Surfaces of weathered minerals associated with soil drainage: A quantitative microscopic evaluation

The use of scanning electron microscopy (SEM) has allowed the viewing of the surfaces of silt and sand sized soil minerals. These surfaces are a record of the weathering history of the grain in a particular pedochemical environment. The objective of this dissertation was to develop SEM techniques for the qualitative evaluation of weathered mineral surfaces, and to apply the techniques in a study of mineral weathering.The optimum method for cleaning grain surfaces, prior to SEM analysis, without inducing artificial weathering artifacts was determined to be gentle overnight shaking in 2% sodium bicarbonate at pH 9.5.Digital image analysis (DIA) was used to evaluate size and shape distributions of etch pits on the surfaces of weathered orthoclase and pyribole grains. An interpretative tracing of the image of etch pits and grain perimeter from projected SEM micrographs was analyzed for size-frequency distributions of etch pits, and etch-pit shape analysis.The quantitative evaluation of etch-pit size and shape distributions on grain surfaces of very fine sand sized orthoclase and pyriboles from a catena of loessal soils revealed that the poorly drained soil had significantly smaller and more numerous etch pits for both minerals. From this it was concluded that mineral weathering increases the number of small pits rather than enlarging existing pits. In horizons of all soils etch-pit size frequency distributions were skewed toward the smallest sizes. Etch-pit shape varied significantly with soil drainage, potentially an indication of differing mechanisms as a function of soil drainage. Etch-pit shape was randomly distributed among size classes. Etch-pit density did not prove to be a useful weathering index for differentiating soils, but for orthoclase did show a depth trend consistent with more traditional weathering indices.U of I OnlyETDs are only available to UIUC Users without author permissio