Abstract: The electron spin resonance of some structural Fe3+ for montmorillonites having low Fe3+ content, is perturbed by electrostatic interaction between exchange cations and structural charge sites. The position of charge centers of organic and inorganic cations in the interlayer can thus be determined at various levels of solvation. Dielectric media between the silicate layers lower the electrostatic attraction between the silicate and the exchange cations. The silicate charge appears to be partially delocalized on structural oxygen atoms as shown by electron spin resonance and i.r. spectroscopy. There is also evidence that divalent exchange cations on dehydrated montmorillonites cause hydrolysis of water; the protons so produced migrate to structural charge sites.