What is Wollastonite?

Wollastonite is named after the English chemist and mineralogist William Hyde Wollaston (1766–1828) and is a calcium inosilicate mineral (CaSiO3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium.

It is usually white but also found in a pearly grey colour.

It forms when impure limestone or dolostone is subjected to high temperature and pressure sometimes in the presence of silica-bearing fluids as in skarns or contact metamorphic rocks.

Associated minerals include garnets, vesuvianite, diopside, tremolite, epidote, plagioclase feldspar, pyroxene and calcite.

Some of the properties that make wollastonite so useful are its high brightness and whiteness, low moisture and oil absorption, low volatility and enhancement of flexural and compaction strcngh. Wollastonite is used primarily in ceramics, friction products (brakes and clutches), metal making, paint filler and plastics.

Despite its chemical similarity to the compositional spectrum of the pyroxene group of minerals where magnesium and iron substitution for calcium ends with diopside and hedenbergite respectively it is structurally very different, with a third SiO4 tetrahedron in the linked chain (as opposed to two in the pyroxenes).


Category - Silicate Mineral

Formula - Calcium Silicate, CaSiO3

Strunz Classification – 09.DG.05

Crystal System - Triclinic, monoclinic polytype exists

Unit Cell - a = 7.925 Å, b = 7.32 Å, c = 7.065 Å; α = 90.055°, β = 95.217°, γ = 103.42°; Z = 6


Colour – White, colourless or grey

Crystal habit – Rare as tabular crystals commonly massive in lamellar, radiating, compact and fibrous aggregates

Crystal Symmetry - Triclinic – pinacoidal H-M symbol: 1 Space group: P1 (1A polytype)

Twinning – Common

Cleavage – Perfect in two directions at near 90˚

Fracture – Splintery to uneven

Luster – Vitreous or dull to pearly on cleavage surfaces

Solubility – Soluble in HCI, insoluble in water

Namwoll produces 5 different sizes of Wollastonite Product:
1.-100 Micron
2.-150 Micron
3.-1200 Micron
4.-25 Micron
5.-200 Micron
Retained on cumulative
250 micron0.05%
150 micron6 - 8 %
100 micron15 - 17%
75 micron39 - 44%
45 micron72 - 74%
Calcium CaO46.5 – 47.5
Magnesium MgO0.16 – 0.3
Silica SiO248 – 49.5
Sodium Na2OTrace
Potassium K2O30.08 – 0.88
Phosphorus P2O50.01 – 0.05
Titanium TiO20.03 – 0.04
Iron Fe2O30.5 – 0.55
Aluminium Al2O30.8 – 0.9
L.O.I.2.6 – 2.7
pH9.8 - 10
Moisture (110 dec C at 24 hrs)0.5
Oil Absorption14-15g/100g
Refractive Index1.63
Hardness moh4.5 – 5.0
Whiteness SABS 137 Dry80 - 85
Specific gravity2.8 - 2.9
Melting Point1540c