Experiments carried out in the author's laboratory on the artificial weathering, in an open system, of potash felspar, albite, leucite, tremolite, olivine, sideromelane, muscovite, and clay minerals are reviewed. The results are assessed, and eventually compared on the basis of the amount of SiO2 removed after leaching with 4 1 solvent.

An experimental procedure has been devised for studying the weathering of rocks under conditions approximating to those of the humid tropics. Basalt and trachyandesite gave results which were broadly similar in that a deeply weathered skin was formed on the rock particles in the atmospheric zone while a greyish skin was formed on the particles in the zone of water-table fluctuation. Granite, on the other hand, had a markedly different reaction and the particles in the atmospheric zone had a characteristic ‘pumice stone’ appearance. The new minerals formed during weathering are discussed as well as the geochemical changes occurring and an overall balance sheet for the weathering of these rocks is drawn up. The results obtained in this study are compared with those observed in the field.

It is suggested that the source materials of the English Aptian fuller’s earths were soils of the Anglo-Belgian Land and that montmorillonite is the characteristic clay mineral of marine deposits formed when old land surfaces of low relief are transgressed.

The use of thermal and acid treatments, prior to X-ray diffraction examination, for the identification of kaolinite and chlorite in mixture is discussed. Thermal treatment, although useful in confirming the presence of chlorite, cannot give definite information on the presence of kaolinite, but acid treatment is conclusive in this respect.

The possibility of the identification by X-ray diffraction of montmorillonite and swelling chlorite, in the presence or absence of each other, is discussed. Swelling chlorite or montmorillonite, even in mixture with normal chlorite, but in the absence of mica, can be identified by heating to 500°C with immediate sealing of the tube, or by acid treatment followed by solvation with ethylene glycol. If mica is present, however, only the latter procedure will usually ensure positive identification. The same procedures will differentiate montmorillonite and swelling chlorite in mixture only when normal chlorite is absent.

The <2μ equivalent spherical diameter (e.s.d.) fraction of the Ap horizon of a Brown Earth from Salamanca developed on Cambrian shales under a semi-arid climate with predominantly physical weathering has been studied. From X-ray diffraction results the mineralogical composition of this clay is: illite—70 per cent. kaolinite—10 per cent. and a “dioctahedral clay vermiculite”—20 per cent. The properties of the last mineral are detailed.

A new collimator of 0.3 × 2 mm aperture and a beam trap have been made for the Philips 114.83 mm camera. As a result of this, longer spacings cart be recorded (d=35 Å with Co Kα, with scope for further improvement by slimming the beam trap) the resolution of the camera has been improved, the background scatter is considerably reduced, and the exposure time is reduced by about one-third, in comparison with the standard collimator of 1 mm diameter.

A description is given of modifications that have been made to standard Philips powder cameras to render them suitable for recording high spacings in clay mineral work.

A simple jig is described for the construction of a model of the muscovite structure in which the distorted hexagonal, i.e., ditrigonal, arrangement of the basal oxygens of the tetrahedra is accurately represented. The model is of the packing kind as opposed to the ball-and-spoke kind and demonstrates the advantages of this type of model, which would be more generally used if transparent plastic balls were available commercially.