Wollastonite

WOLLASTONITE (from the name of the English naturalist William Hyde Wollaston * EN: wollastonite, tabular spar; DE: Wollastonit; FR: wollastonite; ES: wollastonita; RU: волластонит) is the mineral of the subclass of the chained silicates, Ca3[Si3O9]. The wollastonite often contains the admixtures of Fe (up to 9.3% of the FeO within the ferrowollastonite), Mn (up to 5.5% of the MnO), partly the MgO (up to 0.6%).

The wollastonite is the triclinic modification of the low-temperature form of the CaSiO3; they distinguish the wollastonite from the rare and similar monoclinic modification, namely, parawollastonite, according to the X-ray diffraction analysis and optical orientation. The high-temperature form CaSiO3, namely, the triclinic pseudowollastonite, is stable at the temperature of above 1120±10 degrees Celsius, and is extremely rare within the nature. The major motive of the crystal structure of the wollastonite is the chains of the [SiO4]-tetrahedra, which are joined with the columns of the CaO6-octahedra.

The wollastonite forms mostly the columnar, sheaf-like, fibrous, less often the foliated and shelly aggregates, the crystals of the acicular or tabular habit. The colour of the wollastonite is brown, gray, sometimes colourless, less often yellowish, greenish, brownish, reddish (because of the admixture of iron). The lustre is vitreous to pearly, the lustre of the fibrous masses is silky. The wollastonite is usually opaque, but rarely there may be encountered the transparent varieties. The cleavage is perfect along one direction, and the cleavage is good along other two directions. The wollastonite is brittle. The hardness is 5-5.5. The density is 2900-3000 kilograms per cubic metre.

The wollastonite is the rock-forming mineral of the thermally metamorphosed limestones and marbles with the admixture of the silica or silicates; the wollastonite may be encountered within the skarns, contact hornfels (skarnoids), less often within the regionally metamorphosed rocks (where, however, it forms the largest clusters), and also within the complexes of the ultrabasic - alkaline rocks and carbonatites. The largest deposit of the wollastonite within the world, namely, the Willsboro (the Adirondack Mountains within the New York state, USA), with the proven reserves of 5.4 million tonnes of the ore, is associated with the regional metamorphism; other deposits of this type are known within the USSR and India. Within the USSR, there have the practical significance mainly the deposits of the skarn type: Langar, Koytash (Middle Asia), Slyudyanskoe (Irkutsk province), Bosaga (Kazakh SSR), and others.

The worldwide extraction of the wollastonite is 127 thousand tonnes (1978). The major consumer is the USA (63 thousand tonnes). The wollastonite is one of the prospective types of the raw materials for the electroceramics (the insulators with the extremely low dielectric losses), for the special high-frequency radioceramics, for the wall slabs, for the facing bricks and tiles, for the glazed tiles, for the special cements, whitewashes, paints, lacquers, glazes, and enamels with the increased strength and water resistance, for the white mineral wool, for the absorbents, for the special filters, for the fertilizers, and so on. The wollastonite is used as the filler within the glass industry and paper industry, is added to the asbestos, and to the asphalt mass (for the slabs), and so on. The major method for the beneficiation is the flotation. The collectors are: the emulsion of the tall oil within the kerosene, the liquid soap, the alkyl sulfate, the resin-acidic laurylamine. Preliminarily, there is extracted from the ore the calcium. There is also used the collective flotation of the calcite and wollastonite, with the subsequent selection of the collective concentrate, using the depression of the wollastonite, using the liquid glass. The refinement of the concentrate of the wollastonite is performed using the removal of the heavy dark-coloured minerals on the concentration tables.