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A Mineralogical Characterization of Some Loess-Derived Soils in Illinois¹

ABSTRACT

Six soil profiles representing successive stages of development in Peorian loess were studied by X-ray diffraction to determine any changes in mineralogical composition of the silt fraction in relation to their maturity. The quartz, albite, and microcline contents were determined using NaF as an internal standard. The dolomite content was determined with the carbon-induction furnace. The quartz content of the fine silt fraction increased progressively in the A horizons, did not change significantly in the B horizons, and increased slightly in the C horizons with distance from the loess source or bluff. Concomitant with the increase in quartz in the A horizons the feldspar content decreased, indicating the greater susceptibility of the latter to weathering. The slight increase in quartz content in the C horizons was due to the presence of dolomite in the younger soils and the absence of dolomite in the more mature soils. Quartz/feldspar ratios, an index of the weathering of the minerals, increased significantly for the fine silt fraction with increasing distance from the loess source. Albite weathered at a faster rate than microcline in the fine silt fractions. No significant change in the quartz and feldspar content of the coarse silt fraction was observed.

¹ Contribution from the Department of Agronomy, Illinois Agr. Exp. Sta., Urbana. Published with the approval of the Director of the Illinois Agr. Exp. Sta.

² Graduate Assistant and Associate Professor of Soil Physics, respectively.

Received for publication May 27, 1958. Accepted for publication December 1, 1958.