128 



UNITED STATES MINERAL RESOURCES 



Georgia, and Mississippi are the major fuller's 

 earth-producing States. Bentonite production data 

 (fig. 14) are available for only 40 years because 

 before 1930 they were included in the miscellaneous- 

 clay category. The production data for fuller's earth 

 for the past 50 years are shown in figure 14. The 

 average value per ton of bentonite increased from 

 $5.37 in 1936 to $11.83 in 1960 and then decreased 

 to $9.82 in 1969. Some of this decrease in value 

 during the 1960's was due to the increased demand 

 for low-cost poor-quality bentonite as a bond in 

 pelletizing fine-grained iron ores. The average value 

 per ton of fuller's earth increased from $9.28 in 

 1933 to $25.77 in 1969. Part of this increase in 

 value took place in the 1960's when animal litter, 

 sold in small quantities, became popular at the 

 supermarkets. 



Much of the best grade "Wyoming" or "sodium" 

 bentonite occurs in the Mowry Shale of Cretaceous 

 age in Wyoming and South Dakota. The Clay Spur 

 Bentonite bed, near the top of this formation in a 

 belt surrounding the Black Hills, has been a major 

 source of bentonite, and it still contains large re- 

 serves. Other beds in the Mowry Shale and younger 

 formations have been mined in the vicinity of the 

 Bighorn Mountains, Wyo. and at scattered locali- 

 ties in Montana. The "calcium" or "southern" ben- 

 tonite of Cretaceous age is mined in Mississippi and 

 Alabama. Extensive beds of "calcium" bentonite of 

 Tertiary age have been the major sources of ben- 

 tonite in Texas, Arizona, and California, and smaller 

 deposits of "calcium" bentonite occur in all Western 

 States. A unique magnesium and lithium-bearing 

 high-swelling bentonite termed "hectorite" occurs 

 near Hector, Calif., and at a locality in Arizona. 

 Altered volcanic rock, consisting mainly of mont- 

 morillonite, is mined at a locality in Utah and sold 

 as bentonite. Probably similar rock in other States 

 is used as bentonite. 



Most fuller's earth deposits occur as beds in sedi- 

 mentary rock, but some are hydrothermally altered 

 volcanics. The deposits in southern Georgia and 

 northern Florida that consist mainly of palygorskite 

 and montmorillonite are in the Havi^horn Forma- 

 tion of Miocene age. Fuller's earth also occurs in 

 this formation in central peninsular Florida and in 

 the vicinity of Tampa, Fla. Significant tonnages of 

 fuller's earth products are produced from the 

 Twiggs Clay of Eocene age in middle Georgia. The 

 Porters Creek Clay of Paleocene age, which con- 

 tains enormous tonnages of fuller's earth, is mined 

 at six localities. This formation extends from south- 

 eastern Missouri to southern Illinois, across the 

 western part of Kentucky and Tennessee, across 



northeastern Mississippi, and well into Alabama. 

 The clay in both the Twiggs Clay and the Porters 

 Creek Clay consists chiefly of montmorillonite and 

 poorly crystalline silica in the form of opal or cris- 

 tobalite. Bentonite is mined at a few places in 

 Texas, California, and elsewhere and is sold as 

 fuller's earth. Altered volcanic rock consisting 

 chiefly of montmorillonite is also mined in Utah and 

 California and is sold as fuller's earth. 



Resources of all grades of both bentonite and 

 fuller's earth are very large. The reserves of ben- 

 tonite must be considered as at least 1 billion tons, 

 and any estimate of presumed resources would be 

 much greater than this figure. The estimate of 1 

 billion tons includes large deposits of bentonite 

 suitable for bonding iron-ore pellets, but it is classed 

 as submarginal for uses such as drilling mud. The 

 reserves of very high grade colloidal bentonite are 

 limited, and deposits of this type are in demand. 

 Resources of fuller's earth are tentatively estimated 

 at 2 billion tons. Almost any figure, however, could 

 be used here, if all the material equivalent to the 

 grade of fuller's earth used in the past, but now 

 considered submarginal is included. This would in- 

 clude much of the extensive Porters Creek Clay, the 

 Twiggs Clay, thick opal claystone beds, and many 

 scattered impure or low-grade bentonites. 



MISCELLANEOUS CLAY 



The term "miscellaneous clay" is used by the U.S. 

 Bureau of Mines for clays and shales that do not 

 fit any of the other five categories. The miscellaneous 

 clay and shale may be any color and may contain 

 a large amount of impurities, but the color and 

 impurities may give the clay the necessary proper- 

 ties to make the final product a salable item. Mis- 

 cellaneous clays and shales are used chiefly in mak- 

 ing fired products, but some are used in the unfired 

 form. The unfired uses are as follows: Shale for 

 filler in paint and asphalt; clay for abrasives, 

 termed "rottenstone" ; shale for "clay dummies" 

 used to pack dynamite in blasting holes; and clay 

 used for plugging oil and gas wells. These products 

 are easily processed, requiring only drying, grind- 

 ing, and bagging. Fired products made from mis- 

 cellaneous clay and shale include face and structural 

 brick, vitrified sewer pipe, drain tile, flue tile, con- 

 duits, pottery, and stoneware and floor, wall, and 

 roofing tile. In addition to these uses, clay and shale 

 are used in the manufacture of portland cement and 

 lightweight aggregate. 



The demand for miscellaneous clay has increased 



