Soil clay minerals in recent natural polders react on a human timescale in response to local environmental conditions. With increasing age, the mineral reaction leads to the dissolution of the chlorite component and a composition change of the different illite-smectite mixed-layer minerals (I-S MLMs): i.e. smectite layer content decreases and illite content increases. The process of oxidation, which is proven by magnetic susceptibility to trigger clay mineral reaction, changes the mineralogical composition of the sediment above the redox front. The mineral changes appear to be a non-linear function of time. In natural conditions the process lasts >1000 y. However, anthropoic forcing such as artificial drainage accelerates the oxidation reaction to complete the whole process in a few tens of years.

Magnetite is a redox active Fe oxide common in most soil and sedimentary environments. In this study, we investigated magnetite transformations under extreme alkaline conditions (0.1–2 mol l–1 NaOH) similar to those found under high-level radioactive waste storage tanks at the Hanford site in the State of Washington, USA. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that magnetite was transformed into maghemite and goethite, and the XRD peak intensities for goethite increased with NaOH concentration. Goethite was presumably formed through reconstructive dissolution/crystallization reactions that can be written as: Fe3O4 + OH– + H2O = γ-Fe2O3 + Fe(OH)3–; 2Fe(OH)3– + 1/2O2 + 2H+ = 2α-FeOOH + 3H2O. Some of the newly formed maghemite may also redissolve to form goethite at greater NaOH concentrations.

A scanning and transmission electron microscopy study has been performed on Oligocene glacio-marine sediments, Devonian sandstones, and Jurassic dolerites recovered during CRP-3 drilling in the Ross Sea (Antarctica). Newly formed clay minerals occur in the rock matrices and as fillings in veins and faults which crosscut the whole sequence. Authigenic clays in sediments consist of beidellite-montmorillonite, berthierine/chlorite intergrowths and illite. Al,K-rich smectites and kaolinite occur in the Devonian sandstones. Saponite, berthierine/chlorite intergrowths, and Fe-hydroxides develop in the altered dolerites. Hence, the composition of the secondary phases depends also on the geochemistry of the rock they grow in. Within each sample, the same authigenic minerals form in the matrix and in the vein/fault. Clays precipitated from fluids, with variable fO2 values, which circulated in the system during the contemporaneous diagenetic and faulting events.

The mineralogical characteristics of authigenic palygorskite occurring with chlorite and illite in Miocene sediments in Linxia basin were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The XRD results suggest that the mineral composition of the sediments includes mainly quartz, chlorite, illite, calcite, plagioclase, orthoclase, minor palygorskite and small amounts of gypsum and ankerite. Two kinds of palygorskite were observed in the sediments, relatively straight fibrous particles found in matted, felted masses associated with platy chlorite and silky aggregates found in the void spaces. The former probably replaces chlorite grains, growing from the edges or the fissures of chlorite particles. Chlorite grains exhibit bay-shaped or rounded edges, with ambiguous felted boundaries between chlorite particles, indicative of an intensive dissolution process and the growth of palygorskite at the expense of chlorite. Palygorskite is also observed as inclusions within calcite, sprouting from or coating calcite surfaces, suggesting that palygorskite crystallized from solution. The textural relations of palygorskite and the occurrence of ankerite and the characteristically Fe-bearing palygorskite in the sediments suggest the destruction and hydrolysis of chlorite. The ankerite seems to be preferentially present in the void spaces, closely associated with chlorite and illite; fibrous palygorskite crystallizes at the edges of these clay mineral particles and the platy clay mineral particles are gradually replaced by fibrous palygorskite crystals, suggesting that alteration of chlorite to palygorskite involves an interaction with water during the diagenetic process.

In liquid-filled batteries, the liquid electrolytes may escape or present a fire hazard and an inert spacer is needed to separate the electrodes. Alternative polymer-based electrolytes are of current technological interest. Solid polymer electrolytes are non-volatile, non-corrosive materials, which can readily be processed into any shape or size. However, despite possessing the required mechanical properties, they have inherently lower conductivity. Gel-based systems are an attempt to strike a balance between the high conductivity of organic liquid electrolytes and the dimensional stability of a solid polymer.

Rectorite was modified with dodecyl benzyl dimethyl ammonium chloride to form organic-modified rectorite (OREC). OREC was used as a filler additive to modify gel polymer electrolytes (GPEs) and prepare composite gel polymer electrolytes (CPEs) which consisted of polymethyl methacrylate (PMMA) used as a polymer matrix, propylene carbonate (PC), used as a plasticizer, and LiClO4, used as a lithium ion producer. A variety of physical and chemical techniques was used to characterize the CPEs. The interlayer d spacing of OREC was much larger than that of the initial rectorite (2.22 nm). OREC also possesses a fine microscopic structure, and has a hydrophobic surface. Molau and XRD analysis of CPEs indicate that OREC has good compatibility with the components of CPEs and can be dispersed well. The effects of temperature and OREC dose on properties were studied. The temperature dependence of ionic conductivity of CPEs is well fitted by the VTF (Vogel-Tamman-Fulcher) relation. OREC doses of 5 phr gave the greatest ionic conductivity. This amount also greatly increased the plasticizer maintenance levels. Due to the occupancy of free volume space in the polymer matrix of CPEs by OREC, the bulk resistance of the CPEs was lowered and the glass transition temperature (Tg) increased. The sheet structure of OREC is thought to improve the decomposition temperature of CPEs.

The Capim Kaolin District (eastern Brazilian Amazon), is one of the largest kaolin deposits in the world; with the kaolin used mainly for paper coating. The kaolin developed at the expense of Cretaceous sandy-clayey sediments of the Ipixuna formation, through intense lateritization from the Mesozoic to Cenozoic times.

This work describes the morphological, mineralogical, crystallochemical and geochemical evolution of the Capim kaolin facies. Based on the profile analysis in the open pit fronts, it encompasses X-ray diffraction, thin-section optical analysis, EDS-assisted scanning electron microscopy and transmission electron microscopy, chemical analysis, infrared and Mössbauer spectroscopies.

Six facies were defined as different stages of the supergene process. Ferruginization led to a thick duricrust on the soft kaolin, which in turn evolved from sandy-clayey sediments of the Ipixuna Formation. A subsequent deferruginization event degraded the duricrust, resulting in the flint kaolin facies.

This study is located on the bentonite outcrop of ‘El Toril’ (Cabo de Gata, Almeria, Spain), where acid solutions have resulted in an alteration front that has caused physical, chemical and mineralogical changes in the bentonite material. The main objective is to assess these changes and to draw a model of evolution of this front in the outcrop. The most important chemical and mineralogical changes observed consist mainly of the loss of mass in the bentonite, the formation of kaolinite, the precipitation of jarosite and alunite from leachates and important changes in the rare earth element distribution pattern. No sulphurs have been identified in the pyroclastic rock at the top of the outcrop, but the presence of dissolution marks and the high concentrations of As, Pb and V in the rock overlying the bentonite point towards the existence, in principle, of these sulphurs and suggest that meteoric alteration is mainly responsible for the genesis of the outcrop.

We have carried out optical microscopy, X-ray diffraction (XRD) and scanning and transmission electron microscopy (SEM and TEM) studies of phyllosilicates from black slates of very low to low-grade metamorphism. Such slates belong to a Middle/Late Devonian basin and an Early Carboniferous basin associated with the Porto–Tomar–Ferreira do Alentejo strike-slip shear zone (Ossa-Morena Zone, Portuguese Iberian Variscan Massif). These black slates are imbricated in an Upper Proterozoic substratum of higher metamorphic grade. Kübler Index values of white micas and mineral assemblages deduced from the XRD, SEM and TEM data (muscovite, chlorite and pyrophyllite) indicate high anchizonal and epizonal metamorphic conditions for slates from these basins. The b parameter and the phengitic contents of mica suggest the occurrence of low pressures (1–2 kbar) related to an extensional geotectonic setting. The dense fracture network shown by SEM images and the high density of crystal defects revealed by the TEM study in the eastern basin, adjacent to faults produced by shearing, suggest that their epizonal phyllosilicates were more affected during deformation than those belonging to the western basin, favouring the development of a retrograde association (siderite, kaolin group minerals and Al-smectite) on the epizonal paragenesis. Microcavities formed along phyllosilicate cleavage acted as channels for fluid transport favouring alteration under low-temperature conditions.

Numerous studies focus on the relationships between chemical composition and OH-band positions in the infrared (IR) spectra of micaceous minerals. These studies are based on the coexistence, in dioctahedral micas or smectites, of several cationic pairs around the hydroxyl group which each produce a characteristic band in the IR spectrum. The aim of this work is to obtain the wavenumber values of the IR OH vibration bands of the (Al-Fe3+)-OH and (Fe3+-Fe3+)-OH local cationic environments of ‘pyrophyllite type’ in order to prove, disprove or modify a model of dioctahedral phyllosilicate OH-stretching band decomposition. Natural samples are characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies and electron microprobe; the hydrothermal synthesis products are also analysed by powder XRD and FTIR after inductively coupled plasma measurements to obtain the chemical compositions of starting gel phases. Natural samples contain some impurities which were eliminated after acid treatment; nevertheless, a small Fe content is found in the pyrophyllite structure. The amount of Fe which is incorporated within the pyrophyllite structure is much more important for the synthetic samples than for the natural ones. The IR OH bands were clearly observed in both natural and synthetic pyrophyllites and assigned to hydroxides bonded to (Al-Al), (Al-Fe) and (Fe-Fe) cationic pairs. During this study, three samples were analysed by DTG to check the cis- or trans-vacant character of the layers and to determine the influence of this structural character on the OH-stretching band position in IR spectroscopy.