Report on the natural occurrence of a silica-clay nanocomposite

A natural occurrence of a silica/clay nanocomposite material was investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). High-resolution images show that this nanocomposite material consists of 5–20 nm thick slabs of smectite and tridymite/cristobalite layers with coincident normals. In spite of the brittle glass-like appearance of the nanocomposite material its colloidal properties are similar to those of pure smectite but partial loss of expansion capacity was detected upon glycerol solvation. The structural relationship between smectite and silica is interpreted based on the smectite structure model of Edelman and Favejee (1940) which supposes reversed tetrahedra in the SiO4 layer of the TOT structure. This structure model explains the presence of silica impurities in bentonites used as raw material and several geological standard montmorillonites.