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 strength. 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).
Wollastonite in nature. Fine Crystals.
Wollastonite in nature. Cluster of crystals with carnet and dioptase inclusions.
Wollastonite cluster.
Wollastonite cluster.
Wollastonite needles under a microscope.
Wollastonite end product.
General
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
Identification
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
| IncWoll produces 5 different sizes of Wollastonite Product: | |
|---|---|
| 1. | -100 Micron |
| 2. | -150 Micron |
| 3. | -1200 Micron |
| 4. | -25 Micron |
| 5. | -200 Micron |
| PARTICULAR SIZE DISTRIBUTION | MICRON |
|---|---|
| Retained on cumulative | |
| 250 micron | 0.05% |
| 150 micron | 6 - 8 % |
| 100 micron | 15 - 17% |
| 75 micron | 39 - 44% |
| 45 micron | 72 - 74% |
| CHEMICAL ANALYSIS | % |
|---|---|
| Calcium CaO | 46.5 – 47.5 |
| Magnesium MgO | 0.16 – 0.3 |
| Silica SiO2 | 48 – 49.5 |
| Sodium Na2O | Trace |
| Potassium K2O3 | 0.08 – 0.88 |
| Phosphorus P2O5 | 0.01 – 0.05 |
| Titanium TiO2 | 0.03 – 0.04 |
| Iron Fe2O3 | 0.5 – 0.55 |
| Aluminium Al2O3 | 0.8 – 0.9 |
| L.O.I. | 2.6 – 2.7 |
| PHYSICAL PROPERTIES | % |
|---|---|
| pH | 9.8 - 10 |
| Moisture (110 dec C at 24 hrs) | 0.5 |
| Oil Absorption | 14-15g/100g |
| Refractive Index | 1.63 |
| Hardness moh | 4.5 – 5.0 |
| Whiteness SABS 137 Dry | 80 - 85 |
| Specific gravity | 2.8 - 2.9 |
| Melting Point | 1540c |
| Appearance | White |
| Shape | Acicular |