Wollastonite

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Wollastonite
Image:WollastoniteUSGOV.jpg
General
Category	Mineral
Chemical formula (or Composition)	Calcium silicate, CaSiO₃
Identification
Color	white, colorless or gray, monoclinic
Crystal habit	rare tabular crystals - commonly massive in lamellar, radiating, compact and fibrous aggregates.
Crystal system	triclinic bar 1
Cleavage	perfect in two directions at near 90 degrees
Fracture	splintery to uneven
Mohs Scale hardness	4.8
Luster	vitreous or dull to pearly on cleavage surfaces
Refractive index	a=1.628, b=1.639, g=1.642
Pleochroism	-
Streak	White
Specific gravity	2.82
Melting point	1540 °C
Solubility	soluble in HCl, insoluble in water

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 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, and calcite. It is named after the English chemist and mineralogist William Hyde Wollaston (1766-1828).

In the United States, wollastonite is mined in Willsboro, New York. Deposits have also been mined commercially in North Western Mexico. China is the leading producing country. Some of the properties that make wollastonite so useful are its high brightness and whiteness, low moisture and oil absorption, and low volatile content. Wollastonite is used primarily in ceramics, friction products (brakes and clutches), metalmaking, paint filler, and plastics.

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