CLAYS 



129 



in the United States so that in 1969, 42.3 million 

 short tons, valued at $63.3 million, of miscellaneous 

 clay and shale was produced. Every State, except 

 Alaska and Rhode Island, has produced miscellan- 

 eous clay products. The States producing over 1 

 million tons in 1969 were Alabama, California, 

 Georgia, Illinois, Indiana, Iowa, Kentucky, Mary- 

 land, Michigan, Mississippi, Missouri, New York, 

 North Carolina, Ohio, Pennsylvania, South Caro- 

 lina, Tennessee, Texas, and Virginia. Miscellan- 

 eous clay production increased tremendously in 

 the 1944-46 period (fig. 14) because there was 

 an increase in building construction following 

 World War II. Before that time, clay production 

 fluctuated considerably, but since then production 

 has been steady. The average value per ton of mis- 

 cellaneous clay was lowest at $0.72 in 1944 and 

 highest at $2.91 in 1929, just before the depression. 

 The average value per ton in 1969 was $1.49. 



Miscellaneous clay and shale occur in rocks rang- 

 ing in age from Precambrian to Holocene and are 

 formed by several different geologic processes. Rocks 

 used for miscellaneous clay products include both 

 fresh and weathered shale, weathered and fresh 

 schist, slope wash and alluvium, loess, and ferru- 

 ginous saprolite. Underclay beds and kaolin are also 

 used in heavy-clay products, and some production of 

 these clays is reported as miscellaneous clay by the 

 U.S. Bureau of Mines. 



Reserves of miscellaneous clay and shale are 

 enormous in many areas of the United States, but 

 a few plants in or near metropolitan areas have 

 raw-material-supply and air-pollution problems. 

 The suburban spread of large cities, especially on 

 the east coast, has engulfed a few brick and tile 

 plants and their clay and shale resources. Some 

 plants must be relocated or face increasing costs of 

 transporting raw material, and other plants will 

 have to install smoke and dust clarifiers. Future de- 

 mands for products made from miscellaneous clay 

 and shale can be expected to increase at the same 

 rate as demands for the past two decades ( fig. 14). 

 The demand for structural clay products should 

 continue to grow, although competition from other 

 building materials will also continue to increase. 

 The demand for shale in making lightweight aggre- 

 gate continues to increase and may replace much of 

 the sand and gravel which are being depleted near 

 some of the large eastern cities. 



Resources of miscellaneous clay and shale are vir- 

 tually inexhaustible. The average value per ton is 

 so low that the economics of land values, mining 

 costs, production problems, transportation, market 

 demands, and competition are much more important. 



SUMMARY OF RESOURCES 



A summary of the resources of the various types 

 of clays is given in table 25. 



Table 25. — Summary of clay resources of the United States 



1 Reserves: Identified deposits from which minerals can be extracted 

 profitably with existing technology and under present economic conditions. 



- Potential resources : Identified mineral deposits not profitably recover- 

 able with existing technology and economic conditions and undiscovered 

 mineral deposits whether of recoverable or subeconomic grade. 



ENVIRONMENTAL CONSIDERATIONS 



Almost all clay deposits are mined from open pits ; 

 heavy equipment is used to remove the overburden 

 and dig the clay. Surface mining destroys the beauty 

 of the countryside and may pollute streams and 

 rivers. Most States require clay producers to install 

 settling ponds to prevent contaminiation of the 

 streams; some States require open pits to be back- 

 filled and covered with vegetation to restore the 

 mined-out areas. Many older abandoned pits are, 

 however, ugly scars detracting from the beauty of 

 the countryside. Many clay-processing plants have 

 installed, and others will be required to install, 

 smoke- and dust-control systems to prevent atmos- 

 pheric pollution. This, along with increased mining 

 costs, will raise the future market prices of manu- 

 factured clay products. 



PROBLEMS FOR RESEARCH 



More geologic studies are needed related to clay 

 deposits, especially bentonite and fuller's earth, and 



