Genesis of Maryland Soils Formed from Serpentinite

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Abstract
Four pedons developed over serpentinite were characterized. Eluvial and illuvial processes have caused formation of weak‐to‐moderately‐expressed argillic horizons. Magnesium‐rich parent materials are responsible for the dominance of Mg on the exchange complex, except in surface horizons where H+ prevailed. Also due to the Mgrich parent materials, extractable Ca/Mg ratios decreased with depth ranging from 0.8 to 2.45 at the surface to 0.03 to 0.17 above the bedrock. The pH values increased with depth from 4.9 to 5.6 at the surface to 6.6 to 6.8 above the bedrock. Total nickel and chromium concentrations were between 180 and 18,900 ppm and 400 to 5,850 ppm, respectively.Weathering of serpentine minerals tends toward the formation of smectite, which, with vermiculite, dominates the fine (clay) fractions. These are often interstratified with hydroxyinterlayered minerals. Serpentine minerals, while absent from the <0.2‐µm fraction, occurred with chlorite and vermiculite in the 2‐ to 5‐ and 0.2‐ to 2‐µm fractions. The presence of the silicon‐rich minerals, mica, feldspars, and quartz in the upper portions of the pedons indicates that some eolian materials have been added to the serpentinite residuum. This is substantiated by elemental analyses of the silt fractions.