126 



UNITED STATES MINERAL RESOURCES 



Byproducts — sand for use in making glass and 

 muscovite for use in insulation and other prod- 

 ucts — are recovered from kaolin deposits in Latah 

 County, Idaho, and muscovite is recovered near 

 Spruce Pine, N.C., Sand for the glass industry is 

 recovered from the kaolin deposit in Orange County, 

 Calif. Bauxite is a minor byproduct of some of the 

 kaolin deposits in the Coastal Plain of Georgia and 

 Arkansas. 



BALL CLAY 



The term "ball clay" originates from an early 

 English mining practice of rolling the highly plastic 

 clay into balls vi^eighing 30-50 pounds. The impuri- 

 ties found in ball clay are illite, montmorillonite, 

 and carbonaceous matter. Quartz, as particles of 

 silt and sand size, and iron oxide minerals are vir- 

 tually absent from the best grade ball clays. The 

 color of most ball clay is nearly white, but some 

 colors range from pink to brown and through shades 

 of gray to black. The color after firing is almost 

 white. Ball clays require between 40 and 65 percent 

 water of plasticity to become workable; plasticity, 

 toughness, high dry-green strength, and adhesion 

 are the outstanding characteristics of ball clay. 

 When fired, ball clay becomes dense and vitreous, 

 and its deformation point is between 1670° and 

 1765°C. Whiteware, floor and wall tile, and refrac- 

 tories account for most uses of ball clay, and build- 

 ing brick and paint filler account for minor uses. 



Ball clay was first mined in the United States in 

 1860 near Paris, Tenn., but it was used only by the 

 local pottery industry. Steady production of ball 

 clay began in 1894 when Mr. I. Handle shipped clay 

 from western Tennessee to East Liverpool, Ohio. 

 The production of ball clay in 1969 was 682,000 

 short tons valued at $9.7 million. Tennessee, Ken- 

 tucky, and Mississippi are the major producers, but 

 very small quantities are produced in Maryland, 

 Texas, and California. Production of ball clay has 

 been increasing during the past 50 years (fig. 14) ; 

 however, during the depression years of 1921 and 

 1932-34, production was low, and the amount of 

 ball clay produced yearly is lower now than any 

 other clay commodity. The average value per ton 

 has increased from $6.21 in 1933 to $14.25 in 1969. 



Lenses of ball clay are known to occur in the fol- 

 lowing sedimentary units: Wilcox and Claiborne 

 Formations of Eocene age in Kentucky, Ripley 

 Formation of Cretaceous age and Wilcox and Clai- 

 borne Groups of Eocene age in Tennessee, Fearn 

 Springs Sand Member of the Nanafaha Formation 

 and Claiborne Group of Eocene age in Mississippi, 



Wilcox Formation of Eocene age in Texas, and 

 Potomac Group of Cretaceous age in Maryland. All 

 these units are located in the Coastal Plain and 

 Mississippi Embayment, and most of the best grade 

 ball clays are shipped from the Mississippi Embay- 

 ment area. 



Reserves of ball clay containing the lower per- 

 centages of quartz sand and silt are estimated to be 

 about 4 million tons in Kentucky, Tennessee, and 

 Mississippi. Resources of ball clay are estimated to 

 be more than 50 million tons, but this total includes 

 ball clay containing a percentage of sand and silt 

 higher than that in the deposits now being mined. 



FIRE CLAY 



The term "fire clays" originated from their re- 

 fractory property, the ability to be fired at high 

 temperatures without warping. On the basis of their 

 physical appearance, characteristics, and properties, 

 fire clays can be divided into four categories : plastic 

 clay, semifiint clay, flint clay, and nodular flint clay. 

 The associated minerals are mainly quartz, siderite, 

 feldspar, and rarely anatase. The color of fire clay, 

 controlled primarily by the amount of carbonaceous 

 matter, is mainly some shade of gray, but brown 

 and black are common. The relative plasticity and 

 hardness give a good indication of the refractoriness 

 of each type. The flint and nodular clays have no 

 plasticity and are the hardest and most refractory, 

 deforming when fired at temperatures between 

 1,745° and 1,805°C. The plastic clay is the most 

 plastic and the softest, and it deforms when fired at 

 1,620° to 1,670°C. Ssmiflint clay is intermediate in 

 plasticity and hardness, and it deforms when fired 

 at 1,670° to 1,745°C. The fired colors range from 

 red to buff and gray. Fire clays are used in making 

 refactories, structural brick, sewer pipe, pottery, 

 stoneware, floor and wall tile, and cement and as 

 fillers. 



The first production of fire clay in the United 

 States was in New Jersey where fire clay was mined 

 at Woodbridge in 1816 for shipment to Boston, 

 Mass., and the first plant for making refractory 

 products was built in 1825 at Salamander, N.J. 

 Until 1943, fire clay was the leading clay commodity 

 (fig. 14), but since then, it has been second to the 

 clays of the miscellaneous group. The demand for 

 fire clay increased to a peak production of 11.8 

 million short tons in 1957, and since then produc- 

 tion has steadily declined to 7.2 million short tons 

 in 1969. This decline is due to the major change by 

 the steel industry from open-hearth furnaces to 

 basic oxygen furnaces. The production of fire clay 



