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.

A number of different commercial vermiculites have been examined and it has been found that the exfoliable minerals can be divided into three main groups; those which give a 26 Å spacing on an X-ray diffraction pattern, those which give a 14 Å spacing, and those which give various spacings and are partially dehydrated. All are mixed-layer minerals of one type or another, but all have some vermiculite layers in their constitution. The expansibility of these minerals is not linked with their structural types, but there is an indication that the largest expansion is associated with the occurrence of hydrobiotite and the lowest expansion with the occurrence of true vermiculite.

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.

A genetic classification of clay rocks is given in which five main types are recognized. In this classification minerals of the kaolin group formed directly from hydrothermal solutions, along with sulphides, sulphates, and pneumatogenic minerals, are separated from the same minerals formed by the hydrothermal-metasomatic action of gases and vapours on aluminosilicate rocks. Some data on the occurrence of these two types in Azerbaijan are recorded. The origin of the bentonitic clays (“gilabi”) of Azerbaljan is also discussed; the geology of the deposits indicates cycles of volcanic activity and long-range transport of volcanic ash.

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.

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 lithium mica extracted magnetically from china stone is compared chemically and by X-ray methods with known lithium micas. This comparison shows a strong resemblance between the Cornish mica and zinnwaldite from the Zinnwald.

Thermal expansion measurements on unfired ceramic clays have provided a useful rapid method of estimating their quartz contents. Reversible thermal expansion measurements on the fired clay reveal changes in composition with firing, notably the development of cristobalite and of the glassy phase.

A report is given of the decisions reached at a meeting on the classification and nomenclature of clay minerals held under the auspices of Comité International pour l’Etude des Argiles at Brussels in July 1958. Tables of recently-proposed classification systems are included and some comments made on problems requiring agreement.

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.

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.

Only recently has it been possible to perform quantitative mineralogical analysis of clays and to establish the crystallochemical and morphological characteristics of the different clay minerals. The classification and nomenclature of these minerals is complicated by the existence of mixed-layer structures which are essentially epitaxial assemblages.

The utilization of clay minerals in grouting is discussed.

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 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.

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 brief description is given of modifications enabling high spacings to be observed.