620 



UNITED STATES MINERAL RESOURCES 



(1963), and a map locating all talc-mining areas was 

 published by Chidester and Worthington (1962) . 



MINERALOGY AND PHYSICAL PROPERTIES 



Talc is a hydrous magnesium silicate mineral with 

 the theoretical foiTnula H2Mg3(Si03)4. As used in- 

 dustrially, however, the term "talc" refers to a rock 

 composed mainly of magnesium-rich silicate min- 

 erals and having the mineral talc as an important 

 constituent. Mineral content of industrial talc can 

 range from pure talc to predominantly tremolite. 



Minerals other than talc that are most com- 

 monly present in industrial talcs are serpentine 

 (H4Mg3Si09), chlorite (hydrous Mg-Fe-Al silicate), 

 tremolite (Ca2Mg5H2(Si03)s), anthophyllite 

 ((Mg,Fe)r(OH),Sis022), and diopside (CaMg 

 (8163)2) ; less commonly present are quartz (Si02), 

 calcite (CaC03), dolomite (CaMg(C03)2), and mag- 

 nesite (MgCOa). Pyrophyllite, an aluminum silicate 

 (Al2Si,Oio(OH)2) closely related to talc in structure, 

 properties, and uses, is generally lumped with talc 

 and soapstone in production and consumption statis- 

 tics, but it is not included in this discussion. 



The constituents of industrial talc differ consid- 

 erably in physical and mineralogic properties, con- 

 sequently, rocks having different mineral propor- 

 tions vary accordingly in their properties. The 

 mineral talc is extremely soft and slippery, having 

 a hardness of 1 on the Mohs scale; and because of 

 a strong basal cleavage, it is flaky. The associated 

 tremolite and anthophyllite have a hardness of 5 

 to 6 and when ground produce a fibrous powder 

 because of their prismatic cleavage. Other minerals, 

 such as serpentine, vary in hardness and in shape 

 of pulverized particles. Most of the major constitu- 

 ent minerals of industrial talc are chemically inert 

 and generally grind to a white powder and have 

 high dielectric constants, therefore, these minerals 

 naturally occuring in varying proportions produce 

 inert light-colored rocks with a range of hardness 

 and particle shape when pulverized, making indus- 

 trial talc an unusually versatile and widely used 

 mineral product. 



USES 



Industrial talc is used where certain combinations 

 of the following properties are desired: Extreme 

 whiteness when powdered or fired, softness or 

 smoothness, fibrous or flaky particle shape, various 

 degrees of oil absorption, chemical inertness, high 

 fusion point, low water absorption and shrinkage 

 when fired as a ceramic body, low electrical and 

 thermal conductivity, good retention as fillers, and 



ease of grinding to extreme fineness (Industrial 

 Minerals, 1968). 



Talc in the form of soapstone has been used since 

 prehistoric times for carved cooking utensils; cur- 

 rent uses of talc are intimately tied to the demands 

 of a complex industrial society. It is important to 

 the manufacturing and building industries, and 

 periodic fluctuations in consumption are directly 

 related to the economic conditions of those indus- 

 tries. 



Talc is used as a ceramic base material for wall 

 and floor tile; as a filler by the plastic, paper, roof- 

 ing, and rubber, industries ; as a paint extender ; and 

 as an insecticide diluent and carrier. Other special 

 uses are diverse, ranging from a polish for rice, 

 wood turnings, nails, and white shoes to a dusting 

 powder for salami. In the massive form of soap- 

 stone, it is cut for laboratory table tops and sinks, 

 steel-marking crayons, and blocks for art carvings. 

 High-frequency ceramic insulator shapes are ma- 

 chined and fired from another massive variety 

 known as block steatite, and block talc is machined 

 and fired for burner nozzles. Talc and soapstone 

 sold or used in the United States in 1969 and 1970 

 are listed by use in table 128. Figure 69 shows con- 



Table 128. — Talc and soapstone sold or used by producers in 



the United States, by uses 



[In short tons. From Wells (1970)] 



Use 1969 19T0 



Ceramics 245,704 228,595 



Insecticides 53,722 33,697 



Paint 166,170 154,265 



Paper 54,554 52,328 



Roofing 30,526 44,997 



Rubber 24,464 28,348 



Textile 7,974 6,187 



Toilet preparations 12,235 13,721 



Other' 279,168 289,644 



Total 874,517 851,782 



^ Includes asphalt fiUer, crayons, exports, fertilizer, floor and wall tile, 

 foundry facings, insulated wire and cable, joint cement, plastics, rice 

 polishing, and miscellaneous products. 



sumption of talc by the major consuming industries 

 during 1950-70. Talc used for ceramic wall tiles 

 and extender in paint now accounts for half of the 

 annual consumption. The roofing, paper, insecticide, 

 and rubber industries together consume an addi- 

 tional quarter, and the many miscellaneous special 

 uses account for the remainder. The only recent 

 outstanding increase in the consumption of talc is 

 in the "other uses" category in figure 69. This curve 

 since 1966 shows an exponential growth which I 

 attribute to the use of talc as a filler pigment in 

 white plastic insulation, containers, and sheeting. 



