ILLITE IN THE HOT-ARIDIC SOIL ENVIRONMENT

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Abstract
Illite is shown to be dominating the clay fractions of some aridic soils, while being nearly absent in many others. Water extract compositions from aridic soils suggest solutions in equilibrium with mixed layers of illite/smectite. Illite is considered to be a stable clay mineral in the aridic pedoenvironment. Concentration of illite in the fine clay fractions of some soils and clay transformation sequences in soils developed from magmatic rocks suggest that some illite is of pedogenic origin. Illite accumulations in the upper most horizons of many aridic soils, as well as soluble and exchangeable K+ gradients that decrease downward in the soil profiles, suggest that illite pedogenesis takes place in the uppermost soil horizon. Atmospheric dry fallout (dust) and wet fallout (aerosols) are proposed as the sources of the required potassium for illitization and sequential wetting-drying cycles of the soils are proposed as the mechanism responsible for the process. The distribution of illite in aridic soils can partly be explained by the length of time and intensity (number of deposition-deflation/wetting-drying cycles) at which this process has taken place.