| Wollastonite | |
|---|---|
 | |
| General | |
| Category | Inosilicate mineral |
| Formula (repeating unit) | Calcium metasilicate, CaSiO3 |
| IMA symbol | Wo[1] |
| Strunz classification | 9.DG.05 |
| Crystal system | Triclinic Monoclinic polytype exists |
| Crystal class | Pinacoidal (1) (same H-M symbol) |
| Space group | P1 (Triclinic) P21/a (Monoclinic) |
| 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 | |
| Formula mass | 116.159 g/mol |
| Color | White, colorless or gray |
| Crystal habit | Rare as tabular crystals—commonly massive in lamellar, radiating, compact and fibrous aggregates. |
| Twinning | Common |
| Cleavage | Perfect in two directions at near 90° |
| Fracture | Splintery to uneven |
| Mohs scale hardness | 4.5 to 5.0 |
| Luster | Vitreous or dull to pearly on cleavage surfaces |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.86–3.09 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.616–1.640 nβ = 1.628–1.650 nγ = 1.631–1.653 |
| Birefringence | δ = 0.015 max |
| 2V angle | Measured: 36° to 60° |
| Melting point | 1540 °C |
| Solubility | Soluble in HCl, insoluble in water |
| Other characteristics | Heat of formation (@298): −89.61kJ Gibbs free energy: 41.78kJ |
| References | [2][3][4][5][6] |
Wollastonite is a calcium inosilicate mineral (CaSiO3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure limestone or dolomite is subjected to high temperature and pressure, which sometimes occurs in the presence of silica-bearing fluids as in skarns[7] or in contact with metamorphic rocks. Associated minerals include garnets, vesuvianite, diopside, tremolite, epidote, plagioclase feldspar, pyroxene and calcite. It is named after the English chemist and mineralogist William Hyde Wollaston (1766–1828).
Despite its chemical similarity to the compositional spectrum of the pyroxene group of minerals—where magnesium (Mg) and iron (Fe) substitution for calcium ends with diopside and hedenbergite respectively—it is structurally very different, with a third SiO4−4 tetrahedron[8] in the linked chain (as opposed to two in the pyroxenes).
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Wollastonite, Mindat
- ^ Wollastonite, Webmineral
- ^ Wollastonite, Handbook of Mineralogy
- ^ American Mineralogist, V. 79, pp. 134-144, 1994
- ^ Virta, Robert; Van Gosen, Brad (January 27, 2015). "Mineral Resource of the Month: Wollastonite". Earth Magazine. American Geosciences Institute.
- ^ Whitley, Sean; Halama, Ralf; Gertisser, Ralf; Preece, Katie; Deegan, Frances M.; Troll, Valentin R. (2020-10-18). "Magmatic and Metasomatic Effects of Magma–Carbonate Interaction Recorded in Calc-silicate Xenoliths from Merapi Volcano (Indonesia)". Journal of Petrology. 61 (4). doi:10.1093/petrology/egaa048. ISSN 0022-3530.
- ^ William Alexander Deer; Robert Andrew Howie; J. Zussman (1992). An introduction to the rock-forming minerals. Longman Scientific & Technical. ISBN 978-0-470-21809-9.