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Sericites in Feldspars as Source of 2:1 Phyllosilicates in Selected Sandy Soils

Dep. of Soil Science, Univ. of Alberta, Edmonton, Alberta, Canada T6G 2E3

*Corresponding author.

ABSTRACT

The high content of 2:1 phyllosilicates in the eluvial horizon of many sandy forested soils in North America is attributed to extraneous deposition. In this study, we evaluated the hypothesis that sericite in feldspars is a local source of 2:1 phyllosilicate by investigation of thin sections and coarse sand fractions from three pedons in an Alfisol-Spodosol association developed on Quaternary sandy deposits in Alberta. In situ investigation of the alteration products of feldspar weathering was conducted by using x-ray microdiffraction techniques, light and electron microscopy, and layer charge density by alkyl ammonium saturation technique. The nature of the minerals in the bulk samples and total elemental composition of the sand fractions were also investigated. Results showed that feldspars occur as orthoclase, microcline, and albite. Some of the feldspar grains were perthitic in nature. The weathering of feldspars is characterized by linear striations (parallel and cross linear) and starts mainly from grain fractures and twin planes. Several types of 2:1 phyllosilicates were identified in the alteration products: (i) a component with a fixed basal spacing around 1.0 nm, (ii) a high-charge component with a charge density of about 0.6 mol_c [(Si, Al)₄O₁₀]^–1, (iii) a low-charge component with charge density of about 0.34 mol_c [(Si, Al)₄O₁₀]^–1, and (iv) an interstratified component comprising of both the low- and high-charge components.

Received for publication December 3, 1992.