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

The changes in X-ray diffraction patterns of layer silicates which result from dry heat-treatments below 550°C have been studied and the results are tabulated in order of increasing temperature at which these changes are observed; the structural implications are briefly considered. In order to evaluate the effects of composition, particle size and disorder, synthetic clay minerals have been used in addition to natural clays. This summary of X-ray data may be of value in the identification of clay minerals in mixtures.

A single measurement of the adsorption of atmospheric air on a dried, finely-divided solid at − 183°C carried out in a simple apparatus which does not require a high vacuum system, can be related empirically to the specific surface as determined by the Brunauer, Emmett and Teller procedure, with, generally, less than 10 per cent. error. The method is rapid and simple, and therefore suitable for routine use.

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.

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.

X-ray powder diffraction studies have been made of the structure changes which occur on dehydrating the minerals diaspore and goethite, and also the synthetically-prepared “δ-Fe2O3.” For diaspore and goethite the changes are interpreted in terms of superstructures referred to a hexagonal, anion lattice sub-unit which is common to both the α-type oxyhydroxides and the anhydrous corundum or hematite structures. The ferromagnetic δ oxide, obtained by rapid oxidation of ferrous hydroxide, is shown to be a true oxyhydroxide of the form FeOOH. It transforms into goethite on heating at about 150°C but the change is incomplete due to a tendency to lose water directly to the atmosphere. An approximate structure analysis has been made, using the X-ray powder data for two relatively well-crystallized δ oxide preparations. It is concluded that the ferric ions occupy the interstices of the anion lattice in such a way that approximately 80 per cent. of the iron is randomly distributed in octahedral sites, while the remainder is similarly placed in tetrahedral sites. This cation distribution enables both the transformation to goethite and the magnetic properties of the oxide to be satisfactorily explained.

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.

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.

Seven brickmaking clays from various geological horizons have been studied by differential thermal and X-ray methods. The minerals detected included kaolinite, illite, montmorillonite, chlorite, swelling chlorite, calcite and quartz, and rough estimates were made of the quantities present. For the same clays, deformation-under-load was measured at four different heating rates, and strength and water absorption were determined on fired blocks. No correlation between the firing properties and mineralogical constitution is observable.

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.

Examination of the cation-exchange capacity of a hydrated halloysite from Djebel Debar has disclosed no evidence for the proposed existence of exchangeable interlayer ions. A series of labile halloysite-salt complexes has been prepared. The requirements for effective intercalation of the salt are a high salt concentration in the external solution phase and a cation of low hydration energy.

The transformations in the iron oxide-hydroxide system have been interpreted in a rational crystallochemical manner, some being characterized as topotactic and some as non-topotactic. Crystallographic measurements have been made on the more reactive or metastable phases, particularly on the “green rusts.” The oxyhydroxides β-FeOOH and δ-FeOOH have been examined more fully, but data on all the phases have been checked. New data on transformations, such as FeCO3 → FeO and Fe(OH)2 → FeO are reported.

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 question is raised as to what extent a study of the clay mineralogy enables the detailed ceramic behaviour of a clay to be predicted. It is indicated that the behaviour of a clay in an industrial process is often controlled by other factors, such as particle size distribution of the clay minerals and firing conditions which must, therefore, also be taken into consideration.

The apparatus described enables investigations to be carried out in any desired gas or vapour at pressures not far removed from atmospheric. Two different specimen-holder blocks have been developed: a nickel one for use with inert gases (e.g., nitrogen) and high sensitivity of recording, and a ceramic one for use with active gases and vapours (e.g., oxygen or water vapour) and rather lower sensitivities. Evacuation of the system to pressures of less than 0·05 mm Hg is also possible. The temperature control system consists of a commercial anticipatory temperature controller and a motorized autotransformer; the differential thermal curve is recorded photographically. Some results are given to illustrate the high sensitivity of the apparatus, its application to highlyorganic soil-clays and to the study of combustion reactions.

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.

It is suggested that the exothermic effect which appears on differential thermal curves for certain samples of NH4-montmorillonite may be due to oxidation of the ammonia evolved. Such an effect is suppressed and replaced by an endothermic effect if an inert atmosphere is used.

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.

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 a0=7·96 Å and c0=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.

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.