NATURE OF THE ILLITIC PHASE ASSOCIATED WITH RANDOMLY INTERSTRATIFIED SMECTITE ILLITE IN SOILS

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