Characterization of Aluminum Interlayers in Soil Clays
1965
Frink, C. R.
The amounts of Al, Fe, Mg, K, and Si extracted by sodium citrate from 10 soil clays containing various amounts of chloritized vermiculite are related to changes in cation-exchange capacity (CEC), intensity of the 14A spacing and sample weight loss. Those soils containing abundant interlayers underwent the largest changes in CEC, contained the most citrate-soluble Al and lost the most weight. Although most of the change in CEC and intensity of the 14A spacing occurred in the first 2 hours, Al was steadily extracted from sources of similar solubility for at least 6 hours. Even though the increase in CEC was well correlated with the total Al extracted, it appears that Al interlayers exist as “atolls,” and that not all citrate-soluble Al is contained in interlayer positions. No evidence for the presence of Fe interlayers was found; rather, Fe and Mg appear to exist as contaminants in citrate-soluble Al compounds. A weathering sequence of illite-vermiculite-chloritized vermiculite-gibbsite is proposed for these acid soils. Thus, abundant Al interlayers and low CEC are among the most prominent features of highly weathered acid soils.
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