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.

Current thinking regarding the possible origins and probable evolutionary histories of meteorites is summarized. Selected data concerning the composition, petrology and other characteristics of the CI and CM groups of stony meteorites in which layered minerals principally occur are then presented. Layered compounds, mainly phyllosilicates, are shown to form a major part of the fine-grained matrix of the CI and CM meteorites, which are classified as carbonaceous chondrites. The results of recent investigations of matrix mineralogy are reviewed, with particular emphasis on the findings of electron microscopy. Several forms of Fe-Mg-serpentine have been identified as the principal phyllosilicates. ‘Poorly-characterized phases’ in CM meteorites have proved to be tochilinite and intergrowths of tochilinite with serpentines. The results generally indicate that the phyllosilicates and most other matrix minerals formed by aqueous alteration in the regoliths of the CI and CM parent bodies; but there is isotopic evidence for the incorporation of components and possibly mineral grains which predate the solar nebula. It is concluded that more detailed chemical and mineralogical information about the phyllosilicates and associated minerals will enable useful constraints to be placed on the possible identities of their precursors and the environments in which both they and the matrix minerals formed.

The weathering of two co-existing sodic (glaucophane) and calcic (actinolite) amphiboles in a glaucophane-schist was studied by optical microscopy. XRD and the electron microprobe. In the early stages of weathering, two trioctahedral expandable phases occur as internal weathering products in the amphiboles: a sodic saponite in the glaucophane and a calcic ‘hectorite’ in the actinolite. Further weathering leads to the replacement of the ‘hectorite’ by a calcic saponite in the actinolite, while the saponites formed in the weathered glaucophane exhibit progressive calcium enrichment in their interlayer sites. These observations demonstrate the influence of the primary mineral compositions on initial weathering products.

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.

Sixteen glauconite samples from different locations in Belgium and Northern France were investigated by 57Fe Mössbauer spectroscopy at room temperature. The spectra were fitted with three Fe3+ and two Fe2+ doublets, both Fe species occupying M1(trans) and M2(cis) sites in the T-O-T layers. The third Fe3+ doublet was assigned to interlayer ferric complexes. The observed Mössbauer parameters did not show significant variations from sample to sample. No direct relation between K and Fe content was observed, although within some distinct groups (e.g. Bande Noire, Cenomanian) the amount of Fe2+ increased with increasing K content.

Interstratified illite-smectites from Carboniferous sediments from the Alston and Askrigg blocks and the intervening Stainmore trough of the northern Pennines, UK, were examined by XRD. Both blocks are underlain by Caledonian granites. During late Carboniferous times sediments overlying the Alston block were intruded by the Whin Sill. The percentage smectite in illite-smectite (%S in I/S) varies from ∼35% to <5% only homogeneous mudstones give consistent results. In the case of the Askrigg block and Stainmore trough, a good inverse correlation was found between %S in I/S and vitrinite reflectance. Both illitization of illite-smectite and vitrinite reflectance increase towards the centre of the block. This is thought to be related to high heat-flow centred about the granite basement. In the case of the Alston block, there is no direct relationship between clay and vitrinite data, vitrinite reflectance being controlled by the position and thickness of the Whin Sill. Except where close to the contact, the Whin Sill had no apparent effect on %S in I/S. As observed for the Askrigg block, %S in I/S is directly related to the position of the underlying granite. The progressive illitization of illite-smectites of low expandability is very slow when compared to vitrinite alteration in response to rapidly increasing temperature. Consequently, %S in I/S is a potential indicator of thermal maturation in situations where vitrinites, by virtue of their rapid response to increasing temperatures, fail to provide a regional view of heat-flow patterns.

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.

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.

Smectites were synthesised hydrothermally from zeolites in an Mg-rich brine at 300°C under a confining pressure of 30 MPa and characterized by XRD using the Greene-Kelley Li-saturation test and the K+-saturation/glycolation test. The synthetic smectites were found to be dioctahedral with only tetrahedral negative layer charge; the layer charge was also deduced to be low and they are classified as beidellites. The mechanism of formation includes H+ saturation of zeolites by the hydrolysis of Mg2+ under hydrothermal conditions, followed by decomposition of the zeolites and recrystallization to beidellites. These results show that solution chemistry is an important factor affecting stability of zeolites under hydrothermal conditions.

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.

Copper-sepiolites exchanged at different levels have been studied by ESR, IR, and TG. The results indicate that in the unheated samples the Cu2+ ions are located in octahedral edge positions. After dehydration, the Cu2+ ions occur in two positions with different environments. Some of the Cu2+ ions lose the two molecules of coordinated water in one step, at low dehydration temperatures, and adopt a square pyramidal geometry. Other Cu2+ ions lose the coordination water in two steps, at lower temperature than the natural sepiolite, and adopt a tetrahedral symmetry.

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.

Marine clays of SE Norway lifted above sea-level have been subjected to weathering for 8500 years. As a result of this weathering a major part of the quartz, K-feldspar and plagioclase disappeared in the 0·2–0·6 µm fraction. Trioctahedral illite passed through the sequence: illite → mixed-layer illite-vermiculite → vermiculite → dissolution. This transformation started at a depth of 3 m, and the 2:1 layers dissolved in the upper part of the profile. Chlorite was broken down by weathering into finer particles. As a result, chlorite was first removed from the coarser fractions. Dioctahedral illite in the clay fractions passed through the following transformations in the upper part of the profile: illite → mixed-layer illite-vermiculite → vermiculite → chloritized vermiculite. Weathering models for the size fractions 0·2–0·6 and 0·2–2 µm showed that total amounts of dissolved material from these fractions in the upper part of the profile could be calculated as 55 and 38%, respectively. Dioctahedral 2:1 layers were most resistant to weathering, resulting in 75% dioctahedral phyllosilicates in the 0·2–0·6 µm fraction in the uppermost part of the profile, in contrast to 30% dioctahedral illite in the unweathered sample. This study illustrates the importance of investigating different fractions and not only material finer than 2 µm.

Le mécanisme de rètention de l'octylbenzènesulfonate de sodium (OBSNa) en milieu aqueux pur sur les argiles correspond essentiellement à une précipitation du sel de calcium (OBS)2Ca. L'adsorption, proprement dite, atteint à peine 2 à 3 µEq/g d'argile. En présence de KCl, la part de l'adsorption devient plus importante à cause de l'augmentation de la solubilité du sulfonate de calcium. L'affinité des monomères du tensio-actif pour l'interface solide-liquide est accrue. On montre que l'adsorption varie avec les propriétés de l'argile, en particulier, avec le nombre et la nature de ses cations échangeables. L'équilibre d'adsorption dépend de l'état d'avancement des réactions d'échange entre les cations échangcables de l'argile, les cations apportés par l'électrolyte (KCl) et le monomère (Na+), et les cations adsorbés sur les micelles. II existe, pour chaque argile, une concentration limite en KCl, d'autant plus grande que la teneur en calcium de l'argile est élevée, et à partir de laquelle le tensio-actif ne précipite plus. La rétention se fait alors uniquement par adsorption. Suivant les conditions de pH, elle a lieu sur les cations échangeables de l'argile et les sites positifs à la périphérie des cristaux (kaolinite) ou seulement sur les cations échangeables (illite et chlorite). Dans les procédés de récupération assistée du pétrole, l'addition de chlorure de potassium au fluide de balayage permettra de réduire la précipitation du tensio actif. Même, si l'adsorption augmente, cet effet est souvent suffisant pour que, globalement, la rétention diminue.

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.

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.

A simple IR spectroscopy method for detecting hydrated and dehydrated halloysite in artificial mixtures with kaolinite is described. The method is based on the exclusive ability of RbCl among the alkali halides to form a complex with halloysite but not with kaolinite. This complex absorbs at 3500 cm−1 when hydrated halloysite or admixed halloysite is examined in RbCl disks, the limit of detection being 15% in the kaolin admixture. Heating the clay powders or corresponding RbCl disks at 110°C affects the 3500 cm−1 frequency. The development of this absorption band together with a decrease in the intensity ratio of the 3690/3620 cm−1 frequencies is proportional to increasing amounts of halloysite in the kaolin admixtures. This method has an analytical applicability and is relatively rapid.

The Wash drainage basin contains four principal river systems. Samples were collected from the freshwater and estuarine reaches of each of these, and silt- and clay-grade fractions were separated and examined by XRD. The clay mineralogy of each of the rivers is different; in the north the Witham sediments contain chlorite, the Welland and Nene samples contain vermiculite, with a higher proportion of kaolinite in the former, while in the south the Ouse sediments contain smectite. The clay fractions of the samples from the estuarine reaches all contain chlorite, confirming that non-fluvial sources must contribute to the sediments of the Wash. Comparison of this pattern of clay mineralogy with that for the underlying Jurassic and Cretaceous rocks shows that there was relatively little modification during the Pleistocene glacial periods. Such a pattern supports recent work which suggests that ice moved through the Wash gap and then fanned out from the Fenland area, rather than entering the region from the north.

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.