Properties of Vermiculites and Smectites: Expansion and Collapse*

M. E. Harward, D. D. Carstea and A. H. Sayegh
Soils Department, Oregon State University, Corvallis, Oregon
* Technical paper 2521, Oregon Agricultural Experiment Station. The investigation was supported in part by Public Health Service Research Grant WP-00097 from the Division of Water Supply and Pollution Control. Discussions with G. F. Walker on choice of samples and treatments prior to initiation of the study and with G. W. Brindley during the course of investigations are gratefully acknowledged.
Present addresses, Oregon State University; U.S. Geological Survey, Water Resources Division, Philadelphia, Penna.; and Faculty of Agricultural Sciences, American University of Beirut, Beirut, Lebanon, respectively.

Abstract: Samples of smectites and vermiculites were evaluated to (1) determine the effects of source and amount of charge, (2) determine if a continuum of properties exists, and (3) improve the basis for differentiating criteria for identification.

The montmorillonites expanded to the equivalent two-layer complex upon solvation by condensation of ethylene glycol or glycerol vapor. Beidellite exhibited the one-layer complex with glycerol vapor and the two-layer complex with ethylene glycol. The vermiculite samples did not yield regular two-layer complexes regardless of saturating cation, prior moisture or solvating agent. A number of different complexes of vermiculite were obtained depending on conditions of solvation. These corresponded to spacings of approx 13·6, 14·0, 14·3, 15·0, and 15·3 Å. Two or more of the complexes may be present in the same sample.

Potassium-saturated vermiculites and smectites both exhibited collapsed layers in a dry atmosphere. Hydration of smectites occurred at humidities above 20 per cent and resulted in poorly ordered diffraction maxima of 11–12 Å. The K-saturated vermiculites tended to retain the collapsed lattice and exhibited diffraction maxima of 10–10·6 Å with integral higher orders. Some hydration occurred as evidenced by peak asymmetry or the appearance of a small 14·3 Å line at higher humidities, although the collapsed spacing predominated. The tendency of vermiculite to hydrate decreased as the exchange capacity increased.

Differences in properties can be related to both source and amount of charge. Nevertheless, a continuum in the properties of expansion and collapse between the smectites and vermiculites was not observed. The data indicate two discrete populations. These properties may be used as differentiating criteria for identification.

Clays and Clay Minerals; January 1969 v. 16; no. 6; p. 437-447; DOI: 10.1346/CCMN.1969.0160605
© 1969, The Clay Minerals Society
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