Mineralogical and chemical heterogeneity within three standard clay mineral samples have been identified by X-ray diffraction and chemical analysis of various size-fractions. This heterogeneity is partly attributed to accessory minerals, but mostly to structural and compositional variations in the 2:1 layer minerals of different particle size in the same specimen.

Experimental studies of reactions between water and kaolinite, kaolinite + quartz, kaolinite + quartz + muscovite and natural kaolinitic mudstones (Jurassic Draupne Formation; Norwegian North Sea; Rhaetic Westbury Formation, SW England; Tertiary ball clay, SW England) at 50 MPa and 150°C or 200°C have demonstrated that quartz saturation can be achieved readily at 200°C At 150°C quartz saturation is achieved for natural mudstones, but not for mineral mixtures because of slow reaction kinetics. Geochemical solution modelling demonstrates coincidence between observed fluid compositions and those expected for the solid mineral assemblage. In addition to inorganic solutes, organic acid anions including citrate are reported as products in experiments with natural mudstones (especially the Draupne Formation). Fluids supersaturated with respect to quartz are unlikely to be developed from mudstones which lack smectites or amorphous silica.

Kaolin has been used as an alternative cheap raw material for the synthesis of zeolite 4A. Two steps are involved in the reaction: (1) dehydroxylation of kaolin at 550–900°C to form an activated X-ray amorphous material called metakaolin; (2) hydrothermal treatment of metakaolin with aqueous alkali to form the zeolite. The inherent colouring impurities in kaolin, especially the Fe minerals, affect the brightness of metakaolin and the resultant zeolite. The dehydroxylation temperature is found to have a significant influence on the kinetics of zeolite formation as well as on the brightness of zeolite. The present investigation deals with the preparation of metakaolins from a good quality kaolin at different temperatures and their characterization by XRD, IR, TGA, MAS NMR and brightness measurements. Hydrothermal reactions of these metakaolins with aqueous alkali have been conducted. The residual Fe in the mother liquor has been estimated. The improvement in brightness and change in reactivity of the metakaolin, difference in the kinetics of its conversion to zeolites and dissolution of Fe during zeolite formation have been correlated with the calcination temperature. A calcination temperature of 900°C (1 hr) is the optimum for this clay to change into a reactive metakaolin which gives detergent grade zeolite 4A of high crystallinity and maximum brightness.

La nacrite constitue le plus rare polytype des kaolinites. Traditionnellement, on attribue á ce minéral une genèse hydrothermale (Ross & Kerr, 1931; Hanson et al., 1981 ), cependant Btihmann (1988) décrit sa formation en condition normale de température et de pression dans des milieux de solution et de force ionique élevées. Dans ce travail, la nacrite est mise en évidence dans deux anciens gisements de Pb-Zn situés dans les massifs de Jbel Slata et Garn Halfaya au nord de la Tunisie (Fig.l).

The use of ground granulated blast furnace slag (ggbs) is well established in many cement applications where it provides enhanced durability, including high resistance to chloride penetration, resistance to sulphate attack and protection against alkali silica reaction (ASR). The use of ggbs in soil stabilization is, however, still a novel process in the UK although it has been used in South Africa. This paper reports on efforts to extend the use of ggbs to highway and other foundation layers by determining the beneficial effect which it has on the reduction of expansion due to the presence of sulphates. The paper describes the results of laboratory tests on lime-stabilized kaolinite containing different levels of added sulphate to which different amounts of ggbs have been added. The tests determine the strength development of compacted cylinders, moist cured in a humid environment at 30°C, and the linear expansion of these moist cured cylinders on soaking in water. The results illustrate that small additions of ggbs to sulphate containing clays which are stabilized with lime reduce substantially their expansion when exposed to water and have no significant deleterious effect on strength development.

The growth and decay rates of rapid, induced electro-optical phenomena in dilute colloidal suspensions are characteristic of the geometry of the solute particles. The speed of measurement renders such methods especially relevant for fast, in situ analyses of the size and size distribution of colloids in practical, industrial situations where these properties may be undergoing continuous change. The principles of the measurement of electrically induced birefringence using pulsed fields is outlined and used to study vermiculite suspensions as they undergo size reduction in an ultrasonic field. The high sensitivity of the method to both the particle size range and the form of the distribution function is indicated. The use of the method for on-line monitoring of dilute mineral suspensions for the indication and control of aggregated, dissolving or growing media is discussed.

Thermoporometry (TPM) was applied to hydrotalcite precipitates prepared with carbonate, bicarboxylic acids and chloride. It was used to measure the formation of an ice body between the hydrotalcite particles. Before TPM could be applied, the dried hydrotalcite precipitate had to be soaked for two weeks in water. The mean value of a factor F measured by TPM, which described the shape of the ice body in hydrotalcite, was 1.7. This value was between those of a purely cylindrical (F = 2) and a purely spherical ice body (F = 1), indicating the formation of ice lenses. From the radius of the ice body, Rn, ice volume, Vn and shape factor F, the corresponding specific surface area of the hydrotalcite particles could be assessed. The TPM indicated that the distance between the separate hydrotalcite crystals in water, which is equal to 2(Rn+0.9) nm, was a function of the type of anion incorporated at the interlayer, such as chloride and bicarboxylic acid. The pore volume and surface area of the hydrotalcite particles measured by TPM were compared with those determined by the traditional nitrogen sorption technique on dried hydrotalcite. It appeared that sorption of N2 yielded much lower values than TPM. This difference was interpreted as being due to slow penetration of N2 through the dried hydrotalcite samples to the interparticle voids.

La diffusion aux petits angles des rayons X (DPAX) a été utilisée pour caractériser l'évolution de la structure et de la texture d'argiles fortement hydratées en fonction de la température (Pons, 1980; Pons et al., 1981), de la concentration en sel (Saez et al., 1983) ou en fonction de la pression (Tessier, 1984; Ben Rhaiem et al., 1986, 1987). La méthode permet d'accéder aux paramètres structuraux du système par comparaison des courbes expérimentales à des courbes théoriques calculées à partir de modèles.

Porrenga (1968) described the green clays from the Lower Oligocene of Aardebrug, east of Leuven (Louvain) in Belgium as glauconitic illite, a mineral intermediate in chemistry between glauconite and illite, and presumed this clay to be neoformed, though the mode of origin is not discussed. Notably, most of the section from which Porrenga obtained his sample of 'glauconitic illite' is nonmarine. Non-marine glauconites are rare in the literature and there is no standard terminology. Parry and Reeves (1966) reported green pellets of 10 Å clay from recent sediments at Lake Mound, Texas, but with no detrital green clay as source and an authigenic origin is assumed. Green clays described as Fe-rich mica occur in lacustrine environments in the Oligocene of Cantal (Jung, 1954), and the Massif Central (Gabis, 1963) in France. These deposits are derived from altered crystalline basement.