Chemical and mineralogical transformations of phyllosilicates are among the most important in diagenetic environments in all types of rocks because they can exert a large control on the processes taking place in such environments and/or provide constraints for the conditions in which phyllosilicate transformation occurred. Dissolution-precipitation and solid-state transformation are usually the two mechanisms proposed for such reactions depending on the crystal-chemical and morphological similarities between parent and neoformed phases together with knowledge of the environmental conditions. These two mechanisms, however, may be at both ends of the spectrum of those operating and many transformations may take place through a mixture of the two mechanisms, generating observable elements that are characteristic of one or the other. In the present literature, the boundaries between the two mechanisms are not clear, mainly because dissolution-precipitation is sometimes defined at nearly atomic scale. It is proposed here that such small-scale processes are considered as a solid-state transformation, and that dissolution-precipitation requires dissolution of entire mineral particles and their dissolved species to pass into the bulk of the solution. Understanding the reaction mechanisms of diagenetic transformations is an important issue because they impinge on geochemical conditions and variables such as cation mobility, rock volume, fabric changes, rock permeability, stable isotope signature and phyllosilicate crystal-chemistry.

I propose that, in the lower range temperatures at which clay mineral transformations take place, energy considerations favour solid-state transformation, or reactions that involve the breaking of a limited number of bonds, over dissolution of entire grains and precipitation of crystals of the new phase. Large morphological changes are frequently invoked as evidence for a dissolution-precipitation mechanism but changes in particle shape and size may be achieved by particle rupture, particle welding or by hybrid processes in which dissolution-precipitation plays a minor role.

Past and recent studies of phyllosilicate transformations show chemical and structural intermediates indicating a large crystal-chemical versatility, greater than is commonly recognized. These intermediates include tetrahedral sheets of different composition within TOT units (termed polar layers), dioctahedral and trioctahedral domains in the same layer, and 2:1 and 1:1 domains also within the same layers. The existence of such intermediate structures suggests that the reaction mechanisms that generated them are within the realm of the solid-state transformation processes.

The influence of hydrological conditions and the pH of the environment on chlorite and mica transformations in the acidic weathering zone of pyrite-bearing schists was studied. Phyllosilicate transformations were investigated in the area of the abandoned pyrite open-pit mine in Wieściszowice (Lower Silesia, SW Poland) using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and chemical methods. (Mg, Fe)-chlorite, micas (muscovite and paragonite), quartz, feldspars and pyrite were reported to be the most abundant minerals occurring in pyrite-bearing schists. Phyllosilicate transformations were significantly stronger in dry conditions than in wet ones. This conclusion was supported by the fact that the inherited phyllosilicates predominated in the clay mineral fraction of waterlogged saprolites, whereas the secondary swelling minerals were minor components. In dry and extremely acidic saprolites (pH < 3), trioctahedral chlorite was dissolved and transformed into clay minerals (e.g. smectite and kaolinite), whereas swelling clays (smectite mainly) were formed at the expense of dioctahedral micas. The pH of water is an important factor influencing phyllosilicate transformations in waterlogged conditions. The phyllosilicate alterations under the influence of extremely acidic waters (pH < 3) were more advanced than in moderately acidic ones (pH of 4.6), as the secondary clay minerals seemed to be represented exclusively by smectite in the former, whereas HIMs and mixed-layer minerals such as R0 I-S-Ch, R0 I-S, as well as R1 Ch-V and/or R1 Ch-S occurred in the latter.

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.

Iron is the fourth most common element by mass in the Earth's crust and forms compounds in several oxidation states. Iron (hydr)oxides, some of which form inherently and exclusively in the nanometre-size range, are ubiquitous in nature and readily synthesized. These facts add up to render many Fe (hydr)oxides suitable as catalysts, and it is hardly surprising that numerous studies on the applications of Fe (hydr)oxides in catalysis have been published. Moreover, the abundant availability of a natural Fe source from rocks and soils at minimal cost makes the potential use of these as heterogeneous catalyst attractive.

Besides those Fe (hydr)oxides that are inherently nanocrystalline (ferrihydrite, Fe5HO8.4H2O, and feroxyhyte, δ’-FeOOH), magnetite (Fe3O4) is often used as a catalyst because it has a permanent magnetization and contains Fe in both the divalent and trivalent states. Hematite, goethite and lepidocrocite have also been used as catalysts in their pure forms, doped with other cations, and as composites with carbon, alumina and zeolites among others.

In this review we report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fenton-like system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure. The catalytic efficiency of Fe (hydr)oxides is strongly affected by factors such as the Fe oxidation state, surface area, isomorphic substitution of Fe by other cations, pH and temperature.

No comprehensive study has yet been conducted to determine the chronostratigraphic distribution of palygorskite in the Tertiary sediments of Iran. Thirty sediment samples of different Tertiary epochs were taken, based on the field observations and geological maps. The clay fraction of samples was then investigated by X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM), and inductively coupled plasma mass spectrometry (ICP-MS). Results showed that sediments of the Miocene and Pliocene had large amounts of palygorskite whereas no trace of this mineral was found in the sediments from the Palaeocene, Eocene and Oligocene. Geochemical analyses revealed that sediments younger than the Oligocene had greater amounts of soluble Mg and H4SiO4 and a higher pH than those of the Palaeocene and Eocene. The stability diagram of the smectite-palygorskite system suggests that smectite is unstable and transforms to palygorskite in Neogene sediments. The SEM micrographs showed palygorskite as interwoven fibrous mats, coatings, pore-fillings and pore-bridging material in Neogene sediments. This textural evidence suggests a direct chemical precipitation of palygorskite by dissolution of silicates under the alkaline conditions. The results also suggest that geochemical conditions in the Early Tertiary era, represented by deep-sea conditions in central Iran, were not apparently favourable for palygoskite formation until the Late Oligocene.

This study aims to find alternatives to some overexploited deposits in the north of Tunisia. The clays of the Sidi Khalif formation, of Uppermost Jurassic to Lower Cretaceous age, seem suitable to support this strategy, due to their abundance. In terms of mineralogy, they can be divided into two distinct groups, related to their palaeogeographic and eustatic contexts. The clays of the Sidi Khalif formation from Jebel Houareb (JH) and Jebel Meloussi (JM) are richer in clay minerals, while those of Jebel Rhouis (JR) and Jebel Boudinar (JB) zones are dolomite-rich. The compositional differences between the two groups influenced their technological behaviour in production of ceramic tiles. Upon firing, forsterite and gehlenite crystallized in the carbonate-rich JR and JB clays, whereas mullite formed in the JH and JM clays. Concerning their ceramic properties, the tiles made from JR or JB clays showed low bending strength and high water absorption. For JH and JM, the tiles had slightly greater mechanical resistance, but exhibited considerable linear shrinkage. These defects were partially corrected by introducing new formulations based on the same clays and by altering the firing cycles (HM1, HM2, RB1 and RB2). With these modifications, “Porcelanico” and “Monoporosa” technologically conforming tiles were obtained from HM2 and RB2 formulations, respectively.

A set of fine-grained samples from a turbiditic sequence in a Southern Pyrenees foreland basin (Jaca Basin, Eocene) were studied to determine the influence of tectonics (Pyrenean Orogeny) on phyllosilicate recrystallization and infer the grade and basin maturity. The samples from four different outcrops were examined by X-ray diffraction (XRD) and by scanning (SEM) and transmission electron microscopy (TEM) with special emphasis on clay-mineral characterization (e.g.illitic phases). The analysed samples have simple mineral assemblages and consist of detrital quartz, albite and calcite, scarce clay matrix (mainly illite with chlorite), and calcite and dolomite cement. The lack of other phyllosilicates such as mixed-layer illite-smectite (I-S), pyrophyllite, Na-micas, or kaolin minerals is quite remarkable. On the SEM scale, samples (with marl composition) have poorly sorted textures and high detrital contents. In many cases they show bedding and/or cleavage, and in some cases neither is observed. Most of the clay-sized illites show very similar crystallinity and b0 values (determined by XRD) and distributions of crystallite thickness (measured by TEM) in all the outcrops, which is typical of late-diagenesis illites forming under low-pressure conditions. These illites are parallel (or subparallel) to bedding or randomly orientated. They are also characterized by disordered polytypes and low K contents. In some TEM images, a second type of illite has been observed. This secondary illite occurs parallel to cleavage, with thicker crystals (25–35 layers), K contents in the interlayer, and a 2M1 polytype. The pole figure analysis shows that most of the clays have (00l) planes parallel (or subparallel) to bedding although there are abundant clays with random orientation. There is no trend in the clay orientation/disorientation from the south to the north of the basin. All the data indicate that the strain rate associated with the Pyrenean Orogeny has not been recorded in the turbidite sequence controlling the relative orientation of clays, although anchizonal clay crystallization is favoured as a minor process.

Basalts and related magmatic rocks such as diabase are frequently used as raw materials in the building and construction industry as dimension stones or as aggregates, where they may form the sub-bases of roads or railway embankments. A major characteristic controlling the quality of the raw materials is the rock strength, which can be affected by the presence of swellable clay minerals (smectites). Increasing smectite content is generally considered to increasingly affect rock integrity. Industrial practice, in which the smectite content is monitored via cation exchange capacity (CEC) methods, on the other hand, showed that both mechanically stable smectite-rich and unstable smectite-poor materials exist. We therefore studied the CEC–strength relation based on twelve samples from a German diabase quarry.

As could be expected, the sample with the highest CEC was the least stable. However, the comparison of the rock strength with the CEC of the other samples was less clear. Comparing the CEC of powders and of the 1–2 mm fraction of the same sample provided additional information. In the case of samples which are relatively stable (in spite of high CEC values), the CEC values of the powders were significantly higher than those of the 1–2 mm fraction. Samples with less rock strength, on the other hand, showed equal CEC values of the powder and the 1–2 mm fraction. This difference may be explained by different accessibilities of the smectites for CEC exchange solutions during typical experiments.

In conclusion, the application of the CEC method for quality control considering both powdered and 1–2 mm samples allows a more precise estimation of the rock strength to be made, particularly for the comparison of different materials. Although measurement of two CEC values (after both sieving and grinding) would complicate quality control, the present study indicates that valuable additional information, i.e. semi-quantitative information on the accessibility of smectites, is gained.

In this study, natural bentonite was modified with hexadecyltrimethylammonium (HDTMA) bromide to obtain organobentonite (HDTMA-bentonite). Bentonite and HDTMA-bentonite were then characterized using XRD, XRF, SEM, FT-IR, thermogravimetric (TG) analysis, elemental analysis and Brunauer-Emmett-Teller (BET) surface area techniques. The HDTMA+ cation was found to be located on the surface and enters the interlayer spaces of smectite according to the XRD and SEM results. FT-IR spectra indicated the existence of HDTMA functional groups on the bentonite surface. The BET surface area significantly decreased after the modification due to the coverage of the pores of natural bentonite. After the characterization, the adsorption of a textile dye, Reactive Blue 19 (RB19), onto bentonite and HDTMA-bentonite was investigated. The maximum adsorption capacity of HDTMA-bentonite for RB19 was 502 mg g-1 at 20°C. The adsorption process followed a pseudo-second-order kinetic model and it was exothermic and physical in nature.

Interstratified illite-smectite (I-S) occurring authigenically in diverse earth crust environments reacts toward more illite-rich phases as temperature increases. For that reason, I-S is used for geothermometry when prospecting for hydrocarbons or ore mineral deposits. This study develops the mathematical relations for characterizing the coherent stacking potential of fundamental particles (FP) using the expandability ratio K, where K is defined as (%SMAX –; %SXRD)/%SMAX. The ratio can be applied to differentiating I-S samples from shales, bentonites, and hydrothermal alterations. In particular, patterns on a K vs. T diagram, where T is the average thickness of fundamental particles (FPs), appear to be indicative of the geological conditions related to I-S formation. Shale samples plot in the negative K domain of the diagram, possibly due to the intimate mixing of detrital particles. Both bentonitic and hydrothermal samples display trends of increasing K with T, which suggests the coherent stacking potential progressively decreases as FPs increase in thickness. Hydrothermal samples are more extensively distributed on the diagram than samples from bentonites. This result may reflect differences in particle growth conditions (nutrients and space) between bentonites (short supply) and hydrothermal alterations (good supply).

The Triassic-Jurassic boundary (TJB) is marked by one of the five largest Phanerozoic mass extinctions. To constrain existing models for TJB events, we obtained a stratigraphically highly resolved dataset from a marine section at Kendlbachgraben, Austria.

The topmost Triassic Kössen Formation contains low to medium-charged smectite and vermiculite as alteration products of mafic-ultramafic minerals. The clay minerals in the boundary mudstone are kaolinite ⩾ illite + muscovite ⨠ smectite > chlorite. Predominant kaolinite suggests humid climate and abundant terrigenous input. In the lowermost Jurassic, the clay mineral pattern changes to illite + muscovite ⨠ kaolinite ⨠ smectite, which reflects change to less humid and more moderate climate.

The topmost Kössen Formation also contains clay spherules. Their composition, shape and size indicate that they are alteration products of airborne volcanic glass droplets solidified in the air, settled in the sea and altered rapidly with negligible transport in terrestrial or marine environments. Our data are consistent with sudden climatic change at the TJB, as a result of large-scale volcanic activity of the Central Atlantic Magmatic Province which produced distal airfall volcanic ash.

The use of organoclays as adsorbents in the remediation of polluted water has been the subject of many recent studies. In the present work, a Tunisian smectite modified with two cationic surfactants was used as an adsorbent to examine the adsorption kinetics, isotherms and thermodynamic parameters of fluoride ions from aqueous solution. Various pH values, initial concentrations and temperatures have been tested. Two simplified kinetic models, first-order and pseudo-second-order, were used to predict the adsorption rate constants. It was found that the adsorption kinetics of fluoride onto modified smectites at different operating conditions can best be described by the pseudo-second-order model. Adsorption isotherms and equilibrium adsorption capacities were determined by the fitting of the experimental data to well known isotherm models including those of Langmuir and Freundlich. The results showed that the Langmuir model appears to fit the adsorption better than the Freundlich adsorption model for the adsorption of fluoride ions onto modified smectites. The equilibrium constants were used to calculate thermodynamic parameters, such as the change of free energy, enthalpy and entropy. Results of this study demonstrated the effectiveness and feasibility of organoclays for the removal of fluoride ions from aqueous solution.

In Argentina, the only halloysite deposits found so far are located in the southwest of the province of Rio Negro. The areas are named Mamil Choique and Buitrera, separated by 50 km in a W–E direction. The deposits are located in pyroclastic rocks, rhyolitic tuffs and ignimbrites.

The aim of this paper is to determine the origin of the alteration, any relationship between the processes in Mamil Choique and Buitrera, and the factors which controlled the halloysite formation. The work was based on field work, mineralogical and geochemical studies, form and distribution of the alteration. Fresh as well as altered rocks were collected. The first were studied by petrographic and chemical methods. In altered samples, the clay mineralogy was determined by XRD and textures by SEM and TEM. Chemical analyses on fresh and altered samples were used to characterize the alteration process and the rock composition.

It was concluded that halloysite has been formed by weathering in a time range from Middle Eocene to Middle Oligocene and extended along 50 km in a W-E direction, independent of the source rock. Particle morphology depends on the original texture of the rock. Spheroidal halloysite is related to rocks with low porosity and tubular particles are related to rocks with open spaces.

To provide fundamental knowledge for studying the relative content of vacant sites and exploring the mechanism of interaction between Pb2+ and birnessite, Fourier transform infrared spectroscopy (FTIR) of birnessites with different Mn average oxidation states (AOS) before and after Pb2+ adsorption were investigated. The number of absorption bands of FTIR spectra was determined by using the second derivatives of the original spectra. The band at 899–920 cm–1 was assigned to the bending vibration of -OH located at vacancies. The bands at 1059–1070, 1115–1124 and 1165–1171 cm–1 could be attributed to the vibrations of Mn(III)-OH in MnO6 layers, and the intensities of these bands increased with decreasing Mn AOS. The bands at 990 and 1023–1027 cm–1 were ascribed to the vibrations of Mn(III)-OH in the interlayers. Mn(III) in MnO6 layers partially migrated to interlayers during Pb2+ adsorption, which led to an increased intensity of the band at 990 cm–1. The band at 564–567cm–1 was assigned to the vibration of Mn-O located at vacancies. This band could split by coupling of vibrations due to Pb2+ and/or Mn2+ adsorbed at vacant sites. The large distance between the band at 610–626 cm–1 and that at 638–659 cm–1 might reflect small Mn(III) ions located in Mn(III)-rich rows.

The empirical application of muds for therapeutic purposes is widely known. This is called pelotherapy and consists of the local or generalized application of a mixture of a solid phase and a liquid phase (peloid) for the recovery of arthro-rheumatic issues, bone-muscle traumatic damage and dermatological pathologies. During the time of mixing (maturation process) the mud is progressively colonized by thermophilic microorganisms that contribute to improvements in the peloid quality and endow the mud with organic substances. Several studies report diatoms as the main agent of thermal muds capable of producing anti-inflammatory sulphoglycolipid which renders the mud suitable for this use. The effect of the temperature is also considered important for therapeutic purposes.

Recent studies assessed physical, chemical and technological properties of some peloids in use at spa centres. Some maturation surveys have also been performed in recent years. The need for quality criteria establishment and certification of clayey products intended to be used currently is evident, especially for peloids which have therapeutic action. Consequently, this study aims at the compilation and analysis of some characteristics of peloids from the literature in order to contribute to a major database that allows the establishment of regulations and quality criteria for suitable applications of peloids.

Early Cretaceous glauconite from the Xiala section, southwestern Tibet, China, was investigated by petrographic microscopy and scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, and electron probe microanalysis (EPMA). The investigations revealed that the glauconite in both sandstones and limestone is highly evolved. The glauconite in sandstone is autochthonous, but in limestone it may be derived from the underlying glauconitic sandstone. Based on analyses of the depositional environments and comparisons of glauconite-bearing strata in Zanda with sequences in adjacent areas, we conclude that the glauconitization at Zanda was probably associated with rising sea levels during the Late Albian, which represent the final separation of the Indian continent from the Australian-Antarctic continent. After the separation of the Indian continent from the Australian-Antarctic continent, cooling of the Indian continent resulted in subsidence and northward subduction of the Indian plate. A gradually rising sea level in Zanda, located along the northern margin of the Indian continent, was the cause of the low sedimentation rate. Continued transgression resulted in the occurrence of the highly evolved glauconite in this area.

The exchange reaction of Na-bentonite with zirconium pillars gives products which suffer from a loss of crystallinity, with basal spacing about 18 Å and surface area of 200 m2 g–1. Aluminium introduced in different amounts in the zirconium intercalated solution leads to an improvement in the stability and crystallinity of zirconia-pillared clays (Zr-PILCs) and creates pillared clays with new properties. Adding a small amount of Al (10 molar %) leads to an increase of d001 from 18 Å to 20.5 Å and an increase of the percentage of introduced zirconium from 16.71 to 21, expressed as ZrO2 wt.%, accompanied by an increase of the Brönsted and Lewis acidic sites. The acetalization of acetone with ethylene glycol was studied in order to compare the activity of PILCs. The results show that the yield of the aforementioned reaction depends strongly of the composition and acidity of the catalyst.

The potential of platy nanofillers like clays in polymer nanocomposites is mostly determined by their aspect ratio. The degree of improvement that may be achieved in respect to reinforcement, gas-barrier properties and flame retardancy critically depends on the aspect ratio. Thus, increasing the aspect ratio is highly desirable in order to explore the full potential of the clay filler. Mechanical shear stress as generated in the grinding chamber of a stirred media mill (ball mill) induced an efficient exfoliation of highly hydrated and therefore ‘shear-labile’ synthetic Mg-fluorohectorite in aqueous dispersion. The attainable degree of exfoliation can be tuned and controlled through the shear forces applied by changing process parameters such as solid content and grinding media diameter. Characterization and evaluation of the exfoliation efficiency during milling was achieved by combining and cross-validating data obtained by powder X-ray diffraction (XRD), static light scattering (SLS), specific surface area measurements applying the Brunauer-Emmett-Teller (BET) equation, and scanning electron microscopy (SEM). This led to the identification of optimal processing parameters, allowing for control of the degree of exfoliation and, consequently, the aspect ratio of the nanoplatelets. Not surprisingly, besides exfoliation, increasing the magnitude of the shear stress also resulted in some reduction in platelet size.

The clay platelets obtained showed a high average aspect ratio (>600), several times greater than that of original synthetic fluorohectorite. The increase of aspect ratio was reflected in a significant enhancement of both specific surface area and cation exchange capacity (CEC) of the external basal surfaces. This method has substantial advantages compared to microfluidizer processing with respect to feasibility, batch size and particle diameter size preservation. The exfoliated nanoplatelets obtained by milling have great potential to improve mechanical properties of polymer layered silicate nanocomposites (PLSN).

The aim of this research was to assess the potential application of the Late Cretaceous levels as raw material for the production of ceramic tiles. Mineralogical, chemical and grain size distribution studies were carried out on four clays sampled at different sites in the Tunisian Central Atlas. Clays are mainly composed of phyllosilicates, usually illite and kaolinite. Quartz, feldspars and dolomite were also detected.

Tiles were prepared by pressing clay bodies at 250 bar and then firing at different temperatures following industrial conditions as closely as possible. Thermal analysis showed the influence of mineralogical composition and grain size distribution on the material behaviour during firing. The physical properties of fired tiles were obtained from specific tests in accordance with international standards (ISO), i.e. the firing shrinkage, water absorption, apparent density and flexural strength. The development of physical properties indicates an optimal firing range between 1050–1150°C. Results demonstrate the potential of Late Cretaceous materials as raw materials for the production of ceramic tiles.

Clay minerals find a wide range of application in composites, paints, drilling liquids, cosmetics, and medicine. This article reviews chemical and physical properties of natural and organically modified clay minerals to understand the nanometre-scale structure, surface characteristics, and application in functional materials. The relation between fundamental properties and materials design is emphasized and illustrated by examples. The discussion comprises the following: an overview; surface structure and cation density; solubility and solubility reversal by surface modification; the degree of covalent and ionic bonding represented by atomic charges; the distribution of metal substitution sites; measurements and simulations of interfacial properties at the nanometre scale; self-assembly, packing density, and orientation of alkylammonium surfactants on the clay mineral surface; the density and chain conformation of surfactants in organic interlayer spaces; the free energy of exfoliation in polymer matrices and modifications by tuning the cleavage energy; thermal transitions, diffusion, and optical responses of surfactants on the mineral surface; elastic moduli and bending stability of clay layers; and the adsorption mechanism of peptides onto clay mineral surfaces in aqueous solution. Potential applications in biotechnology and other future uses are described.