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Weathering and Mineralogical Classification of Selected Soils in the Blue Ridge Mountains of South Carolina

Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40506

B. R. Smith^*

Dep. of Agronomy and Soils, Clemson Univ., Clemson, SC 29634

*Corresponding author.

ABSTRACT

Four pedons in the Blue Ridge Mountains of South Carolina were studied to determine the mineralogy and weathering in soils in the southern Appalachians. These soils formed in weathered gniess or schist and receive as much as 2160 mm of annual precipitation. Gibbsite increased with increasing slope, elevation, and rainfall, and ranged from 60 to 670 g kg^–1 of the clay fraction (<2.0 µm) and was as high as 140 g kg^–1 of the whole soil (<2.0 mm). Gibbsite is thought to form from weathering of feldspars. Kaolinite ranged from 0 to 470 g kg^–1 in clay fractions and was as high as 380 g kg^–1 of the whole soil. Kaolinite appears to be the product of biotite kaolinization. Hydroxy-Al interlayered vermiculite (HIV) was the dominant clay mineral in surface horizons, with randomly interstratified mica-vermiculite and mica increasing with depth. All four soils met the requirements of the oxidic mineralogy class. Release of Fe from kaolinization of biotite, abundance of gibbsite, and fine-loamy particle-size class of these soils cause them to have quite high oxidic ratios. However, the high weatherable mineral content of these soils is not consistent with the oxidic mineralogy concept that is supposed to represent soils in an advanced weathering stage. If the oxidic class is to separate out intensely weathered soils, then some amendments must be made to exclude less-weathered soils similar to the ones of this study. A maximum of 10% weatherable minerals is proposed as an additional criterion for the oxidic class.

Technical Contribution no. 2877 of the South Carolina Agric. Exp. Stn.

Received for publication September 28, 1988.