The relative growth rates of the three joint chains of silica tetrahedra and metal octahedra in the [100], [1̅10] and [1̅1̅0] directions within the mica layer (referring to the 1M unit-cell) seem to control the morphology of mica crystallites. Laths and fibers are the products of relatively fast growth along the [100] direction compared to growth along the [1̅10] and [1̅1̅0] directions. The (010) growth front in 1M micas with trans-octahedral vacancies exposes a pair of reactive OH ions that can form organic or inorganic complexes and ‘poison’ the growth on the (010) face.

Authigenic illite fibers in two sandstones with contrasting lithologies are found to have grown on mica or kaolinite cores. Illite fibers appear in single sets or in multiple sets, 120° apart. This texture seems to be related to the stacking sequence of the layers in mica or kaolinite in the core of these fibers.

Coarse-grained vermiculite from a serpentinite-pegmatite thermal zone displays a rational series of narrow 14.4 Å basal reflections and an unusual broad 28 Å peak. X-ray diffraction simulations and fitting techniques show that the 28 Å peak is related to 28 Å domains consisting of elongated 2:1 layers of different lengths. The domains are located at the crystal edges of the vermiculite.

The low-temperature alteration of a rhyolitic rock from Kimolos Island, Aegean, Greece, yielded an alteration profile characterized by gradual transition from fresh glass to bentonite containing homogeneous Chambers-type montmorillonite and then to a mordenite-bearing bentonite. Both mordenite and smectite were formed from poorly crystalline precursors, which probably had compositions comparable to that of the crystalline end-product. However, their composition may have been modified to some degree after reaction with the fluid phase. Particle length and width measurements of smectite crystals yielded lognormal profiles, which suggest supply-controlled crystal growth in an open system or random ripening in a closed system. The former mechanism is in accordance with the observed sustained supply of Mg and Fe by the fluid phase throughout the alteration profile and is believed to be the dominant formation mechanism of smectites in bentonites in general. In the mordenite-bearing zone, random ripening is expected in domains with low permeability, in which the system was essentially closed, favoring the formation of mordenite. The level of supersaturation with respect to smectite was probably lower in the mordenite-bearing zone. Smectite probably affected pore-fluid chemistry either through ion exchange or via dissolution of initially formed K-bearing smectite. The latter process raised the K+/(Na+ + Ca2+) activity ratio of the pore-fluid favoring K-bearing mordenite.

Nordstrandite from Lages represents the first occurrence of this mineral in an oxisoil that does not involve the influence of a calcareous substrate. This is also the first reported occurrence in Brazil. Nordstrandite occurs near the city of Lages only in the weathered bedrock facies, mostly where the circulation of meteoric water is restricted. There is also a close association between nordstrandite and the weathering of modified pseudoleucite structures. The interaction of meteoric water and feldspathic alkaline country rock with uncommon texture and mineralogy (rich in nepheline, sodalite, nosean, analcime and natrolite) promotes the development of solutions enriched in alkaline ions with basic pH, necessary to form nordstrandite. A detailed study by X-ray diffraction (XRD) and infrared (IR) spectroscopy in natural or chemically leached samples was performed to identify the Al(OH)3 polymorphs of gibbsite and nordstrandite.

The extraction of salts by layered (bentonite) and fibrous (sepiolite) clay poultices from stone materials currently used in Heritage buildings was studied. Analyses were performed on stones affected by salts but not submitted to humidity, and also on stones affected by salts and simultaneously submitted to continuous or intermittent humidity during the salt-extraction process. From the experimental results and the statistical analysis, the application of two successive poultices is sufficient for an efficient extraction of Cl− and NO3- in the absence of humidity. However, under humid conditions, the efficiency of the method is reduced considerably. For SO42-, the use of hydrotalcites (anionic clays) is recommended for more effective extraction.

The matrix of the Pliocene volcaniclastics from the Akrotiri area of the Santorini island (Greece) is dominated by clinoptilolite. Smectite, occasionally illite-smectite, opal-CT, cristobalite and mordenite are also present. The clinoptilolite-rich samples were heated at 460 and 560°C for 12 h and the reductions in the intensity of the 020 diffraction peak were measured. Electron microprobe analysis (EMPA) was then used to study the chemical composition of the clinoptilolite. Statistical analysis proved a strong and quantifiable relationship between the reduction of the 020 diffraction peak of the clinoptilolite and the Na/K ratio. A representative set of microprobe analyses of clinoptilolite was performed before any correlation with thermal behavior was attempted. The presence of K in the structure of clinoptilolite as well as its relationship with Na are most important in the thermal behavior of clinoptilolite.

The objective of this work was to prepare series of reduced-charge materials from different parent Li-saturated dioctahedral smectites, to investigate the effects of temperature, chemical composition and charge location in smectites on the charge reduction and to characterize reduced-charge smectites (RCSs) using methylene blue (MB) adsorption. The layer charge decrease, induced by Li fixation, is correlated with the trends in the spectra of MB-RCS dispersions in the visible region (VIS) spectra. Distribution of the negative surface charge of the clay minerals controls the distance between the adsorbed MB cations and thus affects the formation of MB dimers and higher agglomerates. Because each form of MB (monomer, dimer, higher agglomerate, J-aggregates) absorbs light at a different wavelength, the VIS spectra of MB depend sensitively on the charge density at the clay surface. Both cation exchange capacity (CEC) values and spectra of MB-clay dispersions clearly detect extensive reduction of the layer-charge density in reduced-charge montmorillonites (RCMs) upon Li-thermal treatment. The extent of charge reduction depends on the temperature of the thermal treatment, as well as on the octahedral charge of the montmorillonite. Reduction of the layer charge proceeds to a much lesser extent for smectites with mainly tetrahedral charge and high Fe content (Fe-rich beidellite and ferruginous smectite). Both CEC data and MB spectra detect only a slight decrease of the layer charge density, which relates to the low octahedral charge of these minerals. Following heating at higher temperatures (120-160°C), slightly higher Li fixation is indicated by CEC values; however, no charge reduction is confirmed by MB spectra. Release of protons accompanying Li+ fixation in Fe-rich smectites heated at 180 or 200°C was detected in the spectra of MB-clay dispersions and confirmed by potentiometric titrations.

Molecular dynamics computer simulations were used to study methanol molecules confined between the layers of 2:1 phyllosilicates. The model systems are based on natural Ca- and Na-rich montmorillonites. Data from the literature and determined by fitting the calculated layer spacing to experimental values were employed to obtain interactions between the charged 2:1 layers and the solvent molecules. The montmorillonite surface atoms were held rigid and the methyl group in the methanol molecule was represented by a soft Lennard-Jones sphere. Electrostatic interactions were determined by the Ewald sum method, whereas the van der Waals interactions were described by a Lennard-Jones potential. Comparison of our results with diffraction data indicates a good reproduction of the layer spacing. After the initial solvent layer forms, additional solvent layers form only after previous layers are complete. Each Ca2+ and Na+ ion in the monolayer has four and two methanol molecules, respectively, in the first solvation shell, whereas the solvation shell in the multilayer contains six and four methanol molecules, respectively. This agrees well with experimental data.

Three ball clays (SP from England, TSMA from France and UK from the Ukraine) were characterized for their dry and wet colloidal properties. On the basis of X-ray diffraction and chemical analyses the clays were classified as kaolinite-rich clay, smectitic kaolinite-rich clay and illitic kaolinite-rich clay. The ζ (zeta) potential at the clay-water interface as a function of pH, in three different electrolytes, was investigated using an electroacoustic technique. Starting from measurements of dynamic mobility, the calculated ζ potential was found to be almost constant as a function of pH for the TSMA and UK clays, while it increased from −20 to −60 for the SP clay, when potassium nitrate was used as an electrolyte. The behavior of the three clays in calcium and magnesium nitrate was slightly different: SP showed a smaller increase in ζ potential, while a small deviation from the constant behavior of the UK clay was found. The results are explained in terms of the surrounding-ion atmosphere in light of the chemical-physical properties measured. Our results may well be of use to those involved in ceramic processing.

Competitive adsorption between glyphosate and phosphate on goethite was evaluated. The influence of background electrolyte on the adsorption of glyphosate and phosphate was also investigated by using 0.01 M KCl, 0.1 M KCl and 0.01 M CaCl2 as background electrolytes. Experiments showed that phosphate displaced adsorbed glyphosate from goethite, whereas glyphosate did not displace phosphate. Results also showed that the background electrolyte had a strong effect on phosphate adsorption, but little effect on glyphosate adsorption. Thus, there are differences between the adsorption of glyphosate and phosphate. The study also showed that 0.01 M KCl caused dispersion of goethite, resulting in inefficient filtering, and that phosphate precipitated as calcium phosphates in 0.01 M CaCl2 background electrolyte solutions. The results suggest that 0.1 M KCl is a more suitable background electrolyte to determine competitive adsorption processes involving glyphosate and phosphate.