Wollastonite is named after the English chemist and mineralogist, William Hyde Wollaston. There are a number of monoclinic and triclinic polytypes of Wollastonite, which are as follows: Wollastonite-1A, Wollastonite-2M, Wollastonite-3Å, Wollastonite-4Å, Wollastonite-5Å, and Wollastonite-7Å. Structurally, wollastonite is composed of of the repeating unit (Si3O9)6-.
Properties of Wollastonite
The properties of Wollastonite are given below:
- Cell Data
- Space Group: P21 / a
- a = 15.409(3)
- b = 7.322(1)
- c = 7.063(1)
- β = 95.30(2)°
- Z = 12
- Space Group: P1
- a = 7.94
- b = 7.32
- c = 7.07
- α = 90°2’
- β = 95°22’
- γ = 103°26’
- Z = 6
- Crystal Data
- Monoclinic or triclinic
- Point group: 2/m or 1.
- Commonly cleavable, parallel fibrous, or compact, massive.
- Crystals tabular // {100} or {001}, or short to long prismatic, to 20 cm.
- Twinning: Common
- Twin axis [010]
- Composition plane (100g)
- Chemical Composition
| Elements |
1 |
2 |
| SiO2 |
50.82 |
50.24 |
| CaO |
48.16 |
35.93 |
| FeO |
0.18 |
5.54 |
| MnO |
0.03 |
8.16 |
| MgO |
0.22 |
0.07 |
| Na2O |
0.12 |
- |
| Al2O3 |
- |
0.46 |
| H2O+ |
0.08 |
0 |
| K2O |
0.07 |
- |
| S |
- |
0.14 |
| Fe2O3 |
- |
trace |
| Total |
99.68 |
100.54 |
- Optical Properties
- Optical class: Biaxial (-).
- Orientation: X ^ c = 30°-44°; Y ^ b = 0°-5°; Z ^ a =37°-50°.
- Dispersion: r > v, weak. α = 1.616-1.640; β = 1.628-1.650; γ = 1.631-1.653
- 2V (meas.) = 36°-60°
- Estimated Properties
| Electron density |
Bulk density (electron density)=2.91 gm/cm3. note: Specific gravity of wollastonite-1A =2.91 gm/cm3 |
| Photoelectric |
PEWollastonite-1A = 5.15 barns/electron U=PEWollastonite-1A x Electron Density= 14.97 barns/cm3 |
| Fermion index |
Fermion Index = 0.01 Boson Index = 0.99 |
| Radioactivity |
GRapi = 0 (Gamma Ray American Petroleum Institute Units) Wollastonite-1A is Not Radioactive |
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How to Identify Wollastonite
Wollastonite can be identified in the field by its thin, elongated fractures produced by intersecting cleavages or partings. Its crystals do not produce stellar forms and radiate from the center. It is found in sub-transparent to translucent forms in white, yellow, gray, red, and brown colors. It also has a vitreous silky lustre with a white streak. Wollastonite has a density range ranging between 2.8 and 2.9, and a hardness of 5 (approximate to apatite).
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Uses of Wollastonite
Wollastonite is a very important mineral that is globally used in various industries. The following are some of the significant applications of this mineral:
- In tile factories it is added into the manufacturing of ceramics so as to improve the overall quality, as wollastonite has whiteness, fluxing properties, freedom from volatile constituents,and an acicular particle shape.
- In the ceramics sector, wollastonite aids in decreasing shrinkage and gas evolution during firing, increasing green and fired strength, maintaining brightness during firing, allowing fast firing, and reducing crazing, cracking, and glaze defects.
- In the metallurgy industry, wollastonite acts as a flux for welding, a source for calcium oxide, and a slag conditioner. It also protects the surface of molten metal during the continuous casting of steel.
- In the paint sector, wollastonite is an additive to improve the durability of the paint film. It acts as a pH buffer, reduces gloss, decreases pigment consumption, improves its resistance to weathering, and acts as a flatting and suspending agent.
- In plastics, wollastonite enhances tensile and flexural strength, decreases resin consumption, and improves thermal and dimensional stability at very high temperatures. Surface treatments are required to enhance the adhesion between wollastonite and the polymers to which it is added.
Further uses include:
- Wollastonite acts as a substitute for asbestos in floor tiles, friction products, insulating board and panels, paint, plastics, and roofing products.
- Wollastonite is resistant to chemical attack, inert, stable at high temperatures, and improves flexural and tensile strength.
Global Distribution
Wollastonite is a widely distributed mineral. The following are some of the significant localities:
- Romania -Dognecea (Dognaczka) and Csiklova, Banat
- Germany -Harzburg, Harz Mountains, and Auerbach, Odenwald, Hesse.
- Italy -Sarrabus, Sardinia, and from Monte Somma and Vesuvius, Campania
- Kongsberg, Norway
- GÄockum, Sweden
- Ireland -Dunmorehead, Mourne Mountains, and Scawt Hill, near Larne, Co. Antrim
- Canada -Oka and Asbestos, Quebec; at Outlet Post, Leeds Co., Ontario.
- USA -Natural Bridge and Diana, Lewis Co., New York; from Crestmore, Riverside Co., and Darwin, Inyo Co., California; in a large deposit two miles southeast of Gilbert, Esmeralda Co., Nevada.
- Mexico -Pichucalo, Chiapas, and in the Pilares deposit, 55 km north of Hermosillo, Sonora
- Madagascar large crystals from Belafa.
- Japan -Hiiagiyama, Ibaragi Prefecture; Ishiyamadera, Shiga Prefecture; and Kushiro, Hiroshima Prefecture
Occurrence of Wollastonite and Useful Mineral Association
Wollastonite is commonly found in thermally metamorphosed siliceous carbonates, the intruding igneous rock, and skarn deposits along their contact. It is also found in some alkalic igneous rocks and carbonatites. It is often associated with minerals such as bustamite, ferrobustamite, pectolite, sérandite, and tanohataite.
References
http://rruff.geo.arizona.edu/doclib/hom/wollastonite.pdf
http://www.mindat.org/min-4323.html
http://webmineral.com/data/Wollastonite-1A.shtml
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