Electron microscopy was used to study swollen samples of n-butylammonium vermiculite prepared in dilute aqueous solutions of n-butylammonium chloride. Three electrolyte concentrations were studied, 0.1 M, 0.01 M and 0.001 M. The 0.1 M samples studied were in a taetoid phase, exhibiting crystalline legions of about ten layers separated by large irregular aqueous regions. The dilute samples were studied in their gel phase, exhibiting regular spacings of 85 nm and 55 nm in the 0.001 M and 0.01 M

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... lutions, respectively. These spacings are much larger than those measured previously by neutron scattering, probably due to an additional expansion of the interlayers during the freezing process employed in preparing the replicas. In all examples, the structures were found to be lamellar over regions of several microns.