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.

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.

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.

A new method for estimating the sulphide content of samples of impermeable rocks is described. It is based on the oxidation of reducing substances by nitric acid and titration with permanganate of the nitrous oxides absorbed by potash.

Delta alumina is a transition form obtained during the conversion of boehmite to corundum. Alternative methods have been found for preparing this alumina in a well crystallised condition, enabling detailed X-ray powder data to be compiled. The X-ray data are accounted for by a large tetragonal structure cell of which the axial ratio is 1·47, or 3/2 times the axial ratio of the spinel-like pseudo-cell of Saalfeld. The lattice parameters are a 0=7·96 Å and c 0=11·70 Å. This large cell provides an integral number of vacancies, contrasting with the 2⅔ vacancies of the pseudo-cell, and allows the atomic arrangement to be ordered.

Dehydration curves have been obtained for vermiculite saturated with Mg2+, Ca2+, Sr2+, Ba2+ and Na2+. Three of the hydration phases of Mg-vermiculite give energies of hydration of −3·8±0·1, −5·5±0·1, and −18±3 K cal per mole of water. The heat of hydration of vermiculite has been found to vary with the saturating cation, and to decrease with decreasing energy of hydration of the cation. Values for the heats of hydration of vermiculite saturated with Mg2+, Ca2+, Sr2+, Ba2+ and Na+ are reported.

Complexes of vermiculite with neutral and ionic amines have been prepared and investigated by X-ray diffraction techniques. The results enable certain conclusions to be drawn regarding the structure of such complexes.

X-ray powder diffraction data were used to determine the mineralogical composition of the fine suspended material present in nine English rivers. The mineralogy of these solids is discussed in relation to the geological formations through which the rivers flow.

A simple method is described for determining the approximate positions of Li+, Mg2+ and Ca2+ in three montmorillonite samples saturated with these cations and subsequently dehydroxylated. The method depends only upon changes in the relative intensity of the three lowest order basal reflections, and its applicability to other problems is illustrated.

The chemical method for preparing pseudo-chlorite from montmorillonite suffers from the disadvantage that the magnesium hydroxide is soluble in the ammonium chloride formed. The electrolytic method described overcomes this difficulty and, in addition, gives preparations with up to five brucite layers between the montmorillonite sheets. Ions other than magnesium may also be used. A simple technique for overcoming difficulties associated with preferred orientation in the Brindley powder X-ray camera is described.

Montmorillonite is found to be a predominant clay mineral in the < 2µ fraction of the A2 horizon of podzol profiles in Fennoscandia, even when these are only 300 years old. In fractions between 2µ and 20µ vermiculite and hydrobiotite predominate, but are rarely detected in the fraction coarser than 20µ. Vermiculite and hydrobiotite are also found in the finer fractions of the B horizon, but are only rarely detected in the C horizon where their presence is apparently due to contamination with interglacial or older products of weathering. The presence of kaolinite in some profiles is explicable in the same way.

Fresh samples of some Scottish basic igneous rocks contain two-component interstratified minerals consisting mainly of layers of chlorite, swelling chlorite and saponite in different combinations. The differential thermal curves are characteristic of swelling chlorite.

Some minerals which have been referred to as corrensite are considered together with some related minerals. It is suggested that the name corrensite be retained for the original material so described—namely, a I:1 regular interstratification of chlorite and swelling chlorite. The possible constitution of swelling chlorite, its difference from vermiculite, and its relationship to labile chlorites produced synthetically are all discussed.

Analyses of shales, mudstones and associated strata from the British Coal Measures reflect the general similarity of the clay mineralogy of the rocks studied. Variations in the Na+:K+ ratio appear to be due to variations in the Na+:K+ ratio in illite. It is suggested that degraded illite supplied to the site of sedimentation had a higher Na+:K+ ratio than the illite now present in the shales and that post-depositional changes have caused a fall in this ratio. Under conditions of rapid sedimentation such changes tend to be inhibited by rapid burial. In the seat earths, produced by very slow sedimentation, post-depositional changes continued to an advanced stage and resulted in low Na+:K+ ratio in the final sedimentary rock.

A previous classification scheme for clay minerals is revised and extended; the underlying principles are analyzed in detail.