Massive talc

SYNONYMS massive talc, silicates soapstone (ACGIH OSHA), soapstone silicate, steatite. 

Synonyms/Trade Names Massive talc. Soapstone silicate. Steatite... 

Soapstone, a mineral name applied to steatite or massive talc... 

An important specialized utilization of porcelain is in electrical porcelain, as in, e.g., electrical insulators. Here high dielectric strength, which is concomitant with low porosity, is an important property of electrical porcelain. Steatite (soapstone, a massive talc-rich rock) can also be an ingredient in (especially low tension) electrical porcelain. 

Talc, unlike Che micas, consists of electrically neutral layers without the interleaving cations. It is valued for its softness, smoothrtess and dry lubricating properties, and for its whitertess, chermcal inertness and foliated structure. Its most important abdications are in ceramics, insecticides, paints and paper manufacture. The more familiar use in cosmetics and toilet preparations accounts for only 3% of world production which is about 5 Mt per annum. Half of this comes from Japan and the USA. and other major producers are Korea, the former Soviet Union, France and China. Talc and its more massive mineral form soapstone or steatite arc widely distributed throughout the world and many countries produce it for domestic consumption either by open-cast or underground mining. 

The Arnold Pit is on the steeply dipping, overturned limb of the Sylvia Lake Syncline, the structural hanging wall is the stratigraphic footwall. Commercial talc occurs in Unit 13 near the contact with Unit 14 of the Upper Marble from the metamorphism or impure evaporative dolomite. The upper section of Unit 13 grades from tremolite-rich talc ore into a pure talc schist up section. Unit 12 is a white massive doiomitic marble with convolute bands of grey and orange to... 

Soapstone or steatite are names generally applied to any soft, waxy or greasy, massive metamorphic rock. The dominant mineral is usually talc, a light-colored magnesium silicate. Other phyllosilicate minerals or mixtures of minerals are used in similar ways, since their relative softness makes them attractive to carvers. Massive soft soapstone has also been used to make sinks, electrical switchboards, and ovens. 

Retinal neovascularization as a consequence of talc injection can occur in the retinal periphery as neovascu-lar tufts in the shape of sea fens at the junction of the perfused and nonperfused retina.This is a potentially serious complication of talc emboli, because it can lead to retinal detachment, massive vitreal hemorrhage, and optic disc neovascularization. 

In nature, it occurs in crystalline or massive varieties. The former are more distinctly laminar and cleavable. During ceramic processing, they exhibit a certain plasticity, but at the same time show a tendency to preferential orientation of flakes which results in non-uniform firing shrinkage and subsequent formation of harmful stresses. The massive varieties (called steatite or block talc) do not have this disadvantage. 

Mg3Si4O10(OH)2or3MgO 4SiO2 H2O. A natural hydrous magnesium silicate. Compact, massive varieties may be called steatite in distinction from the foliated varieties, which are called talc. Soapstone is an impure variety of steatite. 

Steatite is mineralogically the same as talc, also known as soapstone or French chalk the term steatite, however, is usually reserved for the massive form. 

Like the montmorillonites, talc cleaves easily along one plane it is soft and has a characteristic soapy feel. In the massive block form it can be readily machined, and fired to produce a strong body. Unlike the montmorillonites it is not plastic and so clay is sometimes added as a binder. 

Geologically, talc is typically formed by the alteration of a dolomite or serpentin-ite host rock. The talc formed from a dolomite host is typical of the type found in Montana, France, and China. These massive deposits are characterized by a microcrystalline talc structure, with talc concentrations in the deposit ranging from 93% to 99% talc by weight. Talc from these deposits can be sorted manually, optically, or mechanically to enhance color and talc content. 

Rare tabular pseudohexagonal crystals have been found, but talc is usually very fine grained and massive. 

Ceramic processing occurs through some sequential activities, which starts with raw materials, proceeds through batch preparation and forming and concludes with firing. The sequence of steps is illustrated by Fig. 8.7. Ceramics are formed from raw materials used for traditional ceramics which are different from those used for advanced ceramics. For traditional ceramics raw materials consist of silica, clay, fluxes and are refractory materials. Silica is obtained either from massive quartz deposit or pure quartz sands. The quartz is washed and groimd. The most commonly used clay minerals are kaolin and talc. China clay is predominantly kaolin. Ball clays are finer particle size elays that contain... 

Steatite. Massive form of the mineral talc, Mg3Si40io(OH)2. The chief sources are in USA, France, Italy, India, Austria and Norway. The natural rock can be machined and the shaped parts fired for use as electroceramics. A far greater proportion is ground and shaped in the usual way with a clay bond to produce low-loss electroceramics thermal expansion (20-500°C) 7-9 x 1(H volume resistivity (300°C) 10 - 10 ohm-cm. dielectric constant (1 MHz) S.5-6.5 power factor (IMHz) 5 - 25 x ICH. Steatite is also used as a raw material for cordierite electroceramics and for refractories containing cordierite. Steelite. A high strength hotelware body, presumed to contain alumina, first introduced by Ridgeway Potteries, 1967. Now the name of a hotelware company, Steelite International Ltd, Stoke-on-Trent. 

Processable talc deposits are widespread, although not as extensive as those of calcium carbonate or clay, with main production coming from north-east, south and west USA, Norway, France, Italy, India, China and Australia. Some massive forms, known as steatite or soapstone (after the characteristic soapy feel of talc) occur, but most of the talc is found in veins. 

TALC. 3Mg0-4Si02-H20. Talc is a hydrous magnesium silicate, with the composition 63.4% SiOj, 31.9% MgO and 4.7% HjO when found in pure form. It is an extremely soft mineral with a Mohs hardness of 1, has a platy structure and it is naturally hydro-phobic. Talc occurs as a relatively pure massive mineral in Montana, Australia and China. Elsewhere it occurs in conjunction with magnesite (Vermont, Quebec, Ontario and Finland), with tremoUte and serpentine in New York and with chlorite in France and Austria. In many ceramic applications, the presence of non-talc minerals such as chlorite and tremolite are beneficial. 

Talc used in ceramics is usually mined, sorted, crushed, and milled to 95-99% -200 mesh. MiUing is done in roUer mills for softer massive ores while ball mills are used for harder tremohtic products. Products are shipped as a dry powder, mostly in 50 pound bags but the use of supersacks is increasing and larger customers use bulk rail or truck. Some product is calcined prior to shipping and this wiU usually improve dry pressing characteristics. 

The various talcs can result in several distinctive radiographic appearances. The nodular pattern consists either of opacities some 3-5 mm in diameter, identical to those of silicosis, or of appearances similar to mixed dust fibrosis . These changes sometimes favor the middle lung fields but may be distributed throughout all zones (Fig. 12.8a). There are large opacities similar to those of silicotic conglomerations or coal progressive massive fibrosis, which may show evidence of cavity formation (Jones et al. 1994) (Fig. 12.9a). 

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