Abstract--Lepidocrocite was identified associated with mica particles and in the clay fraction of two well-drained Ontario soils developed on a granite and a granite-gneiss. The occurrence of lepidocrocite is rare outside the tropics and there are no reports on its existence in well-drained soils.

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Morphological changes occurring in naturally weathered micas in seven residual soils from Ontario were studied. Splitting, exfoliafion of the (100) planes, surface coats, filling of spaces with soil material as well as cracking and crumbling of (001) surfaces were the main morphological changes found to be taking place during natural weathering of mica particles. The significance of the observed feature in relation to the general theory of mica weathering is discussed.

Mica particles from six residual soils were separated from different horizons and separated into three weathering classes. Potassium contents in the centers and in the edges of mica particles were determined by using electron probe microanalysis techniques. The results showed that biotites tended to regain K after an initial loss becoming more resistant to weathering. The regained K concentrated at the edges of weathered biotite particles.