Nature of the Illitic Phase Associated with Randomly Interstratified Smectite/Illite in Soils*

D. A. Laird1 and E. A. Nater2
1 USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, Iowa 50011
2 Department of Soil Science, University of Minnesota, 1991 Upper Buford Circle, St. Paul, Minnesota 55108
* Joint contribution of the USDA-ARS and the Minnesota Agricultural Experimental Station. Paper 19,876 of the Scientific Journal Series.

Abstract: A dispersion-centrifugation-decantation procedure was used to isolate various particle size fractions from a sample of clay (<2 µm fraction) separated by sedimentation from the Ap horizon of a Webster soil (fine-loamy, mixed, mesic Typic Haplaquoll). The 0.02–0.06 µm size fraction was found to be enriched in an illitic phase associated with randomly interstratified smectite/illite. X-ray powder diffraction, chemical analysis, and high-resolution transmission electron microscopy confirmed that most of the illitic material in the 0.02–0.06 µm size fraction was composed of two-layer elementary illite particles with a layer charge of −0.47 per formula unit. The results demonstrate that this low-charge illitic phase can be physically separated from soil materials and that the low-charge illitic phase has chemical, morphological, and mineralogical properties that are uniquely different from those of smectite and illite.

Key Words: Chemical analysis • Elementary particle • High-resolution transmission electron microscopy • Illite • Interstratified • Smectite • Smectite/illite

Clays and Clay Minerals; June 1993 v. 41; no. 3; p. 280-287; DOI: 10.1346/CCMN.1993.0410302
© 1993, The Clay Minerals Society
Clay Minerals Society (www.clays.org)