is titled “wollastonite-2M (parawollastonite)”. On the IMA list these are not separate species: a text search finds no row beginning Wollastonite- and no occurrence of parawollastonite. A label reading parawollastonite is wollastonite.
The other CaSiO3 rows. Pseudowollastonite, CaSiO3, A, 1962 s.p., Iran, is a separate species on the list; its Handbook sheet URL returned an HTML page, not a PDF, on 14 November 2026, so this page gives no figures for it. Davemaoite, CaSiO3, A, 2020-012a, Botswana, first reference Science 374 (2021), 891. Breyite, Ca3Si3O9, A, 2018-062, Brazil, has the same calcium-silicon-oxygen ratio. Ten parsed rows contain calcium, silicon and oxygen only; these four are the 1:1:3 ones.
A cell check. Both printed cells give the same packing: 66.12 ų per CaSiO3 in the monoclinic cell and 66.30 in the triclinic, densities of 2.917 and 2.909, against the printed calculated 2.90. That is consistent with polytypes being stacking variants of one composition, which is how the sheet lists them.
Where is wollastonite found? Skarns and heated limestone
The Occurrence field. “Common in thermally metamorphosed siliceous carbonates, the intruding igneous rock, and skarn deposits along their contact; also in some alkalic igneous rocks and carbonatites.” Its associates are calcite, grossular, diopside, vesuvianite, åkermanite, merwinite, larnite and spurrite. The USGS 2026 summary says economic deposits typically form by thermal metamorphism of siliceous limestone, or by alteration of limestone by siliceous hydrothermal fluids along faults or contacts with magmatic intrusions. The hedenbergite page names Broken Hill and Fe–Mn skarns on its own sheet.
The Distribution field, as printed. “A widely distributed mineral”; prominent localities include Dognecea and Csiklova, Banat, Romania; Sarrabus, Sardinia, and Monte Somma and Vesuvius, Italy; Dunmorehead, Mourne Mountains, and Scawt Hill, near Larne, Co. Antrim, Ireland; Kongsberg, Norway; Göckum, Sweden; Harzburg and Auerbach, Germany; Natural Bridge and Diana, Lewis Co., New York, Crestmore and Darwin, California, and a large deposit near Gilbert, Nevada, USA; Oka and Asbestos, Quebec, and Outlet Post, Ontario, Canada; Pichucalo and the Pilares deposit, Mexico; three localities in Japan; and large crystals from Belafa, Madagascar.
The Broken Hill check. The sheet’s second analysis, from the North mine, Broken Hill, recasts to Ca 0.763, Mn 0.137 and Fe 0.092 per three oxygens: calcium is 76.8% of the non-silicon cations, so it is still wollastonite. In bustamite, Mn2Ca2MnCa(Si3O9)2 on the IMA list, calcium is half. Bustamite is a comparator on the rhodonite page; the sodium-bearing relative, pectolite (and its manganese analogue serandite), is a different formula, NaCa2Si3O8(OH).
What is wollastonite used for? What the USGS says
Uses, as listed. The USGS Mineral Commodity Summaries 2026, wollastonite says ceramics (frits, sanitaryware and tile), friction products (primarily brake linings), metallurgical applications (flux and conditioner), paint, plastics and rubber, and miscellaneous uses including adhesives, concrete, glass and sealants accounted for US sales. It says wollastonite is used as a substitute for asbestos in floor tiles, friction products, insulating board, paint, plastics and roofing products. The summary does not mention agricultural or plant uses, so this page makes none.
Production, worked. World mine production was about 860,000 t in 2025 (estimated): China 600,000, India 120,000, Mexico 100,000 and Canada 30,000, with US output withheld. China is 69.8% of the rounded total and India 14.0%. The summary names two companies mining in New York and says New York is the only US state with long-term continuous mining. It gives no breakdown by Indian state.
Fibrous habit. The sheet records parallel fibrous material. Questions about fibrous minerals go to toxic minerals in a collection; this page is not health or safety advice. More species are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.