XRD analysis of the mixture revealed a complex powder pattern in which most of the peaks can be identified as Na-montmorillonite . However, by settling a sample of the finely ground mixture in a water column, it was possible to obtain a partial separation of the new phase. The chemical and XRD data therefore strongly indicate that the new phase is a Na zeolite of ferrierite type which has precipitated on the dehydroxylated clay surface. Although there is no direct evidence of the crystalline state of the clay envelope, other recent studies have shown that the alteration of volcanic glass commonly occurs in two stages. Mg is taken-up in the formation of the clay phase.
Conditions then exist which favour zeolite formation.
The present experimental results support this observation and it is thought that reactions of this type, in marine basins rapidly filled by ash falls and pyroclastic flows, are responsible for the pseudomorphic replacement textures seen in the volcanic glass. De'Gennaro, M., and Colla, C. 1992. Experimental clay formation through the action of hot saline waters on volcanic glass. Murat, M., Amokrane, A., Bastide, J. P., and Montanaro, L. 1992. Synthesis of zeolites from thermally activated kaolinite.