Mineralogical Characteristics and Transformations of a Vertical Rock‐Saprolite‐Soil Sequence in the North Carolina Piedmont: I. Profile Morphology, Chemical Composition, and Mineralogy

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Abstract
A lithologically continuous vertical rock‐saprolite‐soil sequence was studied in order to determine its mineralogical characteristics and transformations. The soil was a Typic Hapludult from the North Carolina Piedmont formed on granitic gneiss. The profile was sampled in 19 horizons, from the surface to slightly altered rock, on the basis of morphology and depth. Though weathering intensity was generally antipathetic with depth, this was not always the case, especially in the deep saprolite where two horizontal weathering fronts moved in opposite directions from a single fracture plane. The soil material differed morphologically from the saprolite by having soil structure and clay skins.Elemental analysis of the samples revealed a release of Ca and Na from the altering rock, and a subsequent decrease in abrasion pH, presumably due to rapid plagioclase alteration. Aluminum seemed to precipitate initially as an Al‐rich clay mineral in the altering rock. However, this clay was rapidly resilicated coincident with a decrease in abrasion pH. The most rapid changes occurred in the deepest saprolite horizons.

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