The weathering of phlogopite mica through vermiculite to saponite was demonstrated by X‐ray diffraction (XRD), quantitative mineralogical analysis and electronoscopic studies. The sand grain sized flakes showed highly crystalline (high intensities at 10Å with K saturation) minerals with a high degree of interstratification of mica‐vermiculite (12.4Å) and mica‐saponite (27.5Å) as well as discrete mica (10Å), vermiculite (14.9Å), and saponite (19.2Å) phases with Mg saturation and glycerol solvation. The saponite increased from 48% in the coarse clay to 70 to 72% in the fine and medium clay, while vermiculite decreased from 34% in the coarse clay to 12 to 17% in the fine and medium clay fractions. Scanning electron microscopy (SEM) of Li + ‐saturated, electrical double‐layer‐swollen, freeze‐dried macroflakes of phlogopite revealed that saponite layers glided out from interstratified sites within the mica and folded at the mica‐vermiculite grain boundary. Authigenic mica needles were observed at some flake margins. A visual model of the formation of the expansible phyllosilicate clays, vermiculite and saponite, from mica is provided. Significant amounts of 137 Cs + fixation and 90 Sr 2+ trapping is to be expected in such systems.
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Jackson et al. (1974) studied this question.