Distribution of Clay Minerals and Ion-Exchange Capacity in Some Sedimentary Materials

Abstract The cation-exchange capacity of the clay fraction was determined in 67 samples of various types of sedimentary materials, and the clay minerals were identified from x-ray diffractometer patterns of oriented aggregates. The probable quantitative clay mineral composition was established for each sample assuming a comparable degree of crystallinity for the clay minerals in the sample. Agreement was poor between the ion-exchange capacities determined and those predicted from the clay mineral composition. The results suggest that the figure obtained for the ion-exchange capacity of a sample of sedimentary material may be misleading as a guide to the types of clay minerals present. The residual soils among the sedimentary materials examined had clay fractions with greater variation in ion-exchange capacity than did unconsolidated sediments generally of alluvial origin.