Influence of Chemical Weathering on Basal Spacings of Clay Minerals

Illite, vermiculite, montmorillonite, kaolinite, and a Brookston soil clay were weathered by H‐, HO‐, and H‐resin; sodium tetraphenyl‐boron + resin; and boiling 1 N nitric acid + resin treatments. X‐ray diffractograms of the treated clays suggest the following effects on the mineral structures. Resin caused relatively minor changes compared to unweathered specimens. NaBPh 4 removed interlayer K from 10A and 10–14A interstratified components of illite, vermiculite, and Brookston soil clay resulting in partial expansion of 10–14A components as evidenced by diffractograms of glycolated samples. HNO 3 dissolved less stable components of the illite specimen and/or favored preferred orientation of aggregates as indicated by marked increases in the intensity of mica basal reflections. Estimations of K content of mica from 10:5A peak‐intensity and area ratios indicated that mica remnants in acid‐treated illite were lower in K than those in unweathered or NaBPh 4 ‐treated illite. Treatment with HNO 3 severely altered the expansibility of vermiculite, transforming a part of the specimen into an expanding lattice structure and dissolving much of the remainder. The 10A and 14A components of Brookston soil clay were less altered by HNO 3 treatment; however, the 17–18A peak in the glycolated sample was sharper, and thermally stable interlayer components were less evident after acid treatment. HNO 3 ‐ and NaBPh 4 ‐treated kaolinite and montmorillonite basal spacings remained essentially the same as untreated samples. These data are evaluated in terms of mechanisms of K‐release from the weathered clays and subsequent K‐content found in soybean plants ( Glycine max L.) grown in the clay residues.