PIGMENTS AND FILLERS 



535 



I 



WOLLASTONITE 



Wollastonite (CaSiOs) an acicular white mineral, 

 is used mainly for wall tile and other ceramic prod- 

 ucts. It is an excellent ceramic material in that it 

 can be fired rapidly because no HuO or CO2 must be 

 driven off. The resulting ceramic does not absorb 

 water and is resistant to thermal shock and brittle- 

 ness. Although wollastonite is mainly used by the 

 ceramic industry, its use as a filler is becoming 

 much more common. The finished filler is brilliantly 

 white, fibrous, and an excellent paint extender be- 

 cause its fibrous character suspends the pigment 

 and prevents the accumulation of hard sediment in 

 the paint can. Wollastonite also forms a strong paint 

 film that weathers well. The filler is chemically 

 stable, and suspensions of wollastonite are alkaline 

 with a pH of about 10 (Andrews, 1970) . This alka- 

 linity has an advantage in paints like polyvinyl 

 acetate that decompose in time, forming acetic acid. 

 The alkaline suspension neutralizes the acid and 

 prevents corrosion of the paint can. 



The rubber industry uses wollastonite as a semi- 

 reinforcing filler in nonblack rubber goods. The 

 plastics industry uses it in thermosetting and ther- 

 moplastic casein resins and in asphalt and vinyl 

 floor tiles. Wollastonite filler has high opacity and 

 has been experimented with as a filler and coater 

 for paper. For these uses, however, it apparently 

 cannot compete with kaolin, which is less expensive. 



Most wollastonite is found in contact metamorphic 

 zones between calcareous and intrusive rocks. In the 

 United States it was mined for mineral wool as 

 early as the 1930's from a small deposit in Kern 

 County, Calif. A much larger deposit at Willsboro, 

 N.Y., along the contact of the anorthosite mass in 

 the northeastern part of the Adirondack Mountains, 

 was developed in the early 1950's, and material 

 mined from there since 1953 is used in an ever- 

 increasing number of products. Total world pro- 

 duction of wollastonite has been not over 50,000 

 tons, and four-fifths of this has come from the New 

 York deposit. The other principal producers are 

 Mexico and Finland. Andrews (1970) has a com- 

 plete and comprehensive report on wollastonite, its 

 uses, and resources throughout the world. The peri- 

 odical "Industrial Minerals" (1969b, and Whitmer, 

 1969) also presented a thorough study of wollas- 

 tonite. 



Although most of the U.S. production of wollas- 

 tonite is from the deposit in New York, the mineral 

 is still mined in Riverside County, Calif., where 

 recovery is mainly for decorative stone. In 1966, 

 however, some mining for industrial wollastonite 

 was begun from the California deposits, but pro- 



duction since then apparently has been small. 



Arizona, Nevada, Utah, and the Virgin Islands 

 are also cited by Andrews (1970) as containing 

 notable occurrences of wollastonite. 



World identified resources of wollastonite amount 

 to more than 60 million tons, and hypothetical re- 

 sources are three times that according to Andrews 

 (1970, p. 2). An appraisal of resources by nations 

 has not been made. 



MISCELLANEOUS FILLERS 



Several other minerals and rocks such as Port- 

 land cement, gypsum, rock dust, ground slate, and 

 phosphorite are locally and occasionally used as 

 fillers. A small quantity of feldspar also has been 

 used in the past few years as an extender in paint 

 and a filler in rubber. 



OUTLOOK FOR FILLERS 



The market for mineral fillers is intimately de- 

 pendent on the needs of a complex industrial society. 

 The demand has steadily grown and should continue 

 as a result of expansion of paper, plastics, paint, 

 rubber, and other industries. No great spurts have 

 occurred in the consumption of any one filler, and 

 in fact consumption of some has declined ; neverthe- 

 less, the overall demand has continued with many 

 small advances as new products and uses are devised. 

 This steady growth in demand will undoubtedly 

 continue in the United States. Because industries 

 requiring fillers generally seek a local source for 

 filler material to avoid high transportation costs, 

 any light-colored inert rocks with low-cost trans- 

 portation to industrial areas should be evaluated 

 for their potential use as a filler to help satisfy 

 this expanding demand. 



SELECTED REFERENCES 



American Paint Journal, 1970, Micaceous iron oxide: Am. 



Paint Jour., v. 54, June 22, 1970, p. 68-81. 

 Andrews, R. W., 1970, Wollastonite: London, Inst. Geol. Sci., 



114 p. 

 Chalk, Raymond, and Harris, G. R., 1968, Pulp and paper 



process minerals : Canadian Inst. Mining and Metallurgy 



Bull., V. 61, no. 680, p. 1427-1437. 

 Cummins, A. B., 1960, Mineral fillers, in Industrial minerals 



and rocks, 3d ed: New York, Am. Inst. Mining, Metall., 



and Petroleum Engineers, p. 567-584. 

 Fisher, W. L., 1965, Rock and mineral resources of East 



Texas: Bur. Econ. Geology, Texas Univ. Rept. Inv., 54, 



p. 287-294. 

 Fisher, F. L., 1969, Iron oxide pigments, in Minerals year- 

 book, 1969: U.S. Bur. Mines, p. 613-616. 

 Huber Corporation, 1955, Kaolin clays and their industrial 



uses: New York, J. M. Huber Corp., 214 p. 

 Industrial Minerals, 1968, Talc-mineral with a multitude of 



uses: London, Indus. Minerals, no. 5, February, p. 9-16. 



