Potassium fixation in smectite

Eberl, D. D., Srodon, J., and Northrop, H. R. (1986). Potassium fixation in smectite by wetting and drying. In "Geochemical Processes at Mineral Surfaces," pp. 296-325. American Chemical Society, Washington, DC, ACS Symposium Series 323. 

One might attempt to state only the condition of the true mica portions of these particles and to place the nonmica portions with vermiculite or smectite, but if this is done, very important features involving ion selectivity and fixation of the particles are ignored. Soil smectites often contain potassium in sufficient amount to suggest small mica zones not detected by X-ray diffraction (Schwertmann [1962a]). 

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