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Mineralogical Analyses of Soil Clays from Colorado Surface Soils¹

ABSTRACT

Minerals in the fine silt and clay were determined for six cultivated soils in Colorado. The clay fraction was segregated into coarse, medium, and fine particle size groups. By means of combined data from total potash, exchange capacity, water and hydroxyl content, surface measurements, and X-ray diffraction analyses, the relative amounts of minerals in each size fraction were estimated.

The sum of quartz and feldspar ranged from 55 to 70% in the fine silt and from 30 to 55% in the coarse clay. Small amounts of chlorite identified in the fine silt and coarse clay fractions were generally interlayered with 2:1 layer silicates. There was 20 to 36% illite and 4 to 11% kaolinite in the 2µ clay fraction. The total expanding mineral (montmorillonite plus vermiculite) content of the 2µ clay varied from 36 to 57%. The expanding minerals in the soil clays were more variable in properties than standard reference clay minerals. Interstratification of 2:1 layer lattice silicates was observed in all fine silt and clay samples.

Contribution from University of Wisconsin, Madison. The work was supported in part by the University of Wisconsin Research Committee through a grant of funds from the Wisconsin Alumni Research Foundation for support of the first author as a Project Associate for 1 year. A sabbatical leave for the first author from Colorado State University, for the year 1954–55 is gratefully acknowledged. Presented before Div. II, Soil Science Society of America, Nov. 14, 1956, at Cincinnati, Ohio. Submitted for publication Dec. 27, 1956.

² Agronomist, Colorado State University, and Professor of Soils, University of Wisconsin, respectively.

Accepted for publication January 29, 1957.