ELECTRON SP IN RESONANCE STUDIES OF MONTMORILLONITES

ation criteria) from the Gurasada bentonite deposits, Romania, were investigatecl by ESR. The spectra showed two features: a g-4.3 signal attributed to isolated Fe 3+ ions and a broad resonance with g ~ 2.0 which was interpreted as arising from exchange interactions between clusters of Fe 3+ ions. Additional experiments suggested that the latter esonance could have a structural component. The line-shape of the two resonances varied between ormal and abnormal montmorillonites, indicating that the distribution of the Fe 3+ ions between i ternal phase (montmorillonite lattice) and external phase (montmorillonite surface) was different for the two varieties. In the Gurasada region of Romania, two montmoril lonite varieties have been reported (Cr~ciun, 1978) which show differences in dehydroxylation behaviour. One variety shows a single dehydroxylation reaction at ~700 ~ and the other shows a double dehydroxyl-ation peak system with peaks at ~550 and 680 ~ Using the terminology of Mackenzie (1970), these would be classed as normal and abnormal, respectively. In spite of the fact that the 001 basal spacings are similar, the two varieties show distinct differences in intensity and width of the 001 reflection after Ca-saturation and glycolation, the norma