Significance of recent structure determinations of layer silicates for clay studies

Abstract

In the last 10 years or so much work has been done to determine the crystal structures of layer silicates more precisely than previously and, as a result, ideas about these structures have had to be revised.Around 1930 the classical studies of Bragg and his collaborators, and of Pauling, established the general geometrical features of layer silicate structures. The basic building units were found to be layers of linked tetrahedra articulated, by sharing oxygens, with layers of octahedra. In the 1 : 1, kaolinite type materials, with layer thicknesses about 7 Å, the composite layer unit was made up of one tetrahedral layer and one octahedral layer; in the mica and chlorite minerals the silicate layer was formed by joining two tetrahedral layers, one on either side, to an octahedral layer.