Dictionary:

wollastonite

  (wʊl'ə-stə-nīt')

A white to gray mineral, essentially CaSiO₃, found in metamorphic rocks and used in ceramics, paints, plastics, and cements.

[After William Hyde WOLLASTON.]

A mineral inosilicate with composition CaSiO₃. Commonly it is massive, or in cleavable to fibrous aggregates. Hardness is 5–5½ on Mohs scale; specific gravity is 2.85. On the cleavages the luster is pearly or silky; the color is white to gray.

Wollastonite is found in large masses in the Black Forest of Germany; Brittany, France; Chiapas, Mexico; and Willsboro, New York, where it is mined as a ceramic material. See also Silicate minerals.

Environment

A mineral of contact-metamorphic deposits in limestones and in ringing intrusive stocks.

Usually in fibrous, somewhat splintery masses of elongated crystals flattened parallel to the base and to the front pinacoid, giving the impression of slender prismatic needles. Also, but infrequently, as single crystals, often coarsely granular, compact, and massive.

White to colorless, pink, or gray. Luster glassy to silky; hardness 4Ɖ-5; specific gravity 2.8-2.9; fracture splintery; cleavage perfect pinacoidal (pseudoprismatic) on base and front pinacoid at 84° and 96° to each other. Translucent; often fluorescent in yellow and orange.

Calcium silicate (48.3% CaO, 51.7% SiO ₂ ).

Fuses to a white globule. Dissolves in hydrochloric acid, with a separation of shreds of silica.

Distinguished from tremolite by greater fusibility and its cleavage angles, which are near those of the pyroxenes and far from the 56° and 124° of the amphiboles. Distinguished from diopside and prismatic topaz (pycnite) by its fusibility and solubility in acid. Fluorescence is commonly an aid to quick identification.

Common where limestones have been strongly metamorphosed, as in Llano Co., Texas, and Riverside Co. (at Crestmore) and San Diego Co., California. Good examples of distinct crystals come from Natural Bridge, St. Lawrence Co., New York. Richly fluorescent specimens were found at Franklin, New Jersey. As might be expected, crystals are found in the altered limestone blocks thrown out by the eruptions of Monte Somma on Vesuvius. Typical fibrous masses come from Perheniemi, Finland, and crystals from Banat, Romania, and in the marble of Tremorgio, Switzerland. A small amount is mined for use in ceramics.

The noun has one meaning:

Meaning #1: a white or grayish mineral typically found in metamorphic limestone; a silicate of calcium

Wollastonite
General
Category	Silicate mineral
Chemical formula	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
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).

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.

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^[1] in the linked chain (as opposed to two in the pyroxenes).

Production trends

Wollastonite output in 2005

In 2005, China was the top producer of wollastonite with atleast 50% world share followed by India and the USA, reports the British Geological Survey.

In the United States, wollastonite is mined in Willsboro, New York and Gouverneur, New York. Deposits have also been mined commercially in North Western Mexico.

See also

• List of minerals
• List of minerals named after people

References

1. ^ Deer, Howie & Zussman (1966) An Introduction to the Rock Forming Minerals, Longman 528pp + xii, ISBN 0-582-44210-9

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
• Mindat
• Webmineral
• Mineral galleries
• Oxford University MSDS sheet

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