The exchange capacities, surface areas (both external and total), and heats of immersion in water were measured on a selection of clay minerals and a fine-grained muscovite. The charge density (expressed as 103 X m-eq/m2) of muscovite was 3·6. This was, as expected, much higher than those of clay minerals which tended to group together, the average values being: kaolinites, 2·0; hydrous micas, 1·7; halloysites and montmorillonites, 1.4. The heats of immersion (expressed as J/m2) were, in contrast, more widely spread: muscovite, 0·63; halloysites and kaolinites, 0·49; hydrous micas, 0·28; montmorillonites, 0·14. The explanation advanced for the differences is that they reflect changes in surface energy and cohesion of the silicate layers.

It has been known for some time that when a gel of montmorillonite is freeze-dried the residual clay retains the volume and shape of the gel, and forms a skeleton of low density and some rigidity. Because there is no apparent change in the gel structure during freeze-drying, the dry residues have been studied in the past in an effort to determine the structure of the gels. However, X-ray diffraction measurements have shown that, as a result of freeze-drying, the distance between the elementary layers of Na-montmorillonite drops from high spacings (>30 Å) to zero. The present investigation demonstrates that the main reduction in interlayer spacing takes place on freezing, with a further small collapse on drying. Na-montmorillonite gels, swollen oriented aggregates of Na-montmorillonite and Na-nontronite, and swollen single crystals of Li-vermiculite and butylammonium-vermiculite, all behave in the above manner.

The relationships between the shapes of kaolinite and dickite differential thermal curves are described. The slope ratios of dickite are distinctly greater than those of kaolinite of equivalent particle size for the endothermic peak at about 550ºC and the same effect is observed for the exothermic peak at about 980ºC especially in diluted samples. The packing density of dickite does not differ markedly from that of kaolinite and the curve obtained for weight vs. area of the endothermic peak is in agreement with this. The dickite samples, however, give slightly lower areas than those of kaolinite, an effect that is dependent on the shape of the particles. The exothermic peak is shown to be influenced considerably in shape and size by thermal gradients.

A thin vein of a white powdery material situated in massive syenite was examined by various methods and found to consist of an association of a zeolite with calcium montmorillonite, which seems to have been formed by the slow but prolonged action of water on nepheline.

Mineralogical compositions have been calculated from a number of average analyses of shales and clays using the scheme of Imbrie and Poldervaart (1959). The average shale comprises 59 per cent. clay minerals, 20 per cent. quartz and chert, 8 per cent. felspars, 7 per cent. carbonates, 3 per cent. iron oxide minerals, 1 per cent. organic matter and 2 per cent. other minerals. Illite predominates among the clay minerals.

A new method is described for determining in shales the amount of sulphides that dissolve in dilute hydrochloric acid. The samples are treated with hydrochloric acid under vacuum, and the hydrogen sulphide evolved is absorbed in potassium hydroxide and titrated with potassium permanganate. The analytical results are expressed as FeS.