DISTRIBUTION OF CLAY MINERALS IN SELECTED OKLAHOMA SOILS

Abstract

We quantified the distribution patterns of clay minerals in the coarse (2.0 to 0.2 micrometer) and fine clay fractions of six Oklahoma “Benchmark soils” that vary in climate and geology. The contents of the different clay minerals are needed of the fine and coarse fractions for these soils to obtain a better understanding of crusting, shrinkswell, and other physical and chemical properties of Oklahoma soils. Alkali-soluble amorphous materials from the deferrated clays were not found in large amounts in any of the soils studied. These small amounts of amorphous clays have Si and Al composition similar to montmorillonite. Micaceous minerals were the major clay minerals in the coarse and fine clay fractions of the underlying weathered shales. Montmorillonite dominated the fine clay fractions of all the soils. It was also the major clay mineral in the coarse clay fractions of the soils obtained from subhumid, semiarid areas of Oklahoma. The kaolinite content was high in soils of eastern Oklahoma, which receives more precipitation. Kaolinite, however, was lower in the coarse clay fractions of the A horizons in these soils. Quartz was found in relatively larger amounts in the coarse clay fractions of the A horizons of the highly developed soils in eastern Oklahoma. Vermiculite and chlorite were not found in appreciable amounts in any of the soils studied. The Dennis and Bernow soils contain large amounts of interlayered clay minerals that appear to be common to many Oklahoma soils.