CLAYS 



127 



will probably continue to decrease in the future. The 

 major fire-clay-producing States are Alabama, Cali- 

 fornia, Colorado, Illinois, Kentucky, Missouri, Ohio, 

 Pennsylvania, Texas, and West Virginia. The minor 

 producers are Arizona, Arkansas, Idaho, Indiana, 

 Kansas, Maryland, Minnesota, Mississippi, New 

 Jersey, New Mexico, Oklahoma, Oregon, Utah, 

 and Washington. The average value per ton was a 

 low of $2.35 in 1942 and a high of $5.29 in 1967. 



All deposits of fire clay are found in sedimentary 

 rocks, and many of them are associated with coal 

 beds. Much of the fire clay produced east of the 

 Mississippi River is from the Lower Pennsylvanian 

 sedimentary rocks; these clays are referred to as 

 underclays because they almost invariably occur 

 just below coal beds. Some kaolin called fire clay is 

 mined from the Raritan Formation of Cretaceous 

 age in New Jersey, from the Nanafalia Formation 

 of Eocene age in Georgia and Alabama. West of 

 the Mississippi River, fire clay occurs in beds and 

 lenses of the Dakota Sandstone of Cretaceous age 

 in at least six States. In Missouri, the clay is in the 

 Cheltenham Clay of Wanless (1939) of Pennsyl- 

 vanian age. In the Pacific Coast States and Idaho, 

 fire clay occurs in Eocene sediments, the lone For- 

 mation in California being the most productive. 



The reserves of fire clay suitable for use in low- 

 and moderate-heat-duty refractories are estimated 

 at 1 billion tons, and for high-heat-duty refractories, 

 flint and nodular flint clays, the reserves are esti- 

 mated at about 500 million tons. Resources of fire 

 clay are estimated at approximately 7 billion tons. 

 If the future demands for fire clay decrease, the 

 present production trend of fire clay will continue 

 as shown (fig. 14) ; however, most of the decline 

 will be in the demand for high-heat-duty refractory 

 products, and the demand for low- and moderate- 

 heat-duty refractory products will remain constant 

 and may increase in the future as the production of 

 metals expands. 



In some areas where fire clay occurs as underclay, 

 there is economic waste in the mining methods. 

 Before World War II, almost all fire clay was mined 

 by underground methods, and the coal was left be- 

 cause it made a better, safer roof than shale. Local- 

 ally, the coal was mined from areas in the mine 

 where the clay had been removed previously. Under- 

 ground mining has become very costly, and for the 

 past 10 years, fire clay has been almost exclusively 

 strip mined. Now, the clay companies rarely mine 

 any potentially economical coal as a coproduct, and 

 the coal is wastefully placed on the spoil bank with 

 the overburden by means of draglines, power shov- 

 els, and bulldozers. 



BENTONITE AND FULLER'S EARTH 



Bentonite and fuller's earth are clay commodities 

 that are related either by mineral composition or 

 by use. The term "fuller's earth" comes from its 

 former use which was for cleaning or fulling wool 

 by fullers. Both bentonite and fuller's earth have a 

 wide variety of physical properties that make them 

 suitable for many different uses and applications. 

 Both are used in drilling muds, bentonite principally 

 where fresh water is present in the rocks penetrated 

 and palygorskite-type fuller's earth where salt 

 water is present. The "sodium," "high swelling," or 

 "Wyoming"-type bentonite has exchangeable sodium 

 ions and when wetted with water will increase in 

 volume 15-20 times. The "calcium," "low-swelling," 

 or "southern" bentonite will not increase in volume 

 when wetted with water. The swelling bentonite has 

 excellent dry properties and is used for bonding 

 foundry sand and iron-ore pellets. Most of the non- 

 swelling bentonite has very good green-bond prop- 

 erties and is used in foundries employing the green- 

 mold technique. Bentonite is also used in petroleum 

 refining as a catalyst, and fuller's earth is sold for 

 clarifying and processing mineral and vegetable 

 oils. Some bentonite or fuller's earth is treated or 

 "activated" with acid to improve its effectiveness 

 in processing oil, and the activated clay is usually 

 referred to as bleaching clay. A fuller's earth prod- 

 uct termed "absorbent granules" is used for many 

 purposes, such as an agent for absorbing oil, grease, 

 and chemicals from floors, as an animal litter, and 

 as a soil conditioner. Both fuller's earth and ben- 

 tonite are used as carriers for insecticides and 

 fungicides, and minor quantities of bentonite are 

 sold for many other uses, such as sealing irrigation 

 canals and reservoirs. 



The first shipment of bentonite for commercial 

 purposes was made in 1888 from Rock Creek, Wyo., 

 by William Taylor. Fuller's earth was first pro- 

 duced in the United States in 1891, when a bed of 

 Tertiary clayey marl near Alexander, Ark., was 

 mined. This clay, however, was used for only a very 

 short time because it proved to be unsatisfactory. 

 In 1893, fuller's earth was discovered through curi- 

 osity near Quincy, Fla., when an effort to burn 

 brick proved unsuccessful. The production of both 

 bentonite and fuller's earth has increased more or 

 less steadily since the late 19th century. In 1969 

 the production of bentonite reached 2.6 million short 

 tons valued at $25.9 million, and the production of 

 fuller's earth reached 984,000 short tons valued at 

 $25.3 million. Wyoming, Mississippi, and Texas are 

 the major bentonite-producing States, and Florida, 



