346 



UNITED STATES MINERAL RESOURCES 



pumicite is exported. Almost all the vermiculite used 

 in the United States is produced domestically, but 

 along the eastern seaboard, oceanic freight rates 

 allow some vermiculite to be imported economically 

 from the Republic of South Africa. In 1970 the 

 United States was the world's largest producer of 

 crude vermiculite, at about 285,000 tons, and South 

 Africa was second, with about 134,000 tons (Fulker- 

 son, 1972). The most lecent import data are for 

 1969, when about 6,500 tons entered the United 

 States; this was equivalent to a little more than 2 

 percent of the domestic production. 



EXPLOITATION 



The production histories of vermiculite and per- 

 lite are broadly similar in their early periods, and 

 are very closely related since about 1955 (fig. 42). 

 Vermiculite was first produced in Colorado in 1913, 



but the first significant sustained production began 

 in Montana in 1925, with about 100 tons of crude 

 ore. The growth rate was rapid, but the tonnages 

 were small to 1937 (about 27,000 tons in 1937). 

 The rate then became more gradual, but tonnage 

 increased to about 200,000 tons in 1950, and then 

 growth was slow but steady to about 300,000 tons 

 in 1969 and 1970. Perlite production began after 

 World War II and about 5,000 tons of crude ore was 

 produced in 1946; output rose rapidly to about 

 150,000 tons in 1951, and growth has continued at 

 a slower but steady rate to more than 450,000 tons 

 in 1969 and 1970. Since 1955 the annual increases 

 and decreases in production of crude vermiculite and 

 crude perlite virtually parallel each other, with the 

 production of perlite about 150,000 tons greater 

 than that of vermiculite. Consumption of expanded 

 perlite has varied more than that of exfoliated ver- 



900 

 800 



400 

 300 



O 90 



S 80 



"" 70 



O 60 



D 30 



Q5 



zi- 



FiGUKE 42. — Production of materials used as ultralightweight aggregates in the United States, 1935-70; U.S. Bureau of 



Mines Minerals Yearbooks. 

 New construction. — Value of total new construction, exclusive of maintenance and repair; data from Statistical Abstracts 



of the United States, 1935-70. 

 Perlite, crude. — Total crude ore sold and used by producers. 

 Perlite, expanded. — Total produced. 



Vermiculite, crude — Total crude ore sold and used by producers. 

 Vermiculite, exfoliated. — Total produced. 



