Tremolitic talc

Talc of metasedimentary origin is formed by hydrothermal alteration of a dolomitic host rock by a silica-containing fluid. This type of deposit is typical of Montana and AustraUa. It is usually quite pure with talc content of 90 to 98% and often very white as well. Dolomite [17069-72-6], CaMg(C02)2, is the most common accessory mineral. The fourth type is of metamorphic origin, where a siUcaceous dolostone is first converted to tremolite [14567-73-8] or actinohte [13768-00-8] and then partially converted to talc. The Balmat, New York, and Death Valley, California, deposits are of this type. Tremolite, dolomite, and serpentine are common accessory minerals. This type of talc deposit has a variable talc content (30—80%), but is usually white and often commercially exploited because of the properties of its accessory minerals rather than the talc. 

Ceramics. In ceramics, talc is widely used in wall tile and hobbyware bodies, in electrical porcelains, and in cordierite formulations. Wall tile and hobbyware ate talc—clay bodies that ate pressed and fast-fired to a high porosity (bisque) and then glazed and tefired to produce the final product. Talc containing tremolite and carbonate is preferred to ensure good porosity. 

Hydrothermal alteration minerals from midoceanic basalt are analcite, stilbite, heulandite, natrolite-mesolite-scolecite series, chlorite and smectite for zeolite facies, prehnite, chlorite, calcite and epidote for prehnite-pumpellyite facies, albite, actinolite, chlorite, epidote, quartz, sphene, hornblende, tremolite, talc, magnetite, and nontronite for green schist facies, hornblende, plagioclase, actinolite, leucoxene, quartz, chlorite, apatite, biotite, epidote, magnetite and sphene for amphibolite facies (Humphris and Thompson, 1978). 

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... 

Although there are a number of contradictory reports regarding the effects of talc, the contradiction has been ascribed to the differences in mineral composition of the various talcs, which include pure talc, talc associated with silica and other nonasbestiform minerals, and talc containing asbestiform fibers such as tremolite and anthophyllite. ... 

A study of 260 workers with 15 or more years of exposure to commercial talc dust (containing not only talc, but also tremolite, antho-phyllite, carbonate dusts, and a small amount of free silica) revealed a 40-fold greater than expected proportional mortality from cancer of the lungs and pleura. In addition, a major cause of death was cor pulmonale, a result of the pneumoconiosis the effects were likely due to the asbestos-form contaminants. The role of nonfibrous talc in these disease states could not be assessed. 

Talc fibers may be present in some talcs, especially if the talcs contain anthophyllite or tremolite asbestos and a metamorphosis or transition to talc has taken place. The transition is sometimes incomplete as in talcs from the Gouveneur district of upper New York State. If talc fibers are present, further testing as described below will be necessary. 

If asbestos is present and the sample is not a talc sample, it is most likely to be chrysotile since about 90% or more of the asbestos used in American industry is chrysotile. If the sample is taken from a shipyard, there is a high probability that it will be amosite asbestos. If asbestos is found in a talc sample, it is likely to be anthophyllite or tremolite-actinolite or an asbestos intermediate fiber chrysotile is a possibility, however. If the sample is insulation, expect a variety of fibers. 

Tremolite and anthophylUte can be identified in 1.620 medium. In a talc sample where talc fibers may also be present, 1.605 medium is prefered. This will distinguish between talc fibers and asbesestos fibers by the dispersion staining colors. 1.605 medium will also distinguish between wollastonite and asbestos. 

Another common alteration involves the replacement of serpentine by chlorite, resulting in a rock composed solely of chlorite and magnetite. Further replacement by talc or talc-carbonate will result in a talc-chlorite (-carbonate) soapstone. Other alterations can result in the formation of tremolite-talc or chlorite-tremolite-talc soapstones. 

The original serpentinite was altered to antigorite- dolomite, talc, and tremolite, and the hornblende diorite (H,D ) was altered to chlorite with some tremolite. The numbers refer to samples taken along the alteration zone (the distance between samples 1 and 5 was about 2 ft), and the concentration of the Cr (M), Eu (i, or Sm ( ) in each sample is shown normalized to the levels found in unmetamorphosed serpentinite. The theoretical concentration profile for Sm is shown by the dashed line and was calculated assuming similar partition coefficients (mineral/solution) for all of the minerals formed from the serpentinite. 

Two important factors are suggested by this model. First, the concentration of a trace element in a particular mineral (like talc) formed in this manner depends upon many factors including the size and charge of the ion (which eflFect the partition coefficient), the composition of the aqueous solution, the minerals present in the intrusive (determines D ), and the time or extent of reaction. Since talcose rocks of similar composition can be formed by various different processes, the differences in any of the factors noted above would result in different trace element contents. Second, since the assumption that the partition coefficients for antigorite, talc, and tremolite are similar appears to be true, one would expect their trace element contents to be similar. This means that a series of soapstone samples collected from a particular geologic body might contain different amounts of these minerals but that they all would probably be very similar in trace element content despite differences in the bulk element composition of the samples. 

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