Sixteen montmorillonites (8 normal and 8 abnormal using DTA dehydroxylation criteria) from the Gurasada bentonite deposits, Romania, were investigated by ESR. The spectra showed two features: a g = 4·3 signal attributed to isolated Fe3+ ions and a broad resonance with g ∼ 2·0 which was interpreted as arising from exchange interactions between clusters of Fe3+ ions. Additional experiments suggested that the latter resonance could have a structural component. The line-shape of the two resonances varied between normal and abnormal montmorillonites, indicating that the distribution of the Fe3+ ions between internal phase (montmorillonite lattice) and external phase (montmorillonite surface) was different for the two varieties.

The alkylammonium adsorption method for the determination of layer-charge density was slightly modified and applied to mixtures of expandable clay minerals (i.e. predominantly 18 Å minerals after glycerol sorption) from two loess samples and two soils (Haplaquept and Aquentic Chromudert) having different K-adsorption properties. The layer-charge density of the so-called 18 Å minerals from these sediments and soil samples varied between −0·23 and −0·85 per formula unit, which suggested the presence of different amounts of vermiculite within the 18 Å minerals. The amounts of these vermiculites were related to K-fixing and K-buffering properties of the different samples. High-resolution electron micrographs of vermiculites saturated with tetradecylammonium exhibited a basal spacing of 25 Å. It was confirmed, that the alkylammonium ions in the interlayers of the vermiculites formed a paraffin-type structure. In the fine clay from the loess samples an interstratification of vermiculite and illitic layers was observed.

Comparative porosity studies based on nitrogen sorption isotherms were carried out on six freeze-dried Na-montmorillonites (Moosburg, Camp Berteau, Marnia, Greek Yellow, Greek White, Wyoming bentonite), untreated and deferrated with dithionite/citrate. Mesopore analysis was carried out using the ‘parallel-plate model’; for supermicropores the ‘MP’ method was used. Most of the surface area was located in the supermicropores (width 7–15 Å). Higher total surface areas of the deferrated clays resulted from a much higher supermicroporous surface area, while the mesopore surface was similar or smaller. The lower the charge density of a subfraction of deferrated Wyoming (Na-)bentonite, the lower the vapour pressure at which the interlamellar sorption of ethanol occurred. The results predict an expansion on contact with the first traces of ethanol at 298 K for a Na-smectite with a charge density ξ = 0·11 e/(Si,Al)4O10 unit. Compared with ethanol, methylbromide showed a weaker interaction with Na-smectite. At p/p0 = 0·4 only 18 % of the interlamellar zones of low-charged Laponite were penetrated; one third of the supermicropores of this smectite were not accessible to CH3Br.

Deux questions sont abordées: (1) Une eau naturelle étant donnée, peut-on considérer qu'elle est en équilibre avec un minéral de formule connue? (2) Un ensemble homogène d'eaux naturelles étant donné, peut-on considérer que ces eaux sont en équilibre avec un minéral? Si oui, Peut-on proposer une estimation de la composition de ce mineral? Nous proposons une méthode pour répondre à chacune de ces deux questions. Cette methode est appliquée à l'estimation de minéraux argileux de formule générale SiaAlbMgcCadKeNafOn(OH)m. Les données utilisées sont des eaux de percolation, dans des colonnes de sols.

The applicability of 27Al and 29Si magic-angle-spinning nuclear magnetic resonance (MASNMR) spectroscopy to the investigation of order-disorder in 1 : 1 dioctahedral layer-silicates was tested. 27Al and 29Si MASNMR showed the existence of short-range order in all these systems while XRD showed different degrees of long-range order-disorder. Spectra obtained on kaolinite and metakaolin clearly showed the transformation of some octahedral Al in kaolinite to tetrahedral coordination in metakaolin and also showed short-range Al and Si disorder in the latter. This suggests that structural re-arrangement on thermal treatment can be monitored by this technique. These results further suggest that MASNMR can detect short-range order, which is complimentary to the information that XRD provides regarding long-range order.

Present-day marine sediments around the emerged basaltic areas of Iceland and the Faeroe Islands are characterized by the abundance and predominance of smectites. Smectites increase regularly and systematically near volcanic areas. Their origin from (i) meteoric/deuteric weathering, (ii) hydrothermal products, (iii) neoformation in the marine environment or (iv) transformation during their transport to or stay in oceanic regions is considered in a comparative study of three types of environments on or near the Faeroe Islands. These are (1) a basaltic environment where phyllite minerals of deuteric and hydrothermal origin are abundant; (2) a soil environment formed on basaltic flows; (3) a marine sedimentary environment within adjacent sedimentary basins. This investigation clearly shows the link between hydrothermal and deuteric saponite-celadonite in basalt, Fe,Mg-smectite in Faeroe soils and Fe-smectite in marine sediments.

Dans le cadre de l'étude de l'interaction eau-kaolinite, des mesures de conductivité (pertes diélectriques) et de permittivités réelles ont été entreprises à fréquence variable (103–107 Hz) et en fonction de la température (27–80°C). La conductivité croît avec la fréquence et la température de mesures. L'utilisation d'un modèle de conduction par déplacement de protons par sauts discrets entre sites localisés est applicable. La loi σ′(ω) ∼ Aωs est vérifiée. L'évolution du paramètre s en fonction de la pression de vapeur d'eau permet de déterminer le mécanisme d'établissement de la monocouche d'eau sur le solide. La permittivité réelle décroît avec la fréquence. C'est une fonction croissante de la pression de vapeur d'eau. Un calcul simple permet de retrouver la loi expérimentale relative à la permittivité ɛ′ ∼ exp(K√P).

Nickel crystal chemistry was systematically studied in various phyllosilicates, mainly the natural phases selected from the ‘garnierites’ of the supergene ore deposits of New Caledonia. Minerals which do not usually occur in New Caledonian parageneses were synthesised, as they could represent intermediate phases of genetic importance. In the kerolite-pimelite series, a linear relationship occurred between the ratio I(13,20)/I(02,11) of the hk bands and Ni-content. Diffuse reflectance spectra were used to derive the crystal chemical parameters of Ni. These confirmed its divalent character and its occupation of octahedral sites; the resulting structural distortion was slight and could not be detected in some minerals. There was no optical evidence for Ni atoms in 4-fold coordination. The two main parameters which showed significant variations among the studied phases were site distortion and crystal field stabilization energy (CFSE). Site distortion was at a maximum in trioctahedral smectites and sepiolite. CFSE depended on the mineralogy, crystallinity and chemical composition (Al-content) of the phase. Finally, clay minerals are classified according to the increasing stability of Ni in the octahedral sheet, which has been tentatively related to the geochemical distribution of this element. Secondary minerals are usually enriched vs. primary ones and among them are nepouite and kerolite which exhibit a high CFSE in contrast to sepiolite.

A trioctahedral, ferrous smectite has been located in the uppermost deposits of Atlantis II Deep, SW basin, Red Sea. This clay is very unstable when removed from its environment of formation and, for example, oxidizes during desiccation under laboratory conditions. Only X-ray transmission diffraction study of the mud itself demonstrates the trioctahedral character of the clay. Electron-optical investigation shows that oxidation within the octahedral sheet creates a juxtaposition of dioctahedral and trioctahedral sub-lattices in the same particle. Ferrous smectite authigenesis is located near the hydrothermal spring outlets of the Atlantis II Deep.

The presence of palygorskite in soils and sediments of the Middle East countries has been widely reported: in Syria (Muir, 1951), Israel (Yaalon, 1955; Barshad et al., 1956; Ravikovitch et al., 1960; Singer, 1971; Singer & Amiel, 1974; Yaalon & Wieder, 1976), Iraq (Al-Rawi et al., 1967; Eswaran & Barzanji, 1974), Lebanon (Lamouroux et al., 1973), Jordan (Wiersma, 1970; Shadfan, 1983; Shadfan & Dixon, 1984; Shadfan et al., 1985) and Saudi Arabia (Aba Husayn & Sayegh, 1977; Elprince et al., 1979; Mashhady et al., 1980; Viani et al., 1983; Lee et al., 1983; Mackenzie et al., 1984; Shadfan & Mashhady, 1985). In Egypt, Elgabaly (1962) indicated the predominance of palygorskite in some of the soils in the western desert and proposed that the mineral had formed from calcareous argillaceous material in a saline lagoon. Hassouba & Shaw (1980) found palygorskite to be a major component of the clay fraction in caliche crusts in the coastal plain of north-western Egypt and considered that the palygorskite had formed authigenically in that environment.