Feldspar weathering profiles

Rates of Feldspar Weathering in Natural Weathering Profiles from Geochemical Mass Balance of Small Watersheds... 

An extensive chemical and microscopic study of mica separated from 21 Piedmont soils from the Piedmont of southeastern United States was made by Denison et al. [1929]. The fraction analyzed was greater in size than that passed through a 200-mesh sieve. Weathering was evident in even these sand-size particles. In all soil profiles, biotite seemed to be altered to the same extent, the K2O content usually approximated 4%. On the other hand, muscovite, as described by the authors, had a wide variance in K2O content. This muscovite in some profiles contained less than 1 % K2O, whereas in other profiles, the mineral contained as much as 9% K2O. The authors proposed that there were two kinds of muscovite present—some secondary, having formed from the products of potassium-feldspar weathering, and some primary, which muscovite inherited from the parent material. The identification of material with 1 % K2O as muscovite would be questioned today. The use of X-ray diffraction for soil clay identification occurred after this microscopic work was done. It would have been useful to examine the < 200-mesh particles to supplement the work done with the microscope on particles of a size greater than 200 mesh. 

In the simulation, CO2 in the soil gas reacts with the feldspars, leading to the alkali leaching and separation of silica from alumina observed to result from soil weathering. Near the top of the profile, the reaction produces gibbsite and adds Na+, K+, and Si02(aq) to the migrating pore fluid, according to the reactions,... 

Vance GF, Boyd SA, Mokma DL (1985) Extraction of phenolic compounds from a Spodosol profile an evaluation of three extractants. Soil Sci 140 412-420 Vance GF, Mokma DL, Boyd SA (1986) Phenolic compounds in soils of hydrosequences and developmental sequences of Spodosols. Soil Sci Soc Am J 50 992-996 Velbel MA (1989) Effect of chemical affinity on feldspar hydrolysis rates in two natural weathering systems. Chem Geol 78 245-253 Weber JH (1988) Binding and transport of metals by humic materials. In Frimmel FH, Christman RF (eds) Humic substances and their role in the environment. Wiley, New York, pp 165-178... 

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