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Micromorphology and Mineralogy of Illuviated Clay in a Davidson Soil

Goenadi, Didiek H., Tan, Kim H.
Soil Science Society of America journal 1989 v.53 no.3 pp. 967-971
A horizons, Paleudults, X-ray diffraction, argillic horizons, clay, fabrics, feldspar, illuviation, iron oxides, kaolinite, leaching, microstructure, piedmont, saprolite, soil fabric, weathering
Clay illuviation was studied in a highly weathered soil of the Southern Piedmont by macro- and micromorphological techniques. Five pedons of a Davidson soil (Rhodic Paleudult) were sampled from four counties for preparation of thin sections and analysis of soil matrix, illuviated clay and argillans. The related distribution pattern of the soil fabric in the epipedon was different than that in the argillic horizon or saprolite. A single-spaced porphyric fabric was found in the A horizon, which had no illuvial clays. The argillic horizon exhibited an open-spaced porphyric fabric with illuvial clay ranging in concentrations from 2.4 to 5.6%. A double-spaced porphyric fabric was noticed in the saprolite, which contained 1.4% illuvial clay. X-ray diffraction analysis of clays in the soil matrix vs. argillans showed strong evidence for kaolinite as the major mineral eluviated from the upper horizon. The data also suggested that, in the argillic horizon, kaolinite was formed in situ through alteration of K-feldspar minerals. The relatively high contents of kaolinite and iron-oxide minerals, together with the presence of prominent argillans in the argillic horizons, indicated that the soil has undergone an intensive weathering and leaching process.