Polyvanadic acid interacts with bentonite clay in aqueous colloidal suspension, yielding a green, flocculent material. The slow evaporation of the xerogel suspensions leads to insoluble lamellar solids, exhibiting basal distances of 13.0 Angstrom, and a strong intervalence transfer band around 1150 nm. Scanning electron microscopy images show the existence of interconnected nodules containing a uniform distribution of vanadium ions and aluminum-silicates. Evidence of poly vanadate-bentonite interaction is provided by the FTIR spectra, from the appearance of a strong peak at 835 cm(-1), tentatively ascribed to a V-O-Si vibration. The constitution of the green composite depends on the relative amounts of bentonite and polyvanadic acid employed in the synthesis, following the approximate composition bentonite.y(V2O5).z(H2O), where y = 1.5-4.0, and z = 5-12, and bentonite approximate to Na-x(Al2-xMgx)(OH)(2)Si4O10. The dramatic changes in the solubility and aggregation properties corroborate the spectroscopic evidence of strong interactions between polyvanadic acid and the bentonite particles.