SWy-2 (Wyoming), Sap-Ca saponite (California) and SAz-1 (Cheto, Arizona) were exchanged with different cations (Al, Ni, Mg, Ca and Na). The catalytic activity of these ionexchanged clays was measured directly using the isomerization of α-pinene at 80°C for 2 h to yield camphene, limonene and other minor products. The order of activity for the different cationexchanged forms was Al > Ni > Mg > Ca > Na, which correlated well with the known polarizing power of these cations and the resulting interlayer acidity. Catalysts derived from Sap-Ca were the most active followed by SWy-2, with SAz-1 the least active by a considerable margin. The greater activity of Sap-Ca over SWy-2 was attributed to the high tetrahedral charge in the former. Reduction of the layer charge of SAz-1 using Li fixation caused a significant improvement in the catalytic activity of the Al-exchanged reduced-charge SAz-1.

In this paper, the role of Cu in the adsorption of the cationic pesticide chlormequat (CCC) on montmorillonite is studied. The adsorption of CCC was measured in various media, e.g. water and aqueous solutions of NaCl, CaCl2 and Ca(NO3)2 at the same ionic strength (I= 0.01 mol l–1). The retention of CCC on montmorillonite in aqueous media is due principally to a cationic exchange process with inorganic cations which saturate the interlamellar positions on this mineral. However, the amount of inorganic cations liberated from montmorillonite was ∼15% less than the amount of CCC adsorbed. This indicates that not all the pesticide was adsorbed through cation exchange.

The adsorption of CCC in aqueous media decreased in the presence of a heavy metal, compared with metal-free treatment. This behaviour indicates competition between the two cations for interlamellar positions. The adsorption of CCC in the presence of Cu also decreased in electrolyte media with the effect being highest in the presence of Ca electrolytes. The maximum CCC diminution was ∼30%. However, the isotherms derived in CaCl2 and Ca(NO3)2 media at different Cu concentrations were close to each other, indicating that Ca from background electrolyte exerts greater competition than Cu for montmorillonite planar positions.

The physicochemical properties of clays can be modified by acid treatment with inorganic acids. This treatment is usually referred to as ‘acid activation’, because it increases the specific surface area and the number of active sites of the solids. In the present study, the acid activation of saponite from Cerro del Aguila (Madrid, Spain) with HCl solutions was measured. Illite, quartz and small amounts of feldspar were found as impurities in the raw saponite.

Acid treatments were carried out with different concentrations of HCl solutions. The samples obtained were characterized by mineralogical and chemical analyses, XRD, FT-IR spectroscopy, N2 adsorption-desorption isotherms and TEM. The acid attack, under the conditions employed, produced a progressive destruction of the structure of saponite by partial dissolution of the octahedral Mg(II) cations. Amorphous silica coming from the tetrahedral sheet of saponite was generated. The specific surface area of the most intensely treated sample (2.5% for 24 h) was doubled with respect to that of natural saponite. This increase in the surface area is due to the increase in both the external and internal surface areas.

Experimental alteration of a rhyolitic obsidian by solutions containing variable concentrations of Mg was carried out at 100, 150 and 200°C, for 30, 60 and 90 days, to investigate the mechanism of smectite formation. The smectite exhibits two distinct morphologies: (1) small flakes (aggregates of a few crystals); and (2) large flakes (massive groups). The small flakes are the earlier alteration products. Both morphological types have distinct chemical compositions: the smallest laminae are dioctahedral and contain more Fe, whereas the particles from the rose-shaped aggregates contain Mg and are trioctahedral. Intermediate compositions have been observed between the extreme compositions.

It is suggested that the two morphologies are the result of two distinct genetic processes: (1) the small flakes (Fe-rich smectite) form by solid state rearrangements of the hydrated external layer of glass and/or via the formation of domains within the glass; (2) the rose-shaped aggregates (Mg-rich smectite) form by precipitation from solution.

Clay mineral quantification by XRD is difficult when mixed-layer clay minerals and discrete clay types are both present. New procedures for peak decomposition and pattern simulation offer increased opportunities to obtain mineral abundance estimates. This proposed methodological sequence, for quantitative representation (QR) of complex clay samples, involves: (1) determination of layer type, mixed-layer proportion and order (R); (2) simulation of XRD patterns using MULCALC, an adaptation of NEWMOD; and (3) interpretation of the clay assemblage by fitting the whole pattern with CLAY++, a statistical program. The product is a QR of individual phases or a summation of layer types. The absence of quantitative reference standards means results cannot be checked for accuracy, but the statistical fit is highly reproducible and less prone to operator error. The QRs may be obtained with simulated or actual reference mineral patterns in the database. Results for freshwater marsh samples illustrate the approach.

The K/Ar characteristics of 53 clay assemblages (Triassic–Cretaceous), representing the detrital, volcanogenic and arid-facies clay mineral associations, are interpreted in relation to their mineralogy, chronostratic age and geological origins. The K-bearing mineral components of the 1–2 μm, 0.2–1 μm and <0.2 μm fractions of each clay assemblage together display one of two characteristic patterns of K2O and 40Ar values (the K/Ar signature of the assemblage) on a 40Ar/K2O correlation diagram. Interpretation of the K/Ar signatures indicates that: (1) all of these clay assemblages are apparently unaffected by burial diagenetic illitization; (2) the Jurassic and Cretaceous detrital clay assemblages are derived from the reworking of weathered Caledonian metasediments (420 500 Ma) and weathered kaolin-bearing sediments of Upper Devonian/ Carboniferous age; and (3) the role played by palaeoclimate in developing the pattern of clay minerals in the Mesozoic sediments of England is much less significant than previously believed.

Ethyl cinnamate/montmorillonite intercalation complexes were obtained by gaseous adsorption of the drug on the clay surface. They were characterized by powder X-ray diffraction, differential thermal and thermogravimetric analyses and by visible-UV and IR spectroscopies. It was found that after 1 day of adsorption, most of the drug enters the interlayer space of the clay by substitution of water molecules, and is removed only after heating at high temperature. In addition, a portion is physisorbed on the external surface of the crystallites, being removed easily below 100°C. The interlayer complex improves the protecting ability of the pure clay or the pure drug against ultraviolet radiation, specially in the so-called ‘C’ range (290–190 nm).

The clay fraction of the deposits of the Otjomongwa Pan, southwestern Kalahari, is dominated by Mg-smectite. This mineral formed as an authigenic precipitate in a groundwater-fed lake, without involving the transformation of a precursor mineral. During the earliest recorded period, Mg-smectite formed together with sepiolite and dolomite in a shallow lake. This period was ended by a change in environmental conditions that led to an increase in the depth of the lake and a decrease in salinity and Mg content of the water. This resulted in a transition to a mineral association without sepiolite and including calcite, together with Mg-smectite and dolomite. The depth of the lake gradually decreased after this event, while the lake water progressively became depleted in Mg.

The use of solid-laden emulsions (Pickering emulsions) provides an interesting alternative to normal emulsions because the need for organic surfactants is removed or reduced. Combination of a bentonite with a layered double hydroxide represents an effective emulsifying system and provides high stability against coalescence. Solid contents as low as 0.1% (w/w, related to the total mass of the emulsion) are sufficient to prepare very stable O/W emulsions; the mass ratio of hydroxide/bentonite is not critical but should vary between 0.25 and 4 (corresponding to mass fractions of the hydroxide between χ = 0.2 and 0.8). With large hydroxide contents, stabilization is mainly caused by the envelope of hydroxide particles around the oil droplets. This shell provides a mechanical barrier against coalescence, typical of Pickering emulsions described so far. Addition of increasing amounts of bentonite provides an additional stabilization by building-up a threedimensional network consisting of both types of particles spanning the coherent phase. A high storage modulus at mass fractions of the hydroxide between 0.2 and 0.8 indicates high flexibility for the inorganic framework which is considered to be an important factor in the high stability of these emulsions.

Smectites from the E horizon of podzols dated at 1200–10,000 y in central and northern Finland were studied. Clay minerals in the fine (<0.1 μm) and coarse (0.1–2 μm) fractions were examined by X-ray diffraction. The distribution (octahedral or tetrahedral) and magnitude of the layer charge of expandable minerals were estimated using intercalation of alkylammonium ions (nC = 12) associated with the Hofmann & Klemen effect. In addition, charge alteration following desaturation (H+ exchange) and autotransformation was investigated. Smectites from the E horizons of podzols are not homogeneous but constitute a mixture of several populations with various layer charges. Smectites with lower layer charge are present in podzols having a longer effective time of pedogenesis, suggesting alteration of the high-charge smectites with time. Experimental alteration of the smectites by autotransformation shows that a decrease of the layer charge is easily produced by desaturation of the smectite clays.

Quartz-hematite veins in the St. Austell pluton feature an assemblage of authigenic kaolin, illite, chlorite and hematite. Similar assemblages occur in altered granites adjacent to the veins. Complex textures in the veins and altered granites show that kaolin was an initial precipitate from hydrothermal fluids that was subsequently replaced by illite, hematite and chlorite. The sequence of mineral precipitation reflects a kinetic control on crystal growth, with early nonequilibrium precipitation of kaolin from fluids with compositions appropriate for the equilibrium formation of illite. Hematite formed under relatively oxidizing conditions that subsequently became more reducing to permit the late precipitation of chlorite. Illite associated with the quartz-hematite veins differs texturally, mineralogically and chemically from the coarsely crystalline hydrothermal muscovite (sericite or gilbertite) associated with quartz-tourmaline veins and greisen. Quartzhematite veins are thus considered to record a distinct mineralization event that is not related to the early greisenization or the economic kaolinization.

Studies of the subsurface microbiology of the Äspö Hard Rock Laboratory, Sweden have revealed the presence of many different bacteria in the deep groundwaters which appear to maintain reducing conditions. Experiments were conducted to study the rock-water and microbial interactions. These used crushed Äspö diorite, Äspö groundwater and iron- and sulphate-reducing bacteria in flowing systems under anaerobic conditions. In column experiments, there was evidence of loss and mobilization of fine-grained crushed material (<5 μm) which had originally adhered to grain surfaces in the starting material. The mobilized fines were trapped between grains. The degree of mineralogical alteration was greater in the experiments when bacteria were present. In both column and continuously stirred reactor experiments, there is evidence for the formation of a secondary clay. These experiments have shown that microbial activity can influence rock-water interactions even in nutrient-poor conditions.

The clay mineralogy of a set of Tertiary marine sediments from the Internal Subbetic of the Betic External Zone was examined. Two types of sedimentary environment were distinguished: a platform environment consisting of limestones, marls, organogenic limestones, conglomerates and silexites distributed heterogeneously in time and space; and deep environments, where the sedimentation consisted of marls, marly limestones, marly clays and silexites, with no sedimentary gap. A third group of sediments studied belongs to the Águila Complex, with mineralogical and stratigraphic characteristics very similar to the platform sediments. This third type of sediment is found in the sediments of the Campo de Gibraltar Complex as large, disperse blocks resulting from tectonic activity. A very similar mineral association was observed in all three domains, consisting of smectite, illite, mixed-layer I-S, kaolinite and lesser amounts of palygorskite and chlorite. Materials mainly derive from the erosion of Mesozoic sediments, and sedimentation was controlled by the compressive tectonics of the region.