QUANTITAT IVE DETERMINAT ION OF THE INTERLAMELLAR VOLUME IN AN INTERSTRATIF IED MICA-SMECTITE SOIL CLAY

ABSTRACT: Two well-characterized soils containing substantial mounts of interstratified mica-smectite have been examined by a combination oftechniques in an attempt to correlate the characteristics of the interlamellar surfaces with other properties. The techniques u ed included XRD and chemical analyses, determination f surface area by nitrogen sorption and by desorp-tion of water and ethylene glycol monoethyl ether vapour, and determination f cation exchange capacity. Reasonable agreement was found between the results obtained for the proportion of expanding or smectite-like surfaces, although estimates by XRD, especially when coarser material (> 2/~m) was included, were generally lower than those obtained by the other methods. The mean density of charge on the surfaces of the soil clays appeared to be similar to that of smectite. The decrease inporosity observed for both soils dried by the critical point method was largely accounted for by the decrease in volume associated with the loss of interlamellar water from the smectite-like interlamellar surfaces included within the clay fraction. Many soil clays which show substantial swelling and shrinkage in response to changes in moisture content contain smectites in the clay fraction. Commonly the smectite is interstratified or mixed with other 2:1 lattice clays. It is sometimes suggested that th