PROBLEMS IN IDENTIFICATION OF MONTMORILLONITE AND BEIDELLITE

Lack of X-ray-detectable back migration of Li** plus ions from octahedral sites allows the study of the reduced-charged behavior of Li-saturated and heat-treated clays, even under conditions where the samples must remain in the saturating medium for a considerable period of time. This procedure may be extended to employ the Greene-Kelly test combined with alkylammonium ion exchange to estimate the layer charge located in either the octahedral or tetrahedral sheet of an expanding 2:1 clay mineral having considerable charge on both sheets. Low-charge minerals, however, having tetrahedral charge less than 0. 24/half unit cell cannot be completely characterized by alkylammonium ion exchange. The magnitude of tetrahedral or octahedral charge is more important than the relative proportions of octahedral or tetrahedral charge for the identification of montmorillonite and beidellite by the Greene-Kelly test. Considering the existing techniques for identification, a need still exists for the refinement of criteria or the development of a direct and sensitive technique for distinguishing montmorillonite from beidellite.