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Talc is a hydrated magnesium silicate produced by the metamorphosis of dolomite and quartzose rocks or by the hydrothermal alteration of ultramafic and mafic rocks. As the changes are rarely complete and uniform, the rocks usually contain one or more other minerals. In pure form it is the softest of minerals. Talc is an extremely useful and economically important mineral and is, like most materials, hazardous to a degree.
This paper takes the position that talc is a victim. It is a victim of the imprecision of mineral terminology, which does not distinguish between the fibrous and nonfibrous varieties of several amphiboles. It is a victim of the terminology of its own industry, which sold “fibrous talc” for many years. It is victimized because precursor minerals in fibrous habit produce pseudomorphic talc fibers. Those same fibers are sometimes unaltered and present in talc in just enough quantity to give a near truth to claims that talc contains asbestos. Talc is a victim of monitoring methods that are totally nonspecific and call each elongate particle of whatever origin a fiber and, by analogy, asbestos. Most especially, talc is a victim of imprecise asbestos definitions, which allow the inclusion of most amphibole particles of some elongation in those definitions.
health-related silicates, talc, asbestos, definitions
Physical scientist, U.S. Bureau of Mines, Washington, D.C.