Abstract: Alteration products of volcanic materials from various localities in Wyoming, U.S.A., Italy, Yugoslavia and Mozambique are mainly smectites and cristobalites with small amounts of kaolinite.
Smectite and cristobalite form separate and intergrown aggregates of microcristallinity. X-ray diffraction studies show that the silica is α-cristobalite with a noticeable stacking disorder. Small aggregates of optically pure α-cristobalite, which were separated by an appropriate mixture of bromo-form and carbon tetrachloride, are shown to contain a noticeable amount of smectite on Debye-Scherrer diffraction photographs for the samples from Italy and Wyoming, U.S.A.
Transmission electron micrographs and selected area electron diffraction photographs show, in addition to smectite and α-cristobalite aggregates, the presence of idiomorph single crystals of kaolinite.