Les auteurs étudient les produits de l'altération fumerollienne et météorique de Vulcano, Iles Eoliennes, Italie. Ces produits sont étudiés par diffraction des rayons X, analyse chimique classique, microscopie électronique et microsonde.

The Alto dos Quintos Mine, Rio Grande do Norte, northeast region of Brazil, is one of the few mines where a LCT (Li-Cs-Ta-enriched) pegmatite is exploited for the deep blue gemstone called “Paraiba Tourmaline (PT)”. Blue cuprian elbaite, a fault-bound pink montmorillonite bearing some relict apatite and newly-formed Ca-Al-phosphate of the Al-P-sulphate group (APS minerals) also occur in the underground mine. The montmorillonite was studied using extended clay mineralogical tools (XRD, IR spectroscopy, XRF, SEM-EDX, cation exchange capacity (CEC), DTA). The structural formula method for calculation of the smectite formula based on EDX data yielded an extremely Fe-poor montmorillonite: (Ca0.22+)(Al1.7Fe0.0Mg0.4)(Si3.8Al0.2). The charge on the tetrahedral sheets accounts for approximately 30% of the total permanent negative charge. However, based on the more precise Hofmann & Klemen test, tetrahedral charge values of 11% to 13% were calculated. This is indicative of the dominance of montmorillonite rather than beidellite among the smectite minerals, which is independently proved by a pronounced IR band at 630 cm-1. The formation of pink montmorillonite is not directly related to the emplacement of the Li-bearing PT pegmatite. The sheet silicate developed after a considerable hiatus (Mesozoic?), when the Neoproterozoic pegmatites had already undergone different stages of hypogene (cookeite) and supergene (illite, kaolinite) alteration, during which Li was flushed out to a degree that formation conditions of expandable Li-bearing phyllosilicates were no longer favoured. The nature of the pinkish tint is not yet clarified. The montmorillonite formed in a temperature regime close to 250°C, when apatite was transformed into Ca-bearing APS minerals under acidic conditions. Cainozoic volcanic activity and the reactivation of deep-seated fault zones are considered to be responsible for the formation of this pink P-bearing montmorillonitic clay.

The present study explores the effect of a magnetically modified halloysite (mHNT) surface on the structure and properties of biodegradable polymer nanocomposites based on poly ɛ-caprolactone (PCL). Halloysite nanotubes (HNTs) have been modified by a scalable and tunable procedure using magnetic Fe oxide particles prepared by microwave-assisted synthesis fromferrous sulfate at high pH. The HNT content in composites prepared in melt varied from 5 to 30 wt.%. Application of magnetically modified HNT to PCL resulted in the formation of soft magnetic materials. Analyses of the nanocomposite structure revealed that both natural and magnetized HNTs, as well as free magnetite particles are dispersed uniformly in the polymer matrix. Investigation of the mechanical and physical properties confirmed that the reinforcing ability of HNTs was not affected by magnetic modification.

This study evaluates the rare earth element (REE) geochemistry in altered trachyandesitic ignimbrites, tuff and lava flows in the Hashtjin area by assessing chondrite-normalized REE patterns and Y/Ho geochemical ratios. Modifications in the REE patterns took place along altered fault zones that were affected by hypogene and supergene alterations. The precursor volcanic and pyroclastic rocks contain phenocrysts of plagioclase accompanied by augite, zircon, apatite and pyrite. Based on X-ray diffraction analysis, the main mineral assemblages of the altered units consist of kaolinite as the main clay mineral, SiO2 polymorphs (quartz and cristobalite) and anatase as a minor constituent. The chondrite-normalized REE patterns of argillic samples reveal fractionation of light REEs (LREEs) compared to heavy REEs (HREEs), together with a marked Eu anomaly and a weak W-type tetrad effect related to the weak non-charge radius control (CHARAC) behaviour of REEs and slightly higher Y/Ho and Zr/Hf ratios. The relationship between the Y/Ho and Zr/Hf ratios and recognizable T3 and T4 effects (tetrad effect) suggests that an increasing degree of water–rock interaction occurred during hypogene alteration processes by acidic hydrothermal fluids that were overprinted by supergene alteration. Water–rock interaction and adsorption by Mn-oxides and clay minerals are considered to have played important roles in determining the close to non-CHARAC behaviour of REEs during the argillic alteration of the pyroclastic rocks in the Hashtjin area.

A montmorillonite clay and an X-ray amorphous Fe(II)-silicate were suspended in a synthetic groundwater solution under oxic and anoxic conditions at 23 and 70°C for 200 days. The clay samples were then analysed for total Fe, Fe(II), dithionite- and oxalate-extractable Fe (Fed and Feo), cation exchange capacity (CEC), and examined by X-ray diffraction (XRD) and diffuse reflectance spectrometry (DRS). The total iron content and Fe(II)/Fe(III) ratio of the clay increased with an increase in temperature and both were greater under anoxic than oxic conditions, as were the amounts of Fed and Feo. The CEC of the clay was lower in the presence of the Fe-silicate, suggesting that Fe-hydroxide had precipitated at the edges of the clay blocking some cation-exchange sites. No changes in the clay were detected by XRD or DRS after contact with the Fe-silicate, nor was there any evidence for Fe-hydroxide material in the interlayer region of the clay. However, it is shown that the amount and nature of iron associated with clay can be significantly altered and certain properties of the clay, such as CEC, can be affected when the clay is in contact with Fe(II)-containing materials.

Examination of rock samples from Job's Hill, St Mary, Jamaica, by chemical, X-ray, differential thermal, and infrared analyses showed predominant dickite with associated nacrite and kaolinite. The uniqueness of this deposit makes it possible that selected material could be used as a standard mineral.

Fourth-order relative sea level changes may have a significant impact upon burial diagenesis and reservoir quality through their effect upon surface and subsurface temperature. Relative sea level changes can induce sediment surface temperature changes of <20°C when the sediment surface changes from being close to or beneath the thermocline to being sub-aerially exposed. Such sea level changes typically occur on a timescale of half a million years. Approximately one quarter to one third of the magnitude of these temperature fluctuations will be propagated to 2500 m in the subsurface. Shorter timescale fluctuations of similar magnitude, resulting from glaciation, will not be significant below ~1000 m burial as there is not enough time to effect the change before the next surface temperature cycle occurs. Diagenesis is strongly controlled by temperature through its impact on the driving force and rate of geochemical processes. Burial diagenesis and cementation may thus be episodic on timescales associated with sequence stratigraphic events occurring on the surface, thousands of metres above the zone where diagenesis is occurring.

Samples of ‘blue clay’ were distributed among nine laboratories in various countries to assess the possibility of quantitative mineralogical determination. The disordered form kaolinite commonly found in fireclays and illite, or mica, were found by all laboratories, as was a material variously described as montmorillonite, swelling material (vermiculite, beidellite or open illite), or intermediate or swelling illite. The next most abundant mineral was quartz. Opal, chlorite, felspar, anatase, and organic matter, all in small quantities, were not all found by any laboratory and traces of calcite and dolomite were observed in one only. The most effective procedure is discussed, and it is concluded that the results are of a semi-quantitative rather than a quantitative nature.

In order to determine the relative influence of palaeoenvironmental and diagenetic processes in clay assemblages, as well as their significance, both fine- and coarse-grained sediments from the Campo de Gibraltar flysch have been studied by means of X-ray diffraction, optical and electron microscopy, and chemical analysis. Diagenetic modifications appear to be lithologically controlled and mainly affect coarse-grained sediments, where Fe-chlorites, illite and kaolinite are the more characteristic authigenic clay minerals. The evolution of detrital assemblages, determined in fine-grained beds, indicates that, from Cretaceous to Eocene times, clay mineralogy, characterized by the opposite kaolinite+smectite and illite + I-S mixed-layer assemblages, was mainly controlled by sources, climate and transport processes. On the other hand, from the Oligocene, clay mineral assemblages, characterized either by the abundance of kaolinite, or by the illite+chlorite association, mainly reflect the petrology of source rocks, as a consequence of climatic cooling and the increasing tectonic activity, which impede the development of soils.

La décarboxylation de l'acide oxaloacétique en acide pyruvique a été étudiée en présence de montmorillonite saturée en cations différents et des mêmes cations à l'état libre (non incorporés). L'action catalytique dépend de la nature du cation, cést-à-dire de sa facilité à former des complexes avec l'acide oxaloacétique. Le réseau argileux intervient dans la catalyse essentiellement par les atomes d'aluminium (ou de fer) situés sur les bords des feuillets argileux. Il joue le rôle d'un métalloenzyme biologique. Le calcul des énergies d'activation pour les différents systèmes met bien en évidence l'activité catalytique de l'argile. En présence du phyllosilicate, la réaction a lieu avec un bon rendement jusqu'à une température de 60°C.

Talc is very often an important constituent of suspended matter in marine and lacustrine environments but is rarely detected in sediments. The presence of talc is usually attributed to its industrial and agricultural application. Its recent anthropogenic use, long residence time in the water column due to its small particle size, transport by surface currents and winds, and its tendency to resuspension from the sediment are factors which contribute to the preferential detection of talc in suspended matter.

Much emphasis has been placed recently on the role of Ostwald-type processes (both ripening and the step rule) in the formation of interstratified illite-smectite clay minerals during diagenesis. Closer investigation of the relationships between illite particle thickness (as defined in terms of the fundamental particle theory) and particle chemistry show that simple Ostwald ripening is too simplistic a mechanism to describe observed changes in illite thickness and composition. In addition, available thermodynamic data on clay minerals suggest that the conventional notion of metastability associated with Ostwald's step rule is an inaccurate description of the relationship between illitic clay minerals and their macroscopic 2 : 1 phyllosilicate analogues.

Green rusts, GRs, can act as both sorbents and reductants towards selected pollutants. Organo-GRs are expected to combine these properties with a high affinity for hydrophobic substances. A novel organo-GR, GRLAS, was synthesized by incorporating a mixture of linear alkylbenzenesulphonates (LAS) into the interlayer space of synthetic sulphate green rust, GRSO4 . Mössbauer analysis of GRLAS indicates that the structure of the organo-GR is very similar to that of the initial GRSO4 with regard to the FeII/FeIII ratio and local coordination of Fe atoms. X-ray diffraction demonstrates that the GRLAS formed was well ordered, although a mixture of surfactant was used for intercalation. The basal spacings of the GRLAS and the kinetics of the ion-exchange process were dependent on the initial surfactant loading; basal spacings of ~2.85 nm were obtained at LAS solution concentrations >10 mM. The ratio LASadsorbed/SO42–desorbed significantly exceeded the stoichiometric ratio of 2 during the initial part of the ion-exchange process (t = 5 h). However, this ratio was reached progressively with time. GRSO4 preferentially sorbed LAS homologues with long alkyl chains over short ones. Carbon tetrachloride was successfully adsorbed into GRLAS. The adsorption isotherm was linear with a distribution coefficient, Kd, of 505±19 litre kg–1.

Fluorescence and phase transitions of a new Mg-Al-Eu ternary layered double hydroxide (LDH) and their dependence on thermal treatment were studied for the first time. Phase transitions occurred as the temperature increased from 400 to 1100°C. The process of phase transition is discussed in detail. The emissions of Eu3+ ions described by the 5D0–7FJ transition (J = 1,2,3,4), and especially for the 5D0–7FJ transition (J = 1,2) varied markedly with phase transformations from LDH, MgO, to mixtures of MgO and MgAl2O4. Moreover,strong emissions of Eu3+ ions are present in these new host materials. These results indicate that Mg-Al-Eu ternary LDH may be a potential candidate for materials applied in fluorescent devices.

The Şahin-village clay deposit, situated in the vicinity of Kütahya, western Turkey, has a promising reserve suitable for tile production. In order to evaluate its potential use, 27 clay samples were collected and their mineralogical, chemical, firing and technological properties were evaluated. The reaction of samples with dilute HCl, dispersion in water and their swelling properties were determined. Mineral identification studies were conducted using X-ray powder diffraction (XRD), differential thermal analyses (DTA) and scanning electron microscopy (SEM) techniques. Analysis showed that clay minerals are illite, kaolinite and montmorillonite. Non-clay minerals are quartz, muscovite, microcline and goethite. The clay samples consisted mainly of SiO2 and Al2O3 corresponding to about 81–83% (average) because of the presence of clay minerals and quartz, accompanied by a significant amount of iron oxide. Mineralogical, chemical, thermal analysis and technological tests showed that the clays from Şahin village could be used for stoneware tiles, tile and brick-making.

Complexes of SnCl2/montmorillonite have been prepared from solutions which contained 10, 20, 40 and 200 times the cation exchange capacity of the clay, resulting in complexes which contained 1·7, 1·6, 2·8 and 4·6 wt% of tin. Detailed thermogravimetric and variable temperature 119Sn Mössbauer spectroscopic studies of these complexes, both as prepared and following back exchange with Ca2+-ions, have shown that (i) the complexes are quite acidic in nature, and (ii) the majority of the Sn forms an oxy/hydroxy coating over the montmorillonite surface in which the vibrational freedom of Sn depends upon both the Sn content and the state of hydration of the coating.

Corrugated mats of palygorskite occurring in regolith overlying a fissured limestone were examined by X-ray diffraction, infrared spectroscopy, and electron optical techniques after heating at 50°C intervals to 700°C. Palygorskite ‘anhydride’ formed at 400°C and sillimanite formed at 500°C. The palygorskite is believed to have formed in joints in limestone of Upper Oligocene age (Duntroonian) prior to uplift and subsequent weathering. It is highly crystalline, and appears not to have altered or weathered since precipitation.

Associée à une méthode de coupes minces effectuées normalement aux feuillets, la microscopie électronique permet de visualiser les feuillets avec ses différentes couches. Mais sa résolution, limitée à 2 ou 3 Å, ne permet pas d'étude structurale véritable.

Le diagramme de diffraction électronique 001 contient théoriquement toutes les informations sur la structure suivant la normale aux feuillets. Mais étant donné l'épaisseur relativement élevée des préparations, l'effet dynamique rend l'interprétation difficile. Les auteurs ont testé la méthode sur un mica, muscovite, phyllosilicate particulièrement bien cristallisé. En utilisant comme étalons des cristallites de NaCl, de même aisseur éaisseur équivalente, ils ont pu montrer que l'approximation de la théorie dynamique à deux faisceaux éait valable. En comparant à des résultats obtenus par traitement thermique, ils ont pu mettre en évidence une rapide déshydroxylation et un départ du potassium sous l'effet du bombardement électronique dans le microscope.