In recent years, the availability of high-field superconducting magnets complemented with mechanical spinning of the samples (magic-angle spinning technique) has resulted in a considerable improvement in resolution of NMR spectra and has widened the use of this technique in the structural analysis of solid samples. In particular, NMR spectroscopy can distinguish the different chemical environments of tetrahedrally coordinated silicon and also determine short-range order in the distribution of Si and Al in micas (Sanz et al., 1983) and zeolites (Fyfe et al., 1983; Klinowski et al., 1982).

For aluminium (I = 5/2), the existence of strong quadrupolar interactions means that, in general, only the m½↔m−½ transition is observed. However, the signal is broadened by second-order quadrupolar effects, dipolar interactions and chemical shift anisotropies.

It is well established that palygorskite has an amphibole-like, double-chain structure. The linked tetrahedral groups forming continuous sheets are divided into ribbons of various widths due to alternation of the direction of tetrahedra which run parallel to the fibre axis (Brindley, 1980). This alternation of the chains leaves a series of holes of well-defined size which are filled with water molecules (channel water). Based on microscopic observations of cleavage surfaces (Bailey, 1980), the mineral appears to be built up of regular stacking of planes parallel to (h00) and (hk0) which form predominantly the surface of the laths parallel to the c-axis. This is further supported by the enhanced X-ray reflections from these planes. Some degree of structural disorder might be expected to result from the progressive elimination of the channel water on heating. In addition, the weak interchain bonding in palygorskite is likely to result in a shift of the layers parallel to the fibre axis.

Volcaniclastics have not as yet been considered prime hydrocarbon exploration targets. This is because they contain a high proportion of mechanically and mineralogically unstable components which generally cause a faster deterioration in reservoir quality upon burial than is found in siliciclastics. Also, their complex mineralogical composition makes the burial-related diagenesis more difficult to understand. However, under favourable circumstances—such as devitrification at shallow depth, leaching of unstable particles, fracturing, or reworking—volcaniclastics may act as good reservoir rocks. Both favourable and unfavourable case histories are discussed.

Hydrating high-alumina cement will react with calcium carbonate to form the complex mineral calcium carboaluminate hydrate, 3CaO.Al2O3.CaCO3.12H2O. This mineral is reported to be capable of providing strength in concrete and so may provide an alternative to the minerals normally found in the hydration of high-alumina cement, which may under certain conditions convert to other minerals with a loss in strength. Some doubt has been cast on the stability of calcium carboaluminate hydrate and it has been found that in hydrated high-alumina cement, calcium carboaluminate hydrate decomposes at temperatures in excess of 60°C. Cube compressive strength tests on high-alumina cement and high-alumina cement-calcium carbonate pastes have shown that the latter have a lower strength than pastes made with high-alumina cement alone. When cured at 50°C the high-alumina cement-calcium carbonate pastes show a loss in strength with curing time. Cements made with the high-alumina cement-calcium carbonate mixture always have a lower strength than those made with high-alumina cement alone and so no advantage is gained from their use.

Lors de l'étude du gonflement des smectites par analyse de la diffusion des rayons X aux petits angles, Pons et al. (1981) et Ben Rhaiem (1983) ont obtenu des diagrammes de diffusion caractérisés dans le domaine étudié par des modulations plus ou moins prononcées de la courbe d'intensité.

L'analyse quantitative des courbes de diffusion, et en particulier de ces modulations, permet alors de remonter à une description de la structure du gel ou de la pâte et aux relations existant entre texture et structure (Pons et al., 1981; Pons et al., 1982). La méthode générale d'interprétation proposée par Pons et al. (1981) repose sur une comparaison entre intensité expérimentale et intensité théorique calculée à partir de modèles.

The process developed in the UK to produce magnesium hydroxide from seawater is described, together with the heat treatment that the hydroxide receives to produce the active oxide. Some of the characteristics required of the dolomite used in the process are also discussed. Impurities introduced by the seawater are noted and the means by which they can be reduced explained.

Analytical transmission electron microscopy was applied to some authigenic chlorites occurring as grain coatings in sandstones. Compositional variation proved to be relatively slight: all were magnesian chamosites. The coating chlorites were often intimately mixed with extremely fine-grained (0·01–0·2 µm) hematite but analytical ‘contamination’ was avoided because of the very high resolution of both observation (spot location) and analysis. One example of a water-sensitive (‘swelling chlorite’) coating was also studied. This proved to have a very much more variable composition even within a single section. The coating appeared to include both chloritic and vermiculitic components. The effect of this on structural formulae is discussed and a model proposed in which the ‘talc’ layer may be common to both components.

Interpretation of downhole wireline logs is generally a major source of information used to build up a picture of the quality and distribution of reservoir rocks. Logging tools respond to a number of variables and comparison of a suite of different logs is usually required to isolate and identify the response due to a single factor, e.g. porosity or clay content. A new tool, the litho-density tool (LDT), has been used along with conventional logging tools in a mid-Jurassic sand/shale sequence. The LDT simultaneously measures Pe (effective photoelectric cross-section) and ρa (apparent bulk density). Pe is a function of atomic number which in turn reflects lithology or mineral composition. By using cross-plots derived from the LDT and other logs, patterns of mineral abundance are indicated.