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Granitic weathering: a Brazilian study
Author(s) -
MELFI A. J.,
CERRI C. C.,
KRONBERG B. I.,
FYFE W. S.,
McKIN B.
Publication year - 1983
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1983.tb01076.x
Subject(s) - kaolinite , weathering , feldspar , mica , vermiculite , quartz , mineral , mineralogy , clay minerals , geology , leaching (pedology) , geochemistry , muscovite , chemistry , soil science , soil water , paleontology , organic chemistry
Summary Chemical and mineral studies were carried out on weathered materials from six profiles developed on granites located in different areas of Brazil. Quartz and K‐feldspar are the most abundant minerals overall. Kaolinite is the most common secondary mineral and is principally a feldspar weathering product. Mica breakdown is associated with smectite formation in semi‐arid regions. In more humid regions mica weathering products include interlayered mica‐vermiculite, vermiculite and kaolinite. Changes in the concentrations of Si, Al and K reflect the weathering behaviour of quartz, kaolinite, K‐feldspar respectively, although K mobilities sometimes appear to be governed by processes related to the formation of secondary minerals. Ca and Mg are the first elements to exhibit depletion and their removal rates are very fast relative to K. P is also among the most mobile elements. Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba and Pb concentrations were measured. The first row transition metals are the most depleted. Rb and Sr are retained relative to Na, Mg, and Ca, and Ba accumulates as weathering proceeds. Y, Zr, Nb and Pb concentrations show little variation. The conclusion is that the factors controlling deep leaching are complex and the common notion that weathering rates are higher at lower latitudes should be reassessed.