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.

One of the alteration products of a deuteric altered beryl is a high-aluminous chlorite-swelling chlorite regular mixed-layer clay mineral. An attempt was made to calculate the structural formula, and the results of X-ray, differential thermal and electron diffraction analyses are given.

Basal spacing data for neutral amine complexes with montmorillonite and vermiculite are explained on the basis of two layers of fully extended amine molecules inclined at about 65° to (001) with the NH2 groups closely associated with pairs of silicate oxygen atoms. The molecular orientation is shown to be favourable for good intermolecular packing and for possible NH..O bonding, but the results do not constitute proof of such bonding. Packing of the molecules on the silicate surfaces and with respect to each other may explain the formation of double layer complexes. The amine data are correlated with corresponding data for the low-temperature (or below melting point) series of alcohol-montmorillonite complexes and it is suggested that the molecular layers may have some solid-like characteristics.

Seven samples, representative of all zones of the Upper Chalk in the Arundel area of Sussex, were treated with acetic acid and the residues analysed to determine their mechanical and mineralogical compositions. The sand and silt fractions of the residues consist mainly of flint and opaline silica, collophane, limonite, and quartz, and the clay fractions consist of montmorillonite, mica, quartz, and apatite. Authigenic apatite and quartz occur in the clay and silt and authigenic alkali feldspar in the silt. The montmorillonite may also be authigenic.

The industrial applications of Fullers' Earth are discussed including those of the clay in its natural form, calcium montmorillonite, and after modification by acid activation or sodium exchange. Special consideration is given to uses in oil refining, foundry bonding, civil engineering, and agriculture.