Incidence of bloating among approximately 600 clay samples from East Texas, ranging in age from Gulfian (Late Cretaceous) to Recent, correlates principally with clay mineralogy and pH--together an indication of bulk composition--and to a lesser extent with texture, loss on ignition, and content of nonelay refractory minerals. Clay-mineral and pH data permit prediction of bloating with an accuracy of about 80 percent, Montmorillonitic and illitic clays are the best bloaters; bloating occurs in

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... re than 80 percent of clays consisting of less than 30 percent kaolinite, more than 10 percent illite, and between Z0 and 90 percent montmorillonite. Only 10 percent of the highalumina clays (more than 50 percent kaolinite) bloat; these generally are plastic and carbonaceous. Value of pH is an index of the amount of certain flux and gas-forming materials in clays; accordingly, bloating incidence generally increases with increase in pH, Incidence of bloating also increases slightly with decrease in grain size, increase in plasticity, increase in loss on ignition, and decrease in content of nonclay refractory minerals.