Les propriétés d'hydratation de phlogopites altérées-(Na,Ca) et -(Na,K) sont étudiées á l'aide des techniques de diffraction des rayons X. La comparaison du diagramme calculé d'après un modèle mathématique au diagramme expérimental permet de mettre en évidence un phénomène de démixtion des cations dans les espaces interfoliaires. Cette ségrégation est plus importante dans le cas des échantillons -(Na,K) que dans celui des échantillons -(Na,Ca). Une analyse quantitative du phénomène montre l'existence d'une ou de deux phases cristallines distinctes selon les teneurs en calcium ou en potassium. Les proportions relatives de ces deux phases ainsi que la composition de leurs espaces interfoliaires ont été déterminées. Un mécanisme élémentaire est proposé; il explique la présence et la composition de ces différentes phases.

A procedure is described for the quantitative estimation of hematite, goethite and lepidocrocite in soil clays by differential X-ray diffraction combined with profile refinement. The method has been applied to clays from 12 palaeosol horizons from south-east England. Samples containing as little as 1% dithionite-extractable iron can be analysed in this way. The hematite: goethite ratio is determined to within ±3% for soil clays having ∼2.5% of each oxide and to within 10% in less favourable cases. The concentration of oxides in the soil determined solely from X-ray diffraction and from a combined chemical analysis/X-ray method are in good agreement. In addition to improving the accuracy and extending the range of iron-oxide concentrations over which analysis can be carried out, the method may, in principle, be used to provide information about the cell parameters and line profiles of each component present.

Aniline, adsorbed from aqueous solution in 1% (w/v) clay suspensions, forms coloured complexes and polymerizes on Fe(III)- and Cu(II)-montmorillonite. As evidenced by the adsorption isotherms, and the coloration and spectroscopic (IR, ESR) characteristics of the organo-clay associations formed, the conditions under which these reactions take place and the mechanisms involved differ according to the exchange cation. Fe(III) interacts with the π electrons of the aromatic ring to give rise to radical cations or so-called type II complexes, provided the aniline concentration does not exceed 500 p.p.m. With Cu(II). an aniline concentration above 500 p.p.m. is required and the reaction occurs at the amine group, proceeding through coordination followed by free-radical formation.

A detailed study of the mineralogy of the Jurassic detrital sediments of the Betic Cordillera (SE Spain) was needed to resolve problems relating to the environment of deposition. The choice of the marly limestone and marl facies for such a study was appropriate, because these are well represented throughout the Cordillera and consist of the earliest materials deposited after the break-down of the Liassic carbonate platform. Quantitative mineralogical analyses and crystallochemical studies enabled the source area to be defined, as well as indicating the likely erosion and weathering processes undergone by the minerals during transport and deposition, and the degree of diagenesis. Four mineral associations were distinguished, permitting a temporal and spatial analysis of the environment of deposition, and the relationship between its mineralogy and the different lithological facies.

Le remplissage des cavités karstiques de la région d'Ain Khamouda (Tunisie Centrale) est partiellement constitué d'une argile blanche. Son étude par diffraction X. ATD et analyse chimique traditionnelle montre qu'il s'agit d'un mélange d'halloysite prédominante et de smectite, renfermant plusieurs pourcents de ZnO. Une étude plus détaillée mettant en oeuvre un diffractométre à détecteur linéaire et à ambiance contrôlée, la microscopie électronique à transmission et la microscopie électronique à transmission en balayage (STEM) a permis de préciser les points suivants. En dehors de l'halloysite totalement dépouvue de zinc, il existe deux phases porteuses de ce métal: une sauconite et un hydroxyde de zinc à peu près amorphe. En outre, les faibles quantités (0.2%) de MgO contenues dans l'échantillon sont localisées à l'intérieur des tubes d'halloysite. De plus, ce minéral est présent sous la forme de deux phases, l'une hydratée, l'autre anhydre. Enfin, ces argiles renferment un peu d'argent sous la forme de microparticules de 3 à 10 nm de diamètre.

Diagenetic chlorite is forming as a result of temperature-controlled burial diagenesis in shales from the Sleipner area of the North Sea. Accompanying chlorite diagenesis, kaolinite and illite-smectite decrease in abundance, and illite increases in abundance. These clay mineral transformations occur between 122–126°C at temperatures higher than normally expected for chlorite diagenesis. Kaolinite and ordered illite-smectite are largely unaffected by diagenesis below 100°C. It is proposed that chlorite diagenesis is thus delayed due to the absence of a source of ions resulting from smectite decomposition. Clay mineralogy is of no lithostratigraphic use in the Jurassic sediments of the Sleipner area. However, the zone of chlorite diagenesis is a reliable indicator of maximum burial temperature.

The fluorination of montmorillonite by aqueous ammonium bifluoride solution (NH4HF2) has been investigated by chemical, sorptive, porosimetric and electron microscopic methods. Changes in the chemical composition of the montmorillonite during the fluorination were compared both in the crystal surface and in the bulk sample. The accumulation of fluorine was distinctly zonal, being present mainly in the surface layers. The electron microscope studies showed that the 300–400 nm thick macrodomains in the initial montmorillonite were cracked into small microdomains 20–30 nm in thickness, this resulting from disruption in the continuity of the octahedral sheets. These distinct changes in morphology of the montmorillonite aggregates particularly influenced the porosity and sorptive properties.

L'altération latéritique débutante des orthopyroxènes et clinopyroxènes de Niquelandia, Brésil, montre plusieurs stades. Le premier stade facultatif est la formation de produits ‘amorphes’ dont la composition chimique proche de celle des minéraux parentaux, montre déjà un enrichissement en nickel. Le deuxième stade est marqué par l'apparition de phyllosilicates dont la nature et la composition chimique varient selon le degré de porosité de la roche parentale. Cette porosité contrôle également la distribution du nickel dans les différents phyllosilicates, (saponite, talc, pimélite). Les pyroxènes ne contenant pas ou très peu de nickel, il est clair que le nickel qui s'accumule dans les produits de l'altération est totalement importé avec les eaux de percolation. L'origine de ce nickel est à rechercher plus haut dans les profils ou plus en amont dans la séquence, là où les dunites sont présentes.

The mineralogy of the fine clay fraction (<0·2 μm) of two soil pedons (Aquic and Udic Haplustalfs) representing the wheat-sugarcane belt of the Indo-Gangetic alluvial plain was studied by X-ray diffraction, differential thermal analysis, transmission electron microscopy, and by chemical analysis. The XRD patterns are characterized by unusually high spacings which are interpreted in terms of an interstratification comprising smectite, illite and ‘chlorite’ components. The CEC data (Ca/Mg and K/NH4) also indicate the possible presence of vermiculite. A plateau bridging the 7–10 Å maxima in K-saturated specimens heated at 300°C suggests interstratification of kaolinite and smectite, although this may not be part of the above interstratification. The diffuse bands shown by Mg-glycerol-solvated Ap-horizon clays at ∼21 Å, and the increasing elimination of XRD peaks in the > 10 Å region with distance from the surface, suggests that the expanding layers have a slight tendency to segregate in Ap horizon samples and that randomization tends to increase with depth. Discrete illite and small amounts of kaolinite were also detected.

L'analyse semi-quantitative, avec une microsonde électronique CAMEBAX, met en évidence des variations chimiques significatives dans des assemblages simples de minéraux argileux. La méthode est décrite et deux applications sont présentées et interprétées en termes de genèse et de paléoenvironnement. La microgéochimie d'illites et de chlorites du Crétacé inférieur (Marge du Maroc) évolue vers le haut de la série (diminution du magnésium) et semble influencée par une diagenèse salifère transformant des argiles détritiques. Des chlorites hypermagnésiennes apparaissent dans les sédiments les plus profonds, et autorisent l'hypothèse d'une authigenèse en milieu confiné. Les différentes smectites étudiées a la limite basalte-sédiment des sites 105 et 384 du DSDP (NW Atlantique) peuvent aisément être distinguées par leur microgéochimie avec Mg, Na, K, Al, Fe, Ti. Elles reflètent diverses sources volcaniques et leurs caractères sont très différents de ceux des smectites terrigènes communes.

Dark blue-green Fe(II)Fe(III) hydroxychlorides and -sulphates were described by Feitknecht & Keller (1950) and later by Bernal et al. (1959). To further understand the formation and transformation of these compounds, Taylor & McKenzie (1980) and Taylor (1980) prepared Fe(II)Al(III) and Fe(II)Fe(III) hydroxychlorides, -sulphates and -carbonates by a more controlled hydrolysis reaction. These compounds, referred to as ‘green rusts’ by Bernal et al. (1959), are isostructural with hydrotalcite. However, the X-ray diffraction patterns can vary with the M(II)/M(III) cation ratio as it departs from the ideal value of 3, and with the interlayer anion.

Studies of the thermal stability of organic compounds adsorbed on clay minerals are of interest from several points of view, e.g. the type and strength of bonding forces between the organics and the clay surfaces (Chou & McAtee, 1969; Yariv et al., 1971; Lacher et al., 1981), and the effect of the clay surface on stability or degradation mechanism of the organic compounds adsorbed on clays (Bodenheimer et al., 1966; Yariv et al., 1971; Durand et al., 1972).