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1916414 
Technical Report 
A Definition for Talc 
Ross, M 
1984 
NIOSH/00174559 
Related Silcates 
193-197 
A definition for talc (14807966) was presented, based on discussions held during a workshop on the subject. Talc was described as a naturally occurring single phase mineral ideally composed of 31.88 percent magnesium-oxide, 63.37 percent silicon-dioxide, and 4.75 percent water. Formation was said to occur by hydrothermal alteration of rocks rich in magnesium and iron and by low grade thermal metamorphism of siliceous dolomites. Relatively little chemical variation was found, and chemical and ion composition of five samples from different continents were tabulated. The crystal structure was described as a layer of magnesium-oxide sandwiched between layers of silicate. Small amounts of aluminum have been found to be able to substitute for silicon in the crystal structure, and small to moderate amounts of aluminum, iron, and manganese for magnesium. Naturally occurring talcs were also found possibly to contain small amounts of fluorine, titanium-dioxide, calcium-oxide, and sodium-monoxide, and nickel was found to be an essential constituent of some talcs. Characteristic physical properties of talc were presented, including crystallographic properties, optical properties, and morphology.