This paper discusses the hitherto virtually unknown Byzantine cave monastery in the Ilgarini mağarası in the district of Pınarbaşı/Kastamonu based on its building remains, graffiti (mostly crosses), burials and notable finds. The remains were recorded during two brief surveys in 2012 and 2022. To shed light on the history of the site, an attempt is made to contex- tualise it within the mountainous regions of Middle Byzantine Paphlagonia, as well as with Middle Byzantine texts that relate to monasticism and might refer to the site. Research produces tentative evidence that the Ilgarini mağarası may be identified with the Chryse Petra known from several Byzantine texts, most prominently the Life of St Nikon Metanoite.

Seven sedimentary bentonite deposits were investigated in the Miocene series of the Pannonian Basin. The following stratigraphic and genetic characteristics were significant: (1) all deposits were formed within a transgressive series of a given Miocene sequence; and (2) it is possible that the source material of the bentonites is rhyolitic, confirmed by radiometric data proving simultaneous rhyolite tuff volcanism.

A detailed investigation on three lithologically different bentonite horizons within the same transgressive series was made at Sajoábaábony to determine the source material and to determine the causes of the differences. X-ray diffraction, differential thermal analysis and geochemical data of the different lithological types show that they all have rhyolitic source material, although in the case of the lowermost horizon the existence of reworked material from an underlying andesite tuff series is also presumed. The main difference is the degree of weathering. Considering the ratio between the amorphous phase and the montmorillonite, the amorphous volcanic glass can be regarded as the main source of the montmorillonite formation. The differences in the degree of alteration can be related to the changing characteristics of the tuff accumulation and the sedimentation. Transgression decreases the sedimentation rate allowing the optimal alteration of the amorphous phase. The increasing intensity of the tuff accumulation can also limit the bentonite formation because rapid deposition and burial present too little time for the optimal alteration of the amorphous phase.

Summarizing the results from the stratigraphic interpretation of the bentonite deposits and from the comparative analyses of the different bentonite horizons within the same transgressive systems tract, we can state that the relationship of the tectonic-related tuff accumulation and the eustasy-related sedimentation rate can affect both the possibility of bentonite formation in macro-scale and the degree of bentonitization in micro-scale.

Three kaolinite reference samples identified as KGa-1, KGa-1b, and KGa-2 from the Source Clays Repository of The Clay Mineral Society (CMS) are used widely in diverse fields, but the defect structures have still not been determined with certainty. To solve this problem, powder diffraction patterns of the KGa-1, KGa-1b, and KGa-2 samples were modeled. In a kaolinite layer among three symmetrically independent octahedral sites named as A, B, and C and separated from each other by b/3 along the b parameter, the A and B sites are occupied by Al cations, whereas, the C sites located along the long diagonal of the oblique kaolinite unit cell are vacant. The layer displacement vectors t1 and t2 are related by a pseudo-mirror plane from defect-free 1Tc kaolinite enantiomorphs, whereas, the random interstratification within individual kaolinite crystallites creates right-hand and left-hand layer sub-sequences producing structural disorder. A third layer displacement vector, t0, located along the long diagonal of the oblique layer unit cell that contains the vacant octahedral site and coincides with the layer pseudo-mirror plane may exist. Thus, a structural model should be defined by the probability of t1, t2, and t0 layer displacement translations Wt1, Wt2, and Wt0, respectively, determined by simulated experimental X-ray diffraction (XRD) patterns. X-ray diffraction patterns were calculated for structures with a given content of randomly interstratified displacement vectors, and other XRD patterns were calculated for a physical mixture of crystallites having contrasting structural order with only C-vacant layers. The samples differ from each other by the content of high- and low-ordered phases referred to as HOK and LOK. The HOK phase has an almost defect-free structure in which 97% of the layer pairs are related by just the layer displacement vector t1 and only 3% of the layer pairs form the enantiomorphic fragments. In contrast, the LOK phases in the KGa-1, KGa-1b, and KGa-2 samples differ from HOK phases by the occurrence probabilities for the t1, t2, and t0 layer displacements. In addition, the LOK phases contain stacking faults that displace adjacent layers in arbitrary lengths and directions. Low XRD profile factors (Rp = 8-11%) support the defect structure models. Additional structural defects and previously published models are discussed.

The preparation of porous materials from clay minerals by selective leaching is of interest because it yields residues with large specific surface areas that can be used as adsorbents of contaminants or as catalysts. Grinding produces surface modifications and therefore may significantly influence the leaching behavior. The aim of this paper is to study the effect of grinding and leaching on the structure of the vermiculite from Santa Olalla, Spain, using 57Fe Mössbauer spectroscopy, X-ray diffraction, infrared spectroscopy, and specific surface area (SBET) measurements. The study shows that grinding destroys the long range order of the vermiculite, but leaves the local structure in the environment of the Fe atoms intact, at least up to a grinding time of 10 min. The Mössbauer study shows that there is no Fe3+ in the tetrahedral sheets and that grinding does not lead to a significant oxidation of the structural Fe. Vermiculite ground for 4 min and leached with 1 M HCl solution at 80°C over a 24 h period was decomposed to X-ray amorphous silica with a very large specific surface area (SBET = 720 m2g−1) and with total pore volume of 0.586 cm3 g−1, whereas an unground sample leached with the same acid concentration yielded a specific surface area of only 504 m2 g−1. Most of the Mg2+ and Al3+ are removed from the ground sample after leaching with 1 M HCl, while large percentages of Fe2O3 remain with the X-ray amorphous silica. In unground vermiculite leached with 1 M HCl, a considerable amount of vermiculite remains in the residue. A sample ground for 4 min and treated with 0.25 M HCl also shows the typical vermiculite Mössbauer spectrum with an Fe2+/Fe3+ ratio similar to that of the unground vermiculite. The samples ground for 2 or 4 min and treated with 1 M HCl solution have an orange color and, according to the Mössbauer spectra, only Fe3+ remains. Mössbauer spectra of these samples taken at 4.2 K reveal the presence of akaganéite.

Secondary surface layers form by replacement of almandine garnet during chemical weathering. This study tested the hypothesis that the kinetic role of almandine’s weathering products, and the consequent relationships of primary-mineral surface texture and specific assemblages of secondary minerals, both vary with the solid-solution-controlled variations in Fe and Al contents of the specific almandine experiencing weathering.

Surface layers are protective (PSL) when the volume of the products formed by replacement is greater than or equal to the volume of the reactants replaced. Under such circumstances, reaction kinetics at the interface between the garnet and the replacing mineral are transport controlled and either transport of solvents or other reactants to, or products from, the dissolving mineral is rate limiting. Beneath PSLs, almandine garnet surfaces are smooth, rounded, and featureless. Surface layers are unprotective (USL) when the volume of the products formed by replacement is less than the volume of the reactants replaced. Under such circumstances, reaction kinetics at the interface between the garnet and the replacing mineral are interface controlled and the detachment of ions or molecules from the mineral surface is rate limiting. Almandine garnet surfaces beneath USLs exhibit crystallographically oriented etch pits. However, contrary to expectations, etch pits occur on almandine garnet grains beneath some layers consisting of mineral assemblages consistent with PSLs.

Based on the Pilling-Bedworth criterion, surface layers are more likely to be protective over a broad range of reactant-mineral compositions when they contain goethite, kaolinite, and pyrolusite. However, this combination requires specific ranges of Fe and Al content of the natural reacting almandine garnet. To form a PSL of goethite and kaolinite, an almandine garnet must have a minimum Al stoichiometric coefficient of ~3.75 a.p.f.u., and a minimum Fe stoichiometric coefficient of ~2.7 a.p.f.u.

Product minerals also influence the mobility of the least-mobile major rock-forming elements. A PSL consisting of goethite, gibbsite, and kaolinite yields excess Al for export during almandine garnet weathering. As the quantity of kaolinite present in the PSL decreases, the amounts of Al available for export increases.

Vermiculite is a common layered silicate clay mineral which has good adsorption and ion-exchange properties, and which is used to remove pollutants from groundwater. The adsorption by vermiculite from Heibei Province, China, of low-concentration ammonium in water was assessed here to evaluate the effects of adsorption time, particle size, adsorbent dose, pH, and temperature. Using Fourier-transform infrared spectroscopy, the concentration of NH4+ at 1430 cm−1 was evaluated after ammonium was adsorbed by vermiculite. Based on Langmuir-model analysis, the adsorption capacity of the Chinese vermiculite (in the particle-size range 0.025–0.075 mm) for ammonium was 18 mg/g after 3 h of equilibration. Optimal adsorption occurred at pH 6–7 and 60°C, which is different from that at high ammonium concentrations. Smaller particle-size fractions showed greater degrees of adsorption. Increase in Mg2+, K+, or Na+ concentrations influenced ammonium adsorption and, therefore, indicated that cation exchange was the mechanism for ammonium uptake from low-concentration solutions.

Hybrid Langmuir-Blodgett (LB) films of a single clay layer and a donor-(π-electron system)-acceptor (Dδ-π-Aδ−) zwitterionic molecule (ind-TCNQ), prepared from 1,3,3-trimethyl-2-methyleneindoline (donor) and 7,7,8,8-tetracyanoquinodimethane (acceptor) were prepared. The characteristics of the electrostatic interaction between the clay layer and the ind-TCNQ molecules were investigated. The amount of ind-TCNQ molecules spread onto the air-water interface was increased systematically so that mono- and multi-layers of the molecules could be formed on the clay layer. The hybrid LB films, which were deposited onto a solid substrate, were characterized by means of UV-vis absorption spectroscopy and optical second-harmonic generation measurement. The amount of ind-TCNQ molecules adsorbed on the clay layer increased with an increase in the amount of ind-TCNQ molecules spread onto the air-water interface. On the other hand, the SHG intensities of the films did not change with the change in amount of ind-TCNQ spread. The results indicate that the electrostatic interaction between the clay layer and the ind-TCNQ molecules operates only in the region where the ind-TCNQ molecules are in direct contact with the clay layer.

Diffraction effects from interstratified phyllosilicates have been studied extensively, and several computer programs such as NEWMOD© are available to facilitate interpretation of X-ray diffraction (XRD) profiles. However, accurate quantification of samples containing multiple interstratified phyllosilicate minerals is difficult due to the generally subjective nature of interpretations. More recent automated fitting interpretations require extensive computational effort, involving numerous calculations of profiles with different fitting-parameter values. Computational cost in time per calculation is the key factor influencing the overall efficiency of automated profile fitting. In general, the matrix methodology developed by Kakinoki and Komura is more efficient than the NEWMOD© architecture. A new matrix methodology was developed that reduces the number of matrix operations such as multiplication and addition, and these modifications improve calculation efficiency by up to a factor of three, with even greater improvement for small crystallite sizes (< 20 layers). A new computer program, ClayStrat, based on the modified matrix methodology, was developed to calculate one-dimensional XRD profiles from interstratified phyllosilicates along the Z direction.

The cation exchange capacity (CEC) is one of the most important properties of clays in terms of their performance in both natural and technical processes. For decades, common methods for determining exchangeable cations have failed when calcareous clays or soils were examined, because calcite is at least partly dissolved throughout the exchange experiment which in turn increases measureable Ca2+ concentrations. As a result, exchangeable Ca2+ and the sum of exchangeable cations by far exceed the amount of negative charges. In the past, the silver-thiourea method (AgTU) has been modified to overcome this problem (AgTUcalcite), but is unsatisfactory as the method is laborious. In the present study three new methods based on two alternative metal complexes, cobalt(III) hexamine (CoHex) and copper(II) triethylenetetramine (Cu-trien), are proposed. The optimum solid/liquid ratios of these methods and the optimum complex concentration of Cu-trien are reported, depending on the mineralogical composition of the samples. The key development is that the exchange solutions are saturated with respect to calcite prior to the experiment. Approximately 70–90% of the dissolution of calcite present as an admixture in a clay sample is suppressed in the subsequent cation exchange experiment, but not all. The Ca2+ exchange is not suppressed and there is no evidence for any precipitation of this Ca2+. Three possibilities for how to handle this problem are discussed, one of which is to perform no further correction. The resulting error arises from the remaining calcite solubility of the different solutions after pre-treatment with calcite. This corresponds to errors of 0.2–1.3 (CoHexcalcite)and 0.7–8.4 (Cu-triencalcite) meq/100 gCa2+ for samples with small and large CEC values, respectively. As a consequence of the poor performance of Cu-triencalcite for samples with large CEC, a more concentrated Cu-trien5 × calcite solution was developed which performed much better: 0.1–0.8 meq/100 g(Cu-trien5 × calcite). For Cu-trien5 × calcite and CoHexcalcite at least, the errors are in the range of the non-systematic scattering for exchangeable Ca2+ determination. Therefore, the methods suggested provide ‘operationally correct’ Ca2+ values without additional effort. Moreover, owing to the high selectivity of the index cations applied in the present study, only one exchange step is required, providing a significant advantage over the AgTUcalcite method.

As 1:1 dioctahedral clay minerals, kaolinite and halloysite have similar chemical compositions. However, halloysite often possesses a nanotubular structure and special surface reactivity compared to platy kaolinite. The objective of this current work was to determine the effect of the SiO2/Al2O3 ratio on the microstructure and properties of geopolymers derived from two kinds of kaolin: platy kaolinite and nanotubular halloysite. The chemical structures and compositions of the geopolymers obtained were characterized through X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR), whereas the microstructural analysis was performed by scanning electron microscopy (SEM), the Brunauer–Emmett–Teller (BET) method, and N2 physisorption analysis. The results indicated that calcined halloysite showed greater geopolymerization reactivity than calcined kaolinite. In addition, the mechanical properties of the clay-based geopolymers depended not only on the SiO2/Al2O3 ratio but also on the morphology of the clay. Crystalline zeolite A and geopolymer were produced after alkali-activation of kaolin with a SiO2/Al2O3 ratio of 2.5; these products possessed porous and heterogeneous microstructures having poor compressive strength. As SiO2/Al2O3 ratios increased to >2.5, geopolymers with compact microstructure and high compressive strength were produced after alkali-activation of kaolin. Notably, at a given condition, halloysite-based geopolymers exhibited greater early compressive strength, more compactness, and more homogeneous microstructure than kaolinite-based geopolymers. This can be attributed to the nanotubular microstructure of halloysite, which can release more Si and Al during alkali activation than platy kaolinite. These results indicated that the various morphologies and microstructures among clays have significant impact on the microstructure and compressive strength of geopolymers.

Caustic nuclear wastes have leaked from tanks at the US Department of Energy’s Hanford site in Washington State (USA) causing hundreds of thousands of gallons of waste fluids to migrate into the underlying sediments. In this study, four simulant tank waste (STW) solutions, which are high in NaOH (1.4 and 2.8 mol/kg), NaNO3 (3.7 mol/kg) and NaAlO2 (0.125 and 0.25 mol/kg), were prepared and reacted with reference kaolinite KGa-1 and KGa-2 at 50 and 80°C for up to 2 months. The structure and morphology of the resulting products were characterized using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. The products were also examined for cation exchange and Cs+ sorption as a function of ionic strength and types of cations in the background solutions. Cancrinite and sodalite were the only new minerals observed in all of the conditions tested in this experiment. Two major chemical processes were involved in the reactions: dissolution of kaolinite and precipitation of cancrinite and sodalite. Increasing NaOH concentration and temperature, and decreasing NaAlO2 concentration increased the transformation rate. Both cancrinite and sodalite appeared stable thermodynamically under the experimental conditions. The newly formed feldspathoids were vulnerable to acid attack and pronounced dissolution occurred at pH below 5.5. Cancrinite and sodalite can incorporate NaNO3 ion pairs in their cages or channels. Sodium in cancrinite and sodalite was readily exchangeable by K+, but less easily by Cs+ or Ca2+. The feldspathoid products sorb nearly an order of magnitude more Cs+ than the unaltered kaolinite. The Cs adsorption is reduced by competing cations in the background solutions. At low ionic strength (0.01 M NaNO3 or 0.005 M Ca(NO3)2), Ca2+ was more competitive than Na+. When the concentration of the background solution was increased 10 times, Na+ was more competitive than Ca2+.

Polytypism in gümbelite and its relationship to the fibrous or ribbon-like morphology exhibited by this Mg-rich illite were investigated by powder X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). Comparison between the XRD pattern from oriented fibers using a conventional powder diffractometer and a randomly oriented pattern using a Gandolfi camera suggested that 2M2 is dominant but other polytypes belonging to subfamily A also exist, and that the fiber axis of gümbelite is parallel to <110> in 2M2, <110> in 2M1, and <100> in 1M. The EBSD analyses confirmed these crystallographic directions directly from individual crystals. Electron diffraction and high-resolution TEM showed that twinning and intergrowths of various polytypes including both subfamilies are common in a single crystal and that the two types of rotations [2n60° and (2n+1)60°] between adjacent layers are often randomly mixed at the monolayer level. The data suggest that high densities of twinning and intergrowths account for the origin of the fibrous morphology along <110> for 2M1 and 2M2 polytypes. Volume restriction in a confined vein space may also play a role.

Samples from different depths in the Oligocene Frio formation (offshore Gulf of Mexico) were studied by X-ray diffraction (XRD), thermal analyses, and scanning electron microscopy. The experimental XRD patterns recorded from oriented and ethylene glycol (EG) solvated clay fractions of the samples were similar to those typical of random, mixed-layered illite-smectite (R0 I-S). The experimental XRD patterns recorded in air-dried (AD) and EG states were simulated using three different models. One of them corresponds to R0 I-S for which thickness and content of the interstratified layers were determined by the Środoń technique. The second model is represented by a single homogeneous I-S in which illite and smectite layers are interstratified with a tendency to segregation. The expandability of the segregated I-S model varies from 48% to 75% without any rational relationship between the smectite layer content and depth.

The third model assumes that the clay fraction is a physical mixture of smectite and an R0 I-S. In this model the I-S contains 65% illite and 35% smectite layers independent of depth, whereas the smectite content varies from 28% to 63%. This model has consistently smaller profile factors, Rp, for both EG and AD XRD scans compared with the Rp values determined for the other two models.

The mineralogical association, volcanic origin, narrow stratigraphic interval (427 m), and low maximum temperature (42°C) of the studied Frio Formation are considered. These features are completely consistent with the two-phase model and so the segregation model must be rejected. An authigenic origin of the pure smectite and an alternative detrital or authigenic origin of the R0 I-S are discussed.

The sizes and shapes of single clay mineral layers are difficult to determine though they are important parameters which determine the final properties of clay polymer nanocomposites and of ultrathin clay mineral films. To determine these sizes and shapes, hybrid monolayers of clay minerals (saponite, hectorite, Wyoming bentonite, and Laponite) and Rhodamine B octadecyl ester Perchlorate (RhB18) were prepared using the Langmuir-Blodgett (LB) technique and studied with atomic force microscopy (AFM). The AFM images reveal monolayers of elementary clay mineral layers, which are randomly oriented and have a wide range of sizes. The layers have typical shapes: lath-like for hectorite, plates for Wyoming bentonite, a mixture of laths and plates for saponite, and aggregates of very small layers of Laponite. Two types of layers were present in the LB films of saponite, Wyoming bentonite, and hectorite in a 40:60 ratio: (1) single layers 0.96 nm thick hybridized with RhB18; and (2) particles consisting of two clay layers with an intercalated monomolecular layer of water molecules and hybridized with RhB18. The Laponite particles in the hybrid LB films consist mainly of aggregates of two and three single layers.

Porous carbons rich in mesopores and with large pore volumes have been prepared by polymerization and carbonization of a carbon precursor, sucrose, within a matrix of the natural clay, halloysite. The carbon precursor was impregnated into the pores of halloysite and mostly deposited on the external surface of the halloysite rods during impregnation. The inorganic matrix was removed by washing the carbon-mineral composite with HF and HCl. The resultant carbons were characterized by nitrogen adsorption analysis and were found to possess a large specific surface area, a large total pore volume and significant mesoporosity, without an activation process being involved. The pore volume and mesoporosity were up to 1.86 cm3/g and 78%, respectively, even at low carbonization temperatures (500°C). The size of the mesopores of the resultant carbons is mainly between 3 and 30 nm and the dominant pore size is ∼3.7 nm. The carbonization temperature has significant effects on the pore-size distribution and structure of the resultant carbons and carbon-mineral composites, respectively. This process is relatively simple and expected to cost less than the high-temperature carbonization process in the preparation of mesoporous carbons with total pore volume and large specific surface areas.