Interstratified Montmorillonite-Mica Clays from Subsoils of the Prairie Provinces, Western Canada

Abstract

Abstract Samples of glacial till and lacustrine soil clays selected over a distance of 900 miles across the Canadian Prairie Provinces were examined in detail by X-ray, chemical, thermal, infrared-absorption and electron-microscope methods. All of the experimental evidence indicated a marked similarity among the samples. The dominant component was an 18 Å phase when glycerol-solvated, which was identified as a randomly interstratified montmorillonite-mica. This was associated with minor amounts of a 10 Å phase (randomly interstratified mica-montmorillonite), kaolinite and quartz. Fourier transforms of the basal series of reflections gave contents of expanded material (montmorillonite) near 55 per cent, whereas calculation of the chemical formula gave near 80 per cent montmorillonite in the interstratified component. The Fourier transforms confirmed the random nature of the interstratification but also showed a tendency to zonal segregation of the mica and montmorillonite layers. On the basis of the chemical formula, the Greene-Kelly test and the infrared spectra, the swelling layer composition was intermediate between that of beidellite and that of Wyoming bentonite. Although there were no large differences between the samples, the small differences suggested two trends differentiating the till samples and the lacustrine samples: (1) The proportion of the expanded component of the interstratified mineral tended to be less in the lacustrine than in the till samples. (2) The composition of the expanding layers in the lacustrine samples tended to be nearer to the Wyoming bentonite composition than were the till samples. These trends are likely related to K fixation during or after deposition of the lacustrine materials, whereby the expanding layers with a beidellitic composition would be pre-empted leaving layers more similar to Wyoming bentonite.