Quantitative Evaluation of Feldspar Weathering in Two Boralfs (Gray Luvisols) from Saskatchewan
1986
Mermut, A. R. | Ghebre-Egziabhier, K. | St. Arnaud, R. J.
Fine (0.10-0.25 mm) and medium (0.25-0.50 mm) sand size fractions of two Boralfs (Gray Luvisols) under Boreal forest were used in this study to characterize the nature of feldspars and the extent of their weathering in glacial till soils in northern Saskatchewan. Feldspars were separated into four different specific gravity fractions by heavy liquids. This facilitated subsequent x-ray diffraction (XRD) and chemical analyses used for more accurate quantitative determination of feldspars. Distinctive etch pits were observed by scanning electron microscopy. Infilling of voids in the grains by mostly Fe oxides and some clay minerals was observed under the petrographic microscope. While there is evident recent weathering of feldspars within the solum horizons, there is also evidence of ancient weathering as observed in minerals within the parent materials. The studies verified the presence of microcline, orthoclase, and several solid solution series of plagioclase (mostly oligoclase with inclusions of labradorite-anorthite series). Sodic plagioclases (An ₁₀₋₃₀) were dominant in both profiles, followed by K-feldspars in Profile 1 and calcic plagioclases (An₅₀₋₁₀₀) in Profile 3; this confirmed some differences in mineral composition of the two soil parent materials. Stability of feldspars was calculated using a newly developed pedogenic index. As compared to the E horizons, the lower weathering rates in the Bt horizons were attributed to the illuvial clay, which may have played the role of a protective barrier around the feldspar.
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