Among early observers of the origin and occurrence of clay minerals were those geologists who described the hyarothermal alteration of felspar in granite to kaolinite and of some basic igneous rocks to fuller's earth. There were speculations into the origin of bauxite and laterite and of the effect of weathering on various rocks and minerals in different climates. Little progressr however, was made until clay minerals could be identified by X-ray diffraction and other methods.

Modern studies (Grim 1953) of the formation of clay minerals begin with Noll's hydrothermal synthesis of montmorillonite (1930), pyrophyllite, kaolinite, and mica (1936); since then, most of the clay minerals have been synthesised from their oxides, though attapulgite and hydrated halloysite have not yet been made in the laboratory. Even to-day not enough experimental observations have been made to allow really convincing phase-rule diagrams of these hydrated systems to be made.

For the routine analysis of soil clay fractions in this laboratory, a camera of the type described by Brindley and Robinson (1946) and by Robinson (1946) has proved very satisfactory. In this camera the clay aggregate is mounted on a flat glass slip which may be set at any desired angle to the incident beam.

Oriented aggregates may be prepared by the evaporation or centrifuging of dilute clay suspensions (Bradley et al 1937, Nagelschmidt 1941, Brown 1953) or by pressure (Mitchell 1953), the dry aggregate in each case being cut up and mounted as required. When using a Brindley-Robinson camera, however, it has been found most satisfactory to deposit the aggregate directly onto the specimen slip by centrifuging.

A suitable centrifuge tube, consisting of a body and base-plug turned out of “Perspex” is shown in the figure. The glass specimen slip fits into a depression of its own shape and size machined in the top of the base.

Data are presented for the effects of wet and dry grinding on dickite from Ouray, Colorado. With increase in dry grinding time the endothermic d.t.a. peak becomes broader and moves towards a lower temperature, while the exothermic reaction is greatly sharpened. Weight loss data, demonstrate greater water loss from ground material and over a longer temperature range. X-ray powder photographs show that after a relatively short period of grinding little further destruction of the lattice occurs, and this lattice destruction apparently proceeds only to a certain stage, for high order spacings of hkl are very persistent.

A colloquium was held on the 8th-9th July, 1955, in the Zaidin experimental station. The object was to give an account of the work which has been carried on recently in the Granada Section of the Institute, and in the Section of Inorganic Chemistry of the University of Granada (Prof. E. Gutiérrez Rios), on clay minerals, and other substances related to clay minerals.

There follows a list of the themes treated, together with brief mentions of the nature of the work in each case.