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Knowing the influence of isomorphic substitutions on the acid-base properties of smectite edge surfaces is an important aspect of the detailed understanding of clay minerals' interfacial properties with implications in the modeling of adsorption processes. We investigated the intrinsic acidity constants of Fe(II)/Fe(III) and Al(III) substituted edge surface sites of montmorillonite with a cis-vacant structure, which includes four crystallographic orientations perpendicular to [010], [0 1 0], [110], and [ 1 1 0], using the first-principles molecular dynamics (FPMD) based vertical energy gap method. Fe(II) and Fe(III) substitutions resulted, respectively, in a significant increase and decrease in pKa values of amphoteric groups directly associated with Fe octahedra. In addition, Fe(II) substitution increased the pKa values of the neighboring silanol sites, while Fe(III) substitution had a weak influence on these sites. The Al-substituted tetrahedra had amphoteric sites with higher pKa values than the non-substituted Si tetrahedra, and they increased significantly the pKa values of the sites bridging the tetrahedral and octahedral sheets on surfaces perpendicular to [010] and [110]. The acid-base properties of substituted and non-substituted surface sites of cis-vacant montmorillonite were used to build a state-of-the-art surface complexation model, which successfully reproduced the best available experimental acid-base titration data. This model was further used to predict acid-base properties of dioctahedral smectites (montmorillonite, beidellite, and nontronite) according to their cis- or trans-vacant structures and their layer chemistry. According to these predictions, these smectites exhibit very similar overall pH buffering properties despite significant differences in structure and chemistry. A detailed analysis of the acid-base properties as a function of crystallographic directions demonstrated, however, that these differences should have a large influence on the adsorption of ionic species. [ABSTRACT FROM AUTHOR]

Using a complex of analytical methods, clay minerals were studied in Pleistocene sediments from Hole ODP 1038B (120.50 m deep), drilled on the northwestern edge of the Central Hill (Escanaba Trough, Gorda Ridge) near the hydrothermal source with a temperature of 108°C, as well as in Pleistocene background terrigenous sediments from reference Hole ODP 1037B, drilled in the Escanaba Trough 5 km south of the Central Hill. The terrigenous clay mineral assemblage in sediments from Hole 1037B consists of the mixed-layer smectite-illites, smectite, chlorite, illite, and kaolinite. Sediments from Hole 1038B in the interval from the bottom surface to a depth of 5–7 m are composed of terrigenous clay minerals. In the rest of the sedimentary section, clay minerals are represented by the newly formed biotite, chlorite, and dioctahedral smectite. They were formed during the basaltic melt intrusion into the Escanaba Trough with the formation of a laccolith and the subsequent rapid cooling of its flank. The intrusion was accompanied by the ascent of high-temperature hydrothermal fluid in the central discharge channel, interacting with the adjacent sediments. As a result, the fine-dispersed biotite was formed in sediments at the high-temperature stage of this interaction due to the primary terrigenous clay minerals, K-feldspar, and amphiboles. The rapid cooling of the hydrothermal fluid to a temperature of presumably 270–330°C promoted the partial replacement of biotite by chlorite. The further rapid cooling of the hydrothermal fluid to 200°C and lower and its mixing with seawater seeping into sediments of the Central Hill fostered the formation of smectite. [ABSTRACT FROM AUTHOR]

Three types of smectite with various crystallochemical compositions and interlayer cations as well as kaolinite and illite were fired at 800°C and 650°C and tested for their rehydroxylation's (RHX) potential and kinetics in the presence of water vapor at 200°C–350°C. A dehydroxylated structure of 2:1 Al‐rich mineral with the interlayer pillared by a large cation (like K+ or Cs+) is wide enough to allow H2O diffusion which results in advanced RHX, that is, restoring up to several tens of percent of the original OH content. Such 2:1 layer structures (beidellite, illite) do not follow the time‐to‐the‐quarter (TTTQ) kinetics during RHX and show a non‐Arrhenius behavior for isothermal RHX. Because TTTQ kinetics is assumed in an RHX dating of ceramic artifacts in archaeometry, fired‐clay ceramics prepared from material dominated by Al‐rich 2:1 minerals was found unfeasible for RHX dating. Kaolinite and Mg2+‐ or Ca2+‐exchanged smectites show the Arrhenius behavior and follow the TTTQ kinetics of RHX, resulting in apparent Ea increase with the progress of reaction (up to α ∼0.2) of ∼20–50 kJ/mol in beidellite and 15–35 kJ/mol in montmorillonite. We suggest using 'hydroxylation' rather than 'rehydroxylation' for structurally‐disordered fired clays gaining OH groups in an unknown position. [ABSTRACT FROM AUTHOR]

Fracture filling minerals and the smectite-group clay minerals in particular play a significant role in the geotechnical stability of the fractured rock mass. Smectites have multiple uses as geomaterials in waste management solutions, of which the most technically demanding is the geological disposal of radioactive waste. Here, the stability and occurrence of smectites as fracture filling minerals were studied with two main objectives: 1) to test the capability of short-wave infrared spectroscopy as a tool to streamline the site assessment where clay mineralogy needs to be characterised in detail, and 2) to provide a first assessment of naturally occurring smectites in various sample types collected from two Finnish sites (Olkiluoto and Hyrkkölä) and their potential as natural analogues of smectite stability for bentonite used in the engineered barrier systems of geological disposal repositories. The short-wave infrared (SWIR) method has been validated to be a useful tool in fracture mineral characterisation, specifically due to its fast acquisition and interpretation time compared to the conventional methods. The study confirms the in situ occurrence of smectites at both sites studied showing that, especially in Hyrkkölä, the smectite-group member is close to montmorillonite, the main constituent of bentonite. At Olkiluoto, the smectites studied show more interstratified features. The differences in the mode of occurrence are related to the history of their formation, especially hydrothermal alteration, and parent rock composition. Highlights: Fracture filling mineral analysis using short-wave infrared spectroscopy for site characterisation is non-destructive providing an efficient method for investigating large sample sets Fast data collection and interpretation from field for rock engineering can indicate presence of swelling minerals that may cause rock collapse Fracture filling smectites, specifically montmorillonites, provide natural analogues for bentonites used in geological disposal facilities for radioactive waste Short-wave infrared spectroscopy methods can partially exceed X-ray diffraction-based smectite identification especially for bentonites (e.g., beidellite vs. montmorillonite) which is important in quality assurance of bentonites used in geological disposal. [ABSTRACT FROM AUTHOR]

The smectite group of clay minerals (smectites) consists of negatively charged clay layers and interlayer exchangeable cations. They are spontaneously delaminated in water to form single clay layers when the interlayer cations are small alkaline cations such as Na+ or Li+. This phenomenon known as osmotic swelling has fundamental importance in constructing novel clay-based nanomaterials. However, osmotic swelling of smectites has not been systematically investigated in organic solvents although this phenomenon should be useful for developing novel clay-organic nanocomposites. We report herein that montmorillonite, a typical smectite, with monovalent and divalent inorganic interlayer cations shows osmotic swelling accompanied by delamination of clay layers in water-acetonitrile and water-2-propanol mixed solvents, although inorganic interlayer cations have been believed to be inappropriate for delamination of smectites in organic solvents. The delamination is confirmed by a combination of macroscopic sample appearances, XRD patterns, and SEM images. Montmorillonite with interlayer Na+ or Li+ ions shows osmotic swelling in pure water and the mixed solvents but not in pure organic solvents. Montmorillonite with alkaline earth dications in the interlayer spaces is swollen in water-organic mixed solvents but not in either pure water or organic solvents alone. Partial delamination in several systems can be clarified from SEM images even though the sample appearances and XRD patterns do not give firm evidence. Such non-uniform swelling behavior of montmorillonite is related to the disordered stacking of the aluminosilicate layers with different morphologies in the clay powders as observed by SEM. [ABSTRACT FROM AUTHOR]

The present study investigates the chemical weathering characteristics of an amphibolite enclave within granite from Bundelkhand region, central India. The mineral composition varies from core to rind with depletion of hornblende and plagioclase and enrichment of clay minerals and oxyhydroxides. The chemical index of weathering (CIA) indicates an incipient stage of weathering, within the enclave (CIA = 52.22 – 54.74). A-CN-K (Al2O3-CaO + Na2O-K2O) plot reveal samples plot along the A-CN line, indicating the removal of Ca and Na, due to plagioclase destruction. The weathering trend progresses towards the formation of smectite, a significant component within the clay composition of the enclave. The results of mass balance calculation reveal a substantial mass decrease of approximately 50% to 82% in the amphibolite. Furthermore, major oxides in the amphibolite enclave, experience significant losses. Trace elements display general losses in the enclave. This study provides valuable insights into the complex dynamics of elemental behavior during weathering by shedding light on the processes shaping the geochemical evolution of these rock types and their response to weathering conditions. [ABSTRACT FROM AUTHOR]

Bottom current activity has been responsible for the formation of a multitude of erosional and depositional features recorded in chalk. Advanced knowledge on the mobility and transport of unlithified calcareous nannofossil ooze by bottom currents is increasingly important not only for understanding the deposition of ancient chalk, but also for modelling the behaviour of modern pelagic carbonate sediments. Whereas the erosional behaviour of very pure calcareous nannofossil ooze has recently been investigated, the effect of organic matter and clay minerals on the erosional behaviour of calcareous nannofossil ooze is as yet unquantified. The results of the present study are based on laboratory flume studies utilizing chalk ooze with varying concentrations of smectite clay (1 to 30 wt.%), two types of organic matter and bed porosity. Phytoplankton (Pavlova lutheri) was used as a proxy for particulate marine organic matter, and xanthan gum as a proxy for extracellular polymeric substances. The results show a significant decrease in nannofossil ooze mobility with increasing content of clay or marine organic matter. Organic matter is found to reduce erodibility at much lower concentrations than clay minerals at porosities equivalent to those of the seafloor. At lower porosities, corresponding to some depth below the seafloor, organic matter and clay minerals are less effective in bed stabilization. This suggests that clay minerals and especially organic matter will affect the likelihood of initiation of severe erosion on the seafloor, whereas their inhibiting effect will decrease as erosion scours progressively deeper into the sediment column. The effect of extracellular polymeric substances is more complex than marine organic matter, probably due to detachment of large aggregates from the bed and resulting increase in bed roughness. The choice of organic matter in sedimentological experiments may lead to significant differences in sediment behaviour and should therefore involve careful consideration. [ABSTRACT FROM AUTHOR]

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Clay minerals have a great influence on the resulting properties of ceramic bodies. Fly ash as a waste material from burning black coal in power plants is a potentially valuable source of oxides (Al2O3, SiO2 or Fe2O3) for this production. Considering the process of ceramic firing, it is important to understand the thermal behavior of individual ingredients. The thermal behavior of natural smectite minerals (montmorillonite, beidellite, hectorite and nontronite) and their mixtures with added fly ash at different ratios (10%, 30% and 50%) was investigated. The phase analysis was obtained using X-ray diffraction and FT-IR spectroscopy. Under heating to 1200 °C, the structural changes of smectites were divided into four steps including dehydration, dehydroxylation, decomposition and crystallization of new phases. The addition of fly ash caused a shift in the reaction temperatures for all the mentioned phases. These changes were most noticeable for mixtures with hectorite; on the contrary, they were least noticeable for beidellite mixtures. Total mixture mass loss continually decreased with increasing fly ash amount. The obtained experimental thermal data can be applicable not only in the production of ceramic bodies or energy waste processing but also in construction and ensuring the safety of municipal waste landfills. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the mineral-associated organic carbon (MOC) and its relationship to clay minerals under different temperatures and precipitation. We selected three typical grassland transects in China: Titanium Plate (TP), Mongolian Plate (MP), and Loess Plate (LP) with natural temperature gradients. Along the transect, there is a gradient in the precipitation between the various types of grasslands. The surface soil (0–10 cm) was sampled to determine the MOC. Clay minerals were charactered by X-ray diffraction (XRD). According to the findings, the MOC content increased with decreasing temperature (5.41–14.89 g/kg). MOC had a positive correlation (r = 0.67) with the amount of clay mineral content. In the large-scale study of transects, precipitation masks the effect of temperature change on the MOC to a certain extent. It indirectly affected the MOC content by affecting the mixed-layer illite/smectite (I/Sme) content, and this effect was strongest at the lowest temperature TP (r = −0.73). Except for precipitation, CaO in the soil can affect soil organic carbon (SOC) stability by influencing the pH and I/Sme. The amount of bacteria increased as a result of I/Sme, and the influence of bacteria on the MOC was surpassed only by the soil pH. Climate and clay mineral composition characteristics affected the MOC to a certain extent. Among them, the effect of precipitation change on the MOC is higher than temperature, but it has little effect on soil with a higher weathering degree and CaO content. [ABSTRACT FROM AUTHOR]

Due to various historical events, in the Russian Federation, in addition to the radioactive waste storage facilities used in world practice, there are various nuclear and radiation hazardous facilities that require special procedures for monitoring and decommissioning. One of these facilities is the disposal site for LRW on the territory of the JSC Siberian Chemical Plant, where specially prepared waste is injected into sand reservoirs lying at depths of 300–350 m between clayey strata. This study examines in detail the features of the lithological and mineral composition of reservoir sands and aquitards. The processes of environmental transformation in reservoir sands, which lead to changes in the composition and structure of rocks, were characterized. These processes manifest themselves in the form of the development of leaching zones and their "healing" with newly formed smectite, the destruction of terrigenous grains, including the development of cracks, and the growth of newly formed smectite in the pore space of reservoirs. The forms of occurrence and localization of authigenic smectite formed as a result of technogenic impact are described. It has been shown that, despite the obvious impact of highly reactive solutions accompanying liquid radioactive waste, the insulating properties of the geological environment are maintained and even improved to some extent. [ABSTRACT FROM AUTHOR]

To investigate the influence of organic matter conversion on the evolution of organic matter pores, fractional conversion (TRHI) and loss of TOC (TOCL) from the organic matter conversion of Middle Jurassic Dameigou Formation shale samples were calculated using petrographic analysis. The TRHI of organic matter varies from 0.30 to 0.88 and TOCL content ranges from 0.62% and 4.09%. Relative to samples of Type III organic matter in shales, type II samples exhibit higher TRHI and TOCL values. Petrographic calculations of TRHI reveal that the fractional conversion of different kerogens differs for the same thermal maturity level. The specific surface area (SBET) ranges between 1.25 and 6.63 m2/g and micropore surface area (Smic) ranges between 4.16 and 21.27 m2/g. Correlations between pore structure parameters and TOCL content are higher than those between pore structure parameters and TOC content. The original TOC content decreases with increasing maturity level owing to hydrocarbon generation from organic matter conversion. The development of organic matter pores depends mainly on organic matter conversion, which is influenced by the richness, organic maceral compositions, and thermal maturity of the organic matter. The contents of kaolinite, illite, and mixed-layer illite/smectite (I/S) in the studied shales are 17.83%–37.05%, 5.36%–11.31%, and 5.27%–14.36%, respectively. Pore structure parameters (SBET and Smic) exhibit moderate positive correlations with illite content and I/S content, and moderate negative correlations with kaolinite content, indicating that different clay minerals have differential effects on pore structure. [ABSTRACT FROM AUTHOR]

REY‐rich mud, consisting of deep‐sea sediments with high concentrations of rare‐earth elements and yttrium (REY), holds significant economic potential. Many studies have been conducted on biogenic apatite, ferromanganese micronodule, and phillipsite within these deposits to ascertain the REY enrichment mechanisms. However, the knowledge of clay minerals in REY‐rich mud, which is the predominant component of pelagic sediments, is still limited. In this study, two adjacent gravity cores (core GC02: REY‐rich mud; core GC03: typical sediments of equatorial Pacific) were collected from the Clarion‐Clipperton Fracture Zone (CCFZ) of the Eastern Pacific to study the role of different clay minerals in REY enrichment. The clay minerals in core GC03 and core GC02 are primarily illite (averaging 60%) and smectite (averaging 63%), respectively, and the smectite in core GC02 was mainly Fe‐rich, which was probably formed via the reaction between opal and FeOOH. Moreover, multiple studies have reported similar smectite enrichment in REY‐rich mud, suggesting that it is a common characteristic. The presumed hydrothermal or volcanic origination of smectite in REY‐rich layers of core GC02 indicates the essential role of hydrothermal and volcanic activities in REY‐rich mud formation during the Oligocene in the western CCFZ. Key Points: Smectite is likely to be commonly enriched in rare‐earth elements and yttrium (REY)‐rich mud of the PacificAuthigenic smectite probably originated from hydrothermal or volcanic activity and concentrated moderate amounts of REYThe REY‐rich mud of the western Clarion‐Clipperton Fracture Zone presumably formed through hydrothermal or volcanic activities during the Oligocene [ABSTRACT FROM AUTHOR]

The mineralogical composition of Bobov Dol sub-bituminous coals from the lower part of the coal-bearing formation, was studied using optical microscopy, XRD and SEM-EDS analyses. Clay minerals (smectite, illite and kaolinite) and quartz, are the dominant minerals. Their characteristics indicate predominant terrigenous origin and argue for major detrital input from intermediate to mafic rocks. Accessory epigenetic barite-celestine mineralization, substituting almost completely oxidized siderite crystals and spheroidal aggregates, denotes circulation of meteoric aqueous solutions in the absence of other fracture-filing minerals. Finite glass spheres from the top of the coal seam I indicate synchronous volcanic activity, which did not influence peat formation. [ABSTRACT FROM AUTHOR]

A quantitative understanding of the molecular-scale mechanisms of radionuclide sorption on different clay minerals is crucial for the development and safe implementation of geological nuclear waste disposal technologies. We apply classical molecular dynamics (MD) computer simulations to study the adsorption of uranyl on the external basal surfaces of two typical clay models. In the illite model, negative charge is primarily localized in the tetrahedral sheets, while in the lower-charge smectite model, the isomorphic substitutions are introduced in the octahedral sheet. The comparison of atomic density distributions at the clay surfaces and adsorption-free energies profiles as a function of distance from these surfaces demonstrates that overall U behavior at the basal clay surface is quite similar for illite and smectite. Uranyl is sorbed as a mixture of outer-sphere aqua complexes [UO2(H2O)5]2+ and hydrolyzed aqua complexes [UO2(H2O)4–5OH]+ on both surfaces. The structural and compositional differences between the models do not greatly affect the uranyl's nearest coordination environment and are mainly reflected in the specific localization and orientation of the uranyl ions at both surfaces and in the magnitude of the adsorption-free energies. The observed quantitative characteristics of uranyl interactions with illite and smectite surfaces will help to better understand U behavior during the sorption process on clay minerals for the entire range of mixed-layer illite–smectite structures. A comparison of two versions of the ClayFF force field in the simulations made it possible to more accurately and quantitatively evaluate some subtle features of the uranyl–clay interactions and to obtain a more precise composition of uranyl complex with the modified ClayFF force field (ClayFF-MOH). [ABSTRACT FROM AUTHOR]

Smectitic clay minerals are unique indicators of paleoenvironmental conditions and exhibit a unique reactivity in the mineral world. Smectites may exhibit tetrahedral substitutions (Al3+, and sometimes Fe3+, can substitute for Si4+ in tetrahedral sites), resulting in a layer-charge increase, thereby impacting their properties (e.g. swelling and sorption capacities, catalytic properties, expandable abilities). The objective of the present study was to determine the influence of pH conditions on the hydrothermal production of smectite end-members exhibiting tetrahedral Al substitutions (saponite, beidellite, and nontronite), using X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) methods. The results of a series of syntheses conducted at various pH values allowed discussion of the crystallization pathways of these smectites from a mechanistic point of view. Altogether, the present study provided easily reproducible protocols for the hydrothermal production of pure saponite, nontronite, or beidellite (i.e. with no other mineral). The successful synthesis of pure saponite was achieved by exposing the starting gels to 230°C for 4 days in solutions at pH ranging from 5.5 to 14. The successful synthesis of pure beidellite was achieved by exposing the starting gels to 230°C for 9 days in a solution at pH 12. The successful synthesis of pure nontronite was achieved by exposing the starting gels to 150°C for 2.5 days in a solution at pH 12.5. Although extrapolating experimental results to natural settings remains difficult, the results of the present study may be of great help to constrain better the geochemical conditions existing or having existed on extraterrestrial planetary bodies. [ABSTRACT FROM AUTHOR]

The employment of clay minerals in the transport of water, nutrients, and contaminants depends on a few factors, including permeability, hydration behavior, ion-exchange efficiency, and more. With the application of external stress, it is still difficult to understand how clay particles swell and collapse, how water is retained, how hydration heterogeneities are formed within crystallites, and how interlamellar space is organized. The present work studied the link between geochemical, thermal, kinetic constraints (established at the laboratory scale), and intrinsic clay features by exchanging Na-rich montmorillonite (SWy2) with Ni2+, Mg2+, or Zn2+ cations. By comparing the experimental 00l reflections with the calculated reflections obtained from the structural models, quantitative X-ray diffraction (XRD) analysis has enabled the building of a theoretical profile describing the layer stacking mode (LSM) and allowed the description of interlayer space (IS) configuration along the c* axis. Regardless of the type of the exchangeable cations (EC), XRD modeling revealed that all samples exhibited interstratified hydration behavior within the crystallite size, which probably indicates partial or incomplete saturation of the IS. This theoretical result was defined by the appearance of two hydration states (1W and 2W), which were unrelated to the strain strength creating a higher degree of structural heterogeneity. Using the theoretical decomposition of the observed XRD patterns, the identification of all distinct layer populations and their stacking mode was achieved. The segregated LSM are, therefore, obviously superior as a function of stress strength. [ABSTRACT FROM AUTHOR]

Microbially induced formation and transformation of clay minerals are known to be ubiquitous in nature. This work investigated the smectite-to-kaolinite transformation by Bacillus mucilaginosus, a kind of silicate-weathering bacterium. Results showed that the microbe-smectite system doubled protein production compared with the abiotic controls and enhanced dissolved 1.6% of total Si and 0.9% of total Al from smectite after the 25 days experiment. The formation of kaolinite was verified through its distinguished d(001)-spacing of 0.710 nm revealed by synchrotron radiation X-ray difrac-tion (SR-XRD) and high-resolution transmission electron microscope (HR-TEM). HR-TEM analysis indicated some mixed layers of smectite and kaolinite appeared in the form of a super-lattice structure. Moreover, the compositional and morphological changes of the solids suggested the emergence of kaolinite was associated with the formation of amorphous SiO2 and fragmented clay particles with lower Si/Al ratio and exposed crystal edge. Based on the detection of –C=O species on the smectite surface and the decrease of pH from 8.5 to 6.5, we inferred the organic ligands secreted by Bacillus mucilaginosus complexed with cations, especially for Si, which stripped the tetrahedral sheets and promoted the kaolinization of smectite. To our knowledge, this is the first report of microbially induced smectite-to-kaolinite transformation under ambient conditions in a highly-efficient way. This work could shed light on a novel pathway of microbe-promoted weathering of smectite to kaolinite at the Earth surface conditions. Such a robust and eficient transformation from expansive smectite to non-expansive clays as kaolinite may be of great potential in enhancing oil recovery in reservoirs. [ABSTRACT FROM AUTHOR]

Abstract REY‐rich mud, consisting of deep‐sea sediments with high concentrations of rare‐earth elements and yttrium (REY), holds significant economic potential. Many studies have been conducted on biogenic apatite, ferromanganese micronodule, and phillipsite within these deposits to ascertain the REY enrichment mechanisms. However, the knowledge of clay minerals in REY‐rich mud, which is the predominant component of pelagic sediments, is still limited. In this study, two adjacent gravity cores (core GC02: REY‐rich mud; core GC03: typical sediments of equatorial Pacific) were collected from the Clarion‐Clipperton Fracture Zone (CCFZ) of the Eastern Pacific to study the role of different clay minerals in REY enrichment. The clay minerals in core GC03 and core GC02 are primarily illite (averaging 60%) and smectite (averaging 63%), respectively, and the smectite in core GC02 was mainly Fe‐rich, which was probably formed via the reaction between opal and FeOOH. Moreover, multiple studies have reported similar smectite enrichment in REY‐rich mud, suggesting that it is a common characteristic. The presumed hydrothermal or volcanic origination of smectite in REY‐rich layers of core GC02 indicates the essential role of hydrothermal and volcanic activities in REY‐rich mud formation during the Oligocene in the western CCFZ.

Exploring reservoir stratum sensitivity is an important basic work for oil and gas exploration and exploitation, in which the degree of water sensitivity damage is often affected by the clay mineral content and microscopic pore throat structure of illite/montmorillonite mixed clay minerals. To reveal the distribution law and the main controlling factors of illite/montmorillonite mixed layers, the diagenesis, regional distribution law, and main controlling factors of illite/montmorillonite mixed layers in the reservoir stratum of the Upper Wuerhe Formation in the study area were analyzed by high-resolution testing techniques such as scanning electron microscopy (SEM) and Advanced Mineral Identification and Characterization System. Diagenesis was the main cause of illite/montmorillonite mixed layers in the study area, and the occurrence state under SEM was mostly flaky, silky, and flocculent filling in intragranular dissolved pores or intergranular pores. The mass fraction of illite/montmorillonite mixed layers increased with the increase in depth in the longitudinal direction, which was closely related to the sedimentary microfacies and the hydrodynamic environment in the plane. Results show that potash feldspar is the material basis for the formation of illite/montmorillonite mixed layers, and the strength of the hydrodynamic environment is the main controlling factor for the quality distribution characteristics of such mixed layers. This study provides a new technical method and research idea for understanding the reservoir sensitivity characteristics, which has good guiding significance for the blocks with strong reservoir sensitivity. The original pore structure of the reservoir can also be protected against destruction by various sensitivity factors in the developmental stage caused by the unclear understanding of the spatial distribution characteristics of clay minerals affecting the yield in oil and gas field development. [ABSTRACT FROM AUTHOR]

The results of investigations of the behavior of analcime-containing rocks of Timan (Komi Republic) at high temperatures (1200 – 1280°C) are brought forward. The mineral composition and physical characteristics of the resulting ceramics were determined: apparent density, water absorption, open porosity, and thermal conductivity. The influence of the mineral composition of the initial analcime-containing rocks on the foaming capacity and physical characteristics of fired ceramics is demonstrated. Porous materials with low apparent density (0.37 – 0.39 kg/m3), water absorption (up to 4.3%), and thermal conductivity (0.09 – 0.10W/(m · K)) have been obtained. The results show the prospects of using analcime-containing rocks of a certain mineral composition for the production of heat-insulating foam materials. [ABSTRACT FROM AUTHOR]

Synchrotron powder diffraction data is presented for a series of relatively phase-pure smectite clay mineral standards obtained from the Clay Minerals Society. Rietveld refinement using a model for turbostratic disorder was performed to estimate the lattice parameters and mineral impurities in the smectite standards. Bragg reflection lists and raw data have been provided for inclusion in the Powder Diffraction File. [ABSTRACT FROM AUTHOR]

A geological, mineralogical, and geochemical characterization of the Tamame de Sayago (Zamora, Spain) deposit was carried out with the aim of knowing the conditions that facilitated the genesis in the same deposit of kaolinite and smectites. The alteration processes affecting a Variscan granite were deduced throughout the study of a very wide group of representative samples by X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analyses of major, minor, and trace elements, as well as δ18O, δ34S stable isotope and K/Ar dating analyses. In addition, 2D and 2.5D graphs of the kaolinite and smectite isoconcentrations were obtained from core data. According to the color and texture, two different clayey rock types were identified and named as homogeneous alteration zones (ZAHO) and heterogeneous alteration zones (ZAHE). The ZAHO are regoliths in which the granite texture is preserved, and the feldspars are almost completely kaolinized. In the ZAHE, the original texture of the granitic rock is lost, and the main clay mineral is smectite. The mineralogical composition is similar, with kaolinite, smectite, mica, quartz, scarce feldspar, and occasionally natroalunite and APS (aluminum-phosphate-sulphate); however, the mineral concentration varies considerably because ZAHO are rich in kaolin areas whereas ZAHE are bentonitic areas. Both rock types contain numerous veins and nodules. The weathering of the Paleozoic granite alongside the absence of sedimentation during the Mesozoic led to the formation of kaolinite that is preserved in ZAHO materials. Nonetheless, during the Cretaceous–Tertiary transit, the conditions of tectonic stability varied. Late Variscan faults reactivated which allowed the percolation of Mg- and Ca-rich hydrothermal fluids through the already kaolinized granite, increasing the alteration of the primary silicates and leading to the formation of smectites in ZAHE materials. The amount of smectites is greater closer to the faults. The stable isotopes indicate the meteoric nature of the low-temperature hydrothermal fluids. The K/Ar data obtained from the natroalunite of veins indicate that those hydrothermal fluids circulated in different pulses from 66.4 ± 1.7 to 58.8 ± 1.5 Ma, as a minimum. Those ages are coincident with the first formation stages of the Duero Basin. [ABSTRACT FROM AUTHOR]

Clays are fine‐grained rocks that form in the presence of water. Their occurrence typically depends on a combination of geological setting and geochemical conditions. The widespread and diverse clay deposits identified on Mars indicate that the planet experienced multiple episodes of water activity, especially in the early period. The characterisation of Martian clays will reveal key information on geological history, the past climatic conditions and the overall habitability of Mars. Among the analytical techniques typically utilised for such mineralogical characterisation, Raman spectroscopy will be applied for the first time during several robotic exploration missions of Mars in the 2020s. In this study, various clay‐rich samples from Westerwald, Germany were analysed to help inform mission operations and interpretation of data returned by the miniaturised Raman instruments. The samples, as verified by infrared spectroscopy, constitute kaolinites, Al‐rich smectites and Fe/Mg‐rich smectites, which are relevant to the clay mineralogy expected at Martian landing sites (Jezero crater and Oxia Planum). Despite the levels of fluorescence experienced during Raman measurements of the clay‐rich powder samples when using a 532 nm laser, the Raman signatures of phyllosilicates were identified for kaolinite and several different types of smectite (e.g. montmorillonite, nontronite, saponite) in these complex dispersions. Following these measurements, identification of various accessory minerals disseminated in the clay matrix was also achieved using the micro‐Raman system. Finally, a brief discussion concerning the analytical strategies for successful clay analyses using miniaturised Raman instruments is provided. [ABSTRACT FROM AUTHOR]

Using the through diffusion method at room temperature, the migration of radionuclides (3H, 99Tc, 137Cs, 233U) in compacted samples of clay materials was studied through pore diffusion from a model leachates of phosphate matrix of radioactive waste with a total salt content of about 400 mg/L. The effective diffusion coefficients and sorption distribution coefficients of radionuclides for the studied clay barrier materials were determined based on the experimental results. The patterns of diffusion transfer of tritium, cesium and uranium were revealed depending on the structure, mineral composition of clay materials and the content of radionuclides in the pore solution. Numerical solutions are proposed for calculating the effective pore diffusion coefficients of these radionuclides. There are not yet enough data to analyze the factors influencing the diffusion of technetium. [ABSTRACT FROM AUTHOR]

Clay minerals are among the most important reactive components of soil systems, acting as a bridge linking organic and inorganic components. Lithology is a key factor in clay-mineral genesis and transformation, yet it has received scant attention to date at the nanoscale. Inferences regarding pedogenic clay-mineral transformations based on X-ray diffraction (XRD) are sometimes speculative, whereas mineralogic relationships documented by high-resolution transmission electron microscopy (HRTEM) are more robust due to direct evidence from lattice-fringe observations. In this contribution, the mineralogical and geochemical characteristics of four soils derived from different parent rock types (a gneiss, an Fe-rich siltstone, a sandstone, and a dolostone) from subtropical China were determined using HRTEM, XRD, and geochemical elemental data. The predominance of 2:1 clay minerals and kaolinite in the investigated soils is typical of subtropical climatic settings. Lattice-fringe images suggest the prevalence of topotactic transformations during clay-mineral alteration. Two distinct alteration pathways were observed in the investigated soils, one starting with chlorite and the other with illite, with convergence of mineralogic compositions toward kaolinite and crystalline iron and aluminum (oxyhydr)oxides. In the early stages of weathering, chlorite transformed into expandable clays through a continuous, solid-state mechanism with corrensite and/or randomly interstratified chlorite-vermiculite/chlorite-smectite as intermediate products. Unlike chlorite, which tends to form a 1:1 regularly interstratified phase, the weathering of illite commonly starts at layer edges. Under subtropical monsoonal climates, the precursor minerals in host rocks and aeolian materials determine the starting composition and, to a certain extent, the trajectory of clay-mineral transformation over time. With advanced weathering, mineralogic convergence toward kaolinite and Fe/Al-(oxyhydr)oxides tends to obscure the initial substrate composition. This study advances our understanding of the role of parent lithology in clay-mineral evolution at the nanoscale. [ABSTRACT FROM AUTHOR]

Volcanic glass and its mixture with smectite are commonly observed in shallow parts of subduction zones. As volcanic glass layers often act as glide planes in submarine landslides, and because its alteration product, smectite, is one of the frictionally weakest geological materials, the frictional characteristics of volcanic glass‐smectite mixtures are important for fault slip behavior in shallow parts of subduction zones. We performed a series of friction experiments on volcanic glass‐smectite mixtures with different smectite contents from 0% to 100% at various velocity conditions from 10 μm/s to 1 m/s under an effective normal stress of 5 MPa and pore pressure of 10 MPa. In general, apparent friction coefficients negatively depend on the smectite content at any velocity tested. We found that samples with smectite contents of 15%–30% showed a drastic slip‐weakening behavior at intermediate velocities of 1–3 mm/s. Finite element method modeling shows that thermal pressurization does not contribute to the observed weakening behavior. The critical nucleation length estimated from the slip‐weakening behavior is approximately 1–10 km, which is large enough to prevent the slip to accelerate to seismic slip velocity. Therefore, gouges with minor amount of clay, such as subducting volcanic ash layers, may contribute to the occurrence of the slow earthquakes at shallow depths in subduction zones. Plain Language Summary: Materials erupted from volcanoes deposit on the seafloor and subduct at the trench. One such material, volcanic glass, easily alters into mechanically weak clay minerals such as smectite that can cause an enormous slip during an earthquake in subduction zones. In this study, we experimentally examined the frictional properties of mixtures of volcanic glass and smectite to elucidate fault slip behavior at shallow depths of subduction zones. Experiments with varying smectite content showed that a drastic reduction in fault frictional strength was induced when a small amount of smectite was present at moderately high velocity conditions. This behavior may induce slow earthquakes in shallow subduction zones. Key Points: Small amount of clay minerals in volcanic glass induces a drastic slip‐weakening at ∼1 mm/sThermal processes do not contribute to the weakening behaviorSlip weakening and large critical nucleation length at intermediate slip velocities might cause slow earthquakes [ABSTRACT FROM AUTHOR]

Parent material and topography are among the soil-forming factors that affect soil evolution by influencing different parameters. This study was conducted to compare the effect of marl and calcareous parent materials in different slope positions, including the summit, shoulder, foot-, and toe-slopes on soil clay mineralogy in the Karoon 3 Basin, east of Khuzestan Province. Four soil profiles in each of the two topo-sequences were dug. They were sampled based on their genetic horizons and some physical, chemical properties, and clay mineralogy were measured. The results showed that the type and abundance of clay minerals identified for both parent materials were more affected by topo-sequence position. The composition of minerals identified in the topo-sequence with marl parent materials included kaolinite, palygorskite, smectite, chlorite, mica, and quartz, and in the topo-sequence with calcareous parent materials, palygorskite, smectite, chlorite, mica minerals, and quartz, and most of the identified minerals were also observed in all positions in the C horizon. However, in marl parent materials kaolinite, and calcareous parent materials, smectite seems to have been formed pedogenically. The result of the association between Weaver and Beck indicated that most of the clay minerals are in the equilibrium of Palygorskite. [ABSTRACT FROM AUTHOR]

Due to various historical events, in the Russian Federation, in addition to the radioactive waste storage facilities used in world practice, there are various nuclear and radiation hazardous facilities that require special procedures for monitoring and decommissioning. One of these facilities is the disposal site for LRW on the territory of the JSC Siberian Chemical Plant, where specially prepared waste is injected into sand reservoirs lying at depths of 300–350 m between clayey strata. This study examines in detail the features of the lithological and mineral composition of reservoir sands and aquitards. The processes of environmental transformation in reservoir sands, which lead to changes in the composition and structure of rocks, were characterized. These processes manifest themselves in the form of the development of leaching zones and their “healing” with newly formed smectite, the destruction of terrigenous grains, including the development of cracks, and the growth of newly formed smectite in the pore space of reservoirs. The forms of occurrence and localization of authigenic smectite formed as a result of technogenic impact are described. It has been shown that, despite the obvious impact of highly reactive solutions accompanying liquid radioactive waste, the insulating properties of the geological environment are maintained and even improved to some extent.

Clay minerals are usually considered as important indicators to identify sources in both terrigenous and marine sediments. In particular, clay minerals in metalliferous sediments (MS) have long been studied in global oceans except in South Mid-Atlantic Ridge (SMAR) due to limited explorations. Thus, 32 MS and 34 non-MS (NMS) samples were analyzed to clarify the distribution characteristics and mineral compositions of clay minerals. All the sediments were collected along the SMAR between 12°S and 27°S. After removal of organic matter and carbonate, clay fractions (<2 µm) were investigated by X-ray diffraction (XRD) analysis. Results show that clay mineral assemblages of surface MS consist dominantly of smectite, less abundant illite, chlorite, and kaolinite in average weight percentage of 30%, 21%, 18%, and 16%, respectively. On the other hand, clay mineral assemblages in the NMS consist mainly of illite, less abundant kaolinite, chlorite, and very scarce smectite in average weight percentage of 47%, 29%, 24%, and 0.2%, respectively. The clay fractions in MS are mainly composed of amorphous or poorly crystallized Fe/Mn oxyhydroxides, clay mineral, quartz, and plagioclase. However, the counterparts in the NMS are mainly composed of well-crystallized clay minerals, quartz, and plagioclase without the presence of Fe/Mn oxyhydroxides. It is suggested that most of the illite, kaolinite, and chlorite in both MS and NMS are likely aeolian dust in origin from South Africa continent. In addition, the abundance of kaolinite dominates the clay mineral assemblage at low latitudes, where the intensive chemical weathering of continental source rocks facilitating the formation of kaolinite. In terms of smectite, it is indicated of authigenic origin in consideration of only smectite is available in several MS and the absence in NMS. Moreover, the MS samples with only smectite available are always accompanied by goethite. Therefore, it is assumed that most of smectite occurred in studied area is the results of interaction between hydrothermal Fe-oxyhydroxide, silica, and seawater. [ABSTRACT FROM AUTHOR]

Smectites, like other clay minerals, have been shown to promote ice nucleation in the immersion freezing mode and likely contribute to the population of ice-nucleating particles (INPs) in the atmosphere. Smectites are layered aluminosilicates, which form platelets that depending on composition might swell or even delaminate in water by intercalation of water molecules between their layers. They comprise among others montmorillonites, hectorites, beidellites, and nontronites. In this study, we investigate the ice nucleation (IN) activity of a variety of natural and synthetic smectite samples with different exchangeable cations. The montmorillonites STx-1b and SAz-1, the nontronite SWa-1, and the hectorite SHCa-1 are all rich in Ca 2+ as the exchangeable cation; the bentonite MX-80 is rich in Na + with a minor contribution of Ca 2+ , and the synthetic Laponite is a pure Na + smectite. The bentonite SAu-1 is rich in Mg 2+ with a minor contribution of Na + , and the synthetic interstratified mica-montmorillonite Barasym carries NH 4+ as the exchangeable cation. In emulsion freezing experiments, all samples except Laponite exhibited one or two heterogeneous freezing peaks with onsets between 239 and 248 K and a quite large variation in IN activity yet without clear correlation with the exchangeable cation, with the type of smectite, or with mineralogical impurities in the samples. To further investigate the role of the exchangeable cation, we performed ion exchange experiments. Replacing NH 4+ with Ca 2+ in Barasym reduced its IN activity to that of other Ca-rich montmorillonites. In contrast, stepwise exchange of the native cations in STx-1b once with Y 3+ and once with Cu 2+ showed no influence on IN activity. However, aging of smectite suspensions in pure water up to several months revealed a decrease in IN activity with time, which we attribute to the delamination of smectites in aqueous suspensions, which may proceed over long timescales. The dependence of IN activity on platelet stacking and thickness can be explained if the hydroxylated chains forming at the edges are the location of ice nucleation in smectites, since the edges need to be thick enough to host a critical ice embryo. We hypothesize that at least three smectite layers need to be stacked together to host a critical ice embryo on clay mineral edges and that the larger the surface edge area is, the higher the freezing temperature. Comparison with reported platelet thicknesses of the investigated smectite samples suggests that the observed freezing temperatures are indeed limited by the surface area provided by the mostly very thin platelets. Specifically, Laponite, which did not show any IN activity, is known to delaminate into single layers of about 1 nm thickness, which would be too thin to host a critical ice embryo. [ABSTRACT FROM AUTHOR]

The properties of one type of clay from the Orenburg Oblast are considered so as to determine its applications in industry. The mineral and chemical compositions as well as the dispersivity were determined, and an assessment was made of its degree of sintering. It was determined that the Orenburg Oblast clay is basic, with a high content of coloring oxides, and has medium dispersivity, it is moderately plastic, well-dried, and insensitive to desiccation. The mineral composition of the clay was determined. It was found that the main phases are kaolinite, smectite, illite, and quartz. Possible areas of application in the production of ceramic were identified. This clay can be used for the production of ceramic tiles of groups AII (b-1, b-2), AIII, BII (b), and BIII (GOST 13996–2019), ceramic bricks of grade M200 and higher (GOST 530–2012), and ceramic tiles (GOST 56688–2015). [ABSTRACT FROM AUTHOR]

The intercalation of tris-chelate metal complexes into clay minerals, in particular smectite, has attracted broad attention in terms of photochemistry, catalysis, and chiral recognition. It is of interest that they exhibit different adsorption behavior between racemic and enantiopure states on natural smectite. Their adsorption structure in the interlayer space has been, however, the topic of debate. In this short review article, my approach to clarify the adsorption structure of chiral metal complexes is described. The XRD method in a transmission mode was applied for the hybrid samples of montmorillonite and racemic tris-chelate nickel complexes, which were confined in a capillary tube. When the amount of adsorbed Ni complexes exceeds the cationic exchange capacity of montmorillonite, the obtained hybrid samples exhibit anisotropic diffraction in the 2D XRD images. The newly observed peaks were attributed to the reflections from the (10), (11), and (21) planes of the hexagonal assembly of Ni complexes. Based on the results, the detailed arrangement of racemic Ni complexes in the clay interlayer space is also discussed. [ABSTRACT FROM AUTHOR]

Closely interbedded mudstone and sandstone are rarely the focus of clay mineral diagenetic studies; as such, it is not understood if these various rock types follow the same or different diagenetic pathway(s) during burial. Over a depth span of ~2,300 to 4,200 m, 95 core samples of alternating Pennsylvanian mudstone/sandstone from the hydrocarbon‐rich Anadarko Basin in Oklahoma have been characterized petrographically, mineralogically, and chemically. The investigated fine‐grained sediment is argillaceous to siliceous mudstone, dominated by Illite/mica and mixed‐layer illite–smectite. The sandstone is variably classified as quartz and mudclast‐rich litharenite to sub‐litharenite, which is commonly carbonate‐cemented. This contribution provides evidence for a very similar diagenetic evolution of the clay mineral assemblages across all rock types despite the discrepancies in porosity and permeability of the host rock. We posit that the incorporation of micrometre‐scale mudclasts through bioturbation of the sandstone may explain the relatively uniform compositional characteristics of illite–smectite, chlorite, and kaolinite. Inferences are drawn from a detailed clay mineral quantification of these interbedded lithologies aid to our understanding of the clay mineral distribution and speciation in Pennsylvanian strata of the Anadarko Basin, which further helps to constrain the reservoirs' physical, chemical, and structural properties. [ABSTRACT FROM AUTHOR]

Aseismic slip is a stable fault slip, which allows strain to be relieved smoothly. Aseismic slip prevents the earthquake propagation, but it could nucleate an earthquake elsewhere. Understanding the mechanism of aseismic slip is promising in revealing the seismic cycle. Experimental evidence showed clay-rich fault gouge bears a low-friction strength, and the friction is strengthened with slip velocity (velocity-strengthening), which was thought to support aseismic slip. Clay minerals are comprised of platy crystalline layers with water intercalated between them, which may act as a lubricant. Sliding between clay layers was suspected to support aseismic slip but lacked a clarified mechanistic insight. We use non-equilibrium molecular dynamics simulations to show that shear-induced interlayer sliding is frictionally weak and velocity-strengthening, which evidences the role of clay minerals in aseismic slip. We find that interlayer water is a viscous fluid at most times, which explains the shear response of interlayer sliding. Depending on temperature and pressure conditions, intercalated water can be monolayer or bilayer, fluidic or ice like. Shear induces icelike water to transform into fluidic water, which happens as a stick-slip phenomenon reflecting a first-order transition. Increased pore fluid pressure leads to the transformation from monolayer to bilayer intercalated water, resulting in a lower friction strength and enhanced velocity-strengthening behavior. Our work suggests that disclosing the hydration state of a clay mineral is preliminary when studying fault mechanics. [ABSTRACT FROM AUTHOR]

The establishment of quality requirements of clay-based products, for medicinal, wellness, and aesthetic purposes, is mainly sustained by the good interactions between the clay-based formulation and the skin. The release of ionizable elements and their availability to percutaneous absorption should be, ideally, physiologically effective during passive percutaneous absorption. Clay-based products are promoted in the European market as therapeutic clays or aesthetics, which is labeling that combines characteristics of medicinal products along with cosmetics. Different countries regulate these products under different legal frameworks. This study focuses on the mineralogical, chemical, and technological characterization of some clay-based products available on the market, designed for topical use, framed in the peloids concept, and claimed as natural products. The main goals are to contribute to the establishment of clay-based products quality criteria as reliable scientific information, aiming for the compliance of intended use, the information for the potential health hazards and toxicological effects of clay-based products, and the distinction in what concerns therapeutic compliance and aesthetic or wellbeing product certification. There were 13 clayed products for cosmetic purposes, available online and in commercial stores, together with three thermal peloids, that were studied. Mineralogical composition of the 16 studied samples reveals a polymineralic association with the presence of variable quantities of quartz, calcite, and feldspars, whereas clay minerals are not predominant and characterized by the presence of clay-based fraction content, composed mainly by illite, smectite, and kaolinite in variable amounts and with several mineral associations. The clay-based products contain median values of 17 ppm As, 315 ppm Ba, 79 ppm Cr, 11 ppm Co, 29 ppm Pb, 26 ppm Ni, and 62 ppm Zn. One sample presented 4.1 ppm of Cd. The studied samples have safety concerns about specific limits of As, Ba, Cd, Cr, Co, Pb, Ni, and Zn which are above the regulated avoidable limits. Samples' pH is out of range of skin's natural pH as well. [ABSTRACT FROM AUTHOR]

The long-term safe storage of CO2 in geological reservoirs requires the understanding of the impact of CO2 on clay-rich sealing cap rocks. The reactivity of the mixed layer of illite-smectite was investigated to determine the reaction pathways under conditions of supercritical CO2 (scCO2) conditions in the context of geological CO2 storage. A common clay (blue marl from the Guadalquivir Tertiary basin, southern Spain) was tested under brine scCO2 conditions (100 bar and 35 °C) for 120 and 240 h. The clay sample (blue marl) contains calcite, quartz, illite, smectite, and the corresponding mixed-layer and kaolinite. X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses were performed. The illitization of mixed-layer illite-smectite was observed by XRD and confirmed by a variation in the content of different elements (K, Mg, Na, Ca, and Fe) of the transformation, as well as an increase in the specific surface (SSA) of the clay (36.1 to 38.1 m2/g by N2, 14.5 to 15.4 m2/g by CO2 adsorption). Furthermore, these reactions lead to mineral dissolution and secondary mineral formation along the CO2–water–clay intercalations of the source rock were responsible for a change in porosity (7.8 to 7.0 nm pore size). The implications of illitisation, mineral destruction, and precipitation processes on CO2 storage and clay layer integrity should be explored before deciding on a geological storage location. [ABSTRACT FROM AUTHOR]

The International Ocean Discovery Program cored Sites U1517 (Tuaheni landslide) and U1519 (Tuaheni Basin) on the Hikurangi slope, North Island, New Zealand. We employed X‐ray diffraction to document clay mineral assemblages within the muddy sediments, with the aim of testing their potential influences on slope stability. Detrital smectite dominates the clays, with average proportions of 52 wt% at Site U1517 and 53 wt% at Site U1519. Bulk sediment from Site U1517 contains up to ∼29 wt% smectite (average = 21 wt%), high enough to reduce the angle of internal friction (on average) to ∼6°. Stratigraphic sections at both sites are homogeneous; compositional excursions are not evident along inferred slip surfaces or weak layers. Smectite decreases in the "downstream" direction of the East Cape Current, and that spatial trend correlates with lower densities of slide scars. The uniformity of compositional preconditioning, however, points to other factors as determinants of slip nucleation. Plain Language Summary: Expandable clay minerals (smectite) are notorious for weakening sediments and contributing to conditions that promote landslides. The Hikurangi margin offshore North Island, New Zealand, is noted for its abundance of submarine landslides. To assess their possible causes, we analyzed clay mineral assemblages from two sites on the upper trench slope that were sampled by the International Ocean Discovery Program. Cores from Sites U1517 and U1519 display unusual degrees of compositional homogeny, with smectite as the dominant clay mineral. We did not find any compositional anomalies at inferred slip surfaces or along weak layers of the Tuaheni landslide. Instead, the entire stratigraphic succession appears to be relatively weak. With inherited preconditioning, dynamic loading during large earthquakes is probably enough to trigger landslides, especially on steeper slopes. Key Points: Hikurangi trench‐slope sediments, including muds within the Tuaheni landslide complex, contain high concentrations of detrital smectiteSmectite is abundant enough to reduce the bulk sediment's coefficient of friction, with little stratigraphic variabilityThe homogeneous mud composition results from strong currents and does not change significantly along inferred slip surfaces or weak layers [ABSTRACT FROM AUTHOR]

The Bursa-Orhaneli and Keles-Harmanalan coal deposits were developed in swampy and fluvial-lacustrine environments in western Anatolia under the E–W-trending graben zone during the Neogene. The present study aimed to determine the mineralogical and geochemical properties of clays interlayering the coal seams to define the origin of clay minerals, in particular, smectite. These deposits, comprising argillaceous sediment, marl, coal seam, mudstone, organic-rich shale, and sandstone, were deposited in a lacustrine environment accompanied by volcanogenic materials. The characteristics of sediments and their parent rocks were examined using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, palynology, and chemical analyses. The association of abundant smectite with quartz, amphibole, accessory chlorite, and a decrease in feldspar in fluvial-lacustrine sediments compared to those in the smectite accompanied by feldspar and volcanic glass and the absence of quartz and amphibole in the pyroclastic units suggest that smectite had detrital and authigenic origins. Flaky smectite shows either detrital, irregularly outlined coating and filling pores of terrigenous sediments or in situ precipitation edging resorbed feldspar and devitrified volcanic glass. Chemical analyses of the smectite-rich fraction show montmorillonite compositions with an average structural formula of: (Ca0.42Na0.25K0.08)(Al2.76Fe0.47Mg0.59Ti0.07Mn0.002)(Si7.65Al0.35)O20(OH)4. The positive correlation of Al2O3 vs. TiO2 and K2O vs. Rb may be related to the abundant detrital input. Feldspar and biotite were replaced by illite during diagenesis. An increase in the Ni/Co and V/(V + Ni) ratios in the altered units also suggest oxic, suboxic to anoxic conditions, under the control of a dry, warm to subtropical climate in fresh water and lakes during the Late Eocene to Middle Miocene. The slight enrichment of light rare earth elements (LREE) compared to heavy rare earth elements (HREE) with positive Eu and positive/negative Ce anomalies reflect fractional crystallization of feldspar. The δ18O and δD values of smectite and illite fractions and the wide range of δ34S isotope values (–1.5 to 15‰) for pyrite and chalcopyrite associated with coal indicate a signature of both diagenetic and partial hydrothermal origin. [ABSTRACT FROM AUTHOR]

Clay minerals are widely distributed on the surface of Earth, Mars, and Ceres in the solar systems. Among numerous clay minerals, smectites can record the history of the environment through the exchange of interlayer cations with those in water or through redox reactions with the atmosphere. Therefore, characterization of chemical compositions and crystal structures of smectites is crucial for revealing the paleoenvironment. For instance, the crystal structure within octahedral sheets of iron-bearing smectites changes to trioctahedral sheets under reduced or dioctahedral sheets under oxidizing conditions. Orbital infrared and X‑ray diffraction (XRD) analyses by Mars orbiters/rovers revealed the presence of (Fe,Mg)-smectites on the surface of Mars; however, it has been difficult to characterize the properties of these (Fe,Mg)-smectites, which are rare on the surface of Earth. In this study, we synthesized ferrian (ferric ion-rich) and ferrous (ferrous ion-rich) (Fe,Mg)-saponite and revealed the effect of valence states and iron contents on the crystal structures. These saponites were synthesized using a hydrothermal method under reduced conditions. The crystal structures and valence states of iron were analyzed by XRD, Fourier-transform infrared spectroscopy, transmission electron microscopy, Mössbauer spectroscopy, and X‑ray absorption near edge measurements. The synthesized clays were trioctahedral swelling clays and were identified as saponites. The valence state of iron in these synthesized saponites is altered by oxygen and a reducing agent in water; however, the trioctahedral structures are maintained under both oxidizing and reduced conditions, following a reversible reaction. This mechanism can be interpreted by the desorption and adsorption of hydrogen in the hydroxyls of the octahedral sheets of the smectite layers. The maximum basal spacing of the (02l) lattice plane in the octahedral sheets was defined by compiling various smectite data. When the basal spacing of (02l) is larger than the maximum in dioctahedral smectites, smectite can be identified as trioctahedral smectite. The redox state of iron in the octahedral sheet cannot be determined from the basal spacing of (02l). We revealed that the iron content in the trioctahedral sheet has a linear relationship with lattice parameter b. This provides a method to estimate the iron content in saponite from XRD data. The XRD profiles of smectites found at the Yellowknife Bay on Mars can be explained only by trioctahedral smectites, and the iron content in the octahedral sheet is roughly estimated to be 0.5–1.7 in a half-unit cell. These results indicate that the presence of (Fe,Mg)-saponite implies a reduced environment during the formation and that this iron-bearing saponite has both oxidation and reduction capabilities depending on the environment. [ABSTRACT FROM AUTHOR]

A calcium bentonite clay from Boane region (Mozambique) was subjected to an Na2CO3 activation process. The methylene blue test together with energy-dispersive X-ray spectroscopy (EDX) analysis indicated the successful ion exchange of Ca2+ by Na+ ions since the cation exchange capacity (CEC) increased from 67.5 to 74 meq/100 g and the Na/Ca ratio from 2.91 up to 15.8, as the concentration of Na2CO3, activation temperature, and activation time were varied from 2 to 6 wt.%, from 25 to 65 °C, and from 2 to 4 h, respectively. However, the increase in the CEC did not follow the same trend as the increase in the Na/Ca ratio, and for the case of Na2CO3 concentration, the increase in the CEC was limited. The X-ray diffraction (XRD) patterns also confirmed that Ca-rich bentonite was effectively modified into Na-bentonite since after the activation, the d(001) decreased from 1.52 nm to 1.30 nm. The statistical design of the experiments showed that as well as the time and the temperature × time linear interactive effect, all the other independent factors and their interactive effects had a significant influence on the CEC. The response surface methodology (RSM) indicated that higher values of the CEC can be obtained under the optimal activation conditions of 4 wt.% Na2CO3, at a temperature of 45 °C, and with an activation time of 3 h. A statistical model was used to predict the CEC, and the R2 value was 0.99529, which denotes a satisfactory result in predicting the CEC. [ABSTRACT FROM AUTHOR]

Atmospheric mineral dust is derived from arid/semi-arid region, undergoes long-range transport, and can impact surface biogeochemical processes in the pristine marine region. This study reports fluxes of mineral dust (wet and dry deposition), their clay mineralogy, and associated seasonal variability over the Northeastern Arabian Sea. Dust sources are assessed using mineral composition and their ratios as well as satellite retrievals during 2012–2015. The average wet deposition flux (293 mg m−2 day−1) of mineral dust is three times higher than dry deposition flux (96 mg m−2 day−1). A clear distinction is observed in the mineral composition of wet and dry deposited dust with smectite and palygorskite being dominant during the wet period and illite and chlorite being dominant during the dry period. Mineralogical composition and their ratios indicate that major dust sources to the Northeastern Arabian Sea are from northeast Africa, Arabian Peninsula, and southwest Asia. These observations are corroborated with the satellite retrievals, aerosol optical depth, and back trajectory analyses. [ABSTRACT FROM AUTHOR]

Lithofacies belonging to mud-flat and palustrine deposits (lake margin) in the Miocene of the Madrid Basin (Spain) have been studied. Four lithofacies corresponding to mud flat (1 and 3) and palustrine (2 and 4) deposits have been differentiated. Units 1 and 3 consist mainly of mudstones and carbonates (calcretes and diolocretes). The clay fraction is dominated by trioctahedral smectite (up to 79%) with illite and kaolinite as minor components. The d(060) spacing value shows reflections at 1.52 and 1.50 Å indicating also the presence of dioctahedral phyllosilicates. Unit 2 consists predominantly of lutites (claystones), locally with carbonate and chert nodules. The clay fraction is dominated by sepiolite (up to 96%) with variable contents of smectite and subordinate illite. The d(060) spacing value shows reflections at 1.51 and 1.52 Å indicating trioctahedral clay minerals. Unit 4 consists mostly of carbonates (limestones) with mudstone and lutite inserts. The clay fraction shows different contents of sepiolite, palygorskite and dioctahedral smectite. The analysis of a selection of trace elements (Cr, Co, Th, La, Sc) has allowed us to determine the characteristics of the source area as dioritic, somewhat different from those of the nearby materials from the Batallones sector. Sepiolite shows FWHM values ranging between 0.68 and 1.10 (2θ), indicating "low crystallinity sepiolite". Differences in the conditions of formation of magnesian smectite and palygorskite have been observed in the mud-flat and palustrine deposits. The formation of sepiolite mainly by neoformation in palustrine deposits with different hydrochemistry is remarkable, leading to differences in fibre size and crystallinity of the fibrous clay mineral. Authigenic transformation processes from previous Al-rich phases would be responsible for the formation of saponite and palygorskite in mud flat and palustrine environments, with different pH conditions. [ABSTRACT FROM AUTHOR]

Exploring the sensitivity of reservoir is the foundation of oil and gas exploration and exploitation. The damage degree of water sensitivity is affected by the clay mineral content and microscopic pore throat structure of the illite/smectite mixed layer. This study proposed a method for reservoir characterization based on digital core technology to reveal the influence of clay mineral content and micropore structure on the production of the illite/smectite mixed layer. The micropore throat characteristic parameters of the reservoir were obtained by using high-resolution micro computed tomography technology. The mineral quantitative analysis technology was used to determine the clay mineral content of the illite/smectite mixed layer. The distribution characteristics, pore radius distribution characteristics, throat length distribution characteristics, shape factor, and coordination number of the clay minerals of the illite/smectite mixed layer of the glutenite reservoir were analyzed. With the Upper Wuerhe Formation in Mahu Depression as an example, the accuracy of the proposed evaluation method was verified on the basis of the production data. Results show that the clay mineral content in the illite/smectite mixed layer and the increase in production are negatively correlated. The output of the area with the clay mineral content less than 30% in the illite/smectite mixed layer gradually increases. High-quality reservoir has the following microscopic pore throat characteristics: the distribution frequency of coordination number 5 exceeds 0.12, the average pore radius is greater than 6.34 µm, and the average throat length is greater than 8.58 µm. This study provides new technical methods and study ideas for understanding the sensitivity characteristics of glutenite reservoirs. [ABSTRACT FROM AUTHOR]

In the last decades, clays have been used in sectors such as health and cosmetics. This requires products that are increasingly pure and present homogeneous properties, hardly found in natural clays. The use of synthetic clays can be a solution. For this, it is necessary to explore techniques for their production. The main focus of this study was to synthesize a smectite clay in a simple, fast and economic way at low temperature and pressure, called static and dynamic methods. To regulate the pH of the reaction and bring it closer to the ideal synthesis conditions, two different acids were used: nitric acid (the most widely used in the literature) and hydrochloric acid (more accessible and cheaper). The results showed characteristics of uniform crystalline material with a porous structure similar to that of the smectite group. Small particle sizes of approximately 100 nm were observed by scanning electron microscopy. Stevensite clay was obtained by both synthesis methods using two different acids; the static method with hydrochloric acid stood out. The greater practicality in its development provides a more viable option for large-scale industrial production. [ABSTRACT FROM AUTHOR]

Analyses of clay minerals within the Early Cretaceous Weald Basin, Southeast England reveal kaolinite, illite and chlorite as the main detrital clay minerals while glauconite and smectite are subordinates. A kaolinite-rich assemblage which characterized the sand-dominated Ashdown and Tunbridge Wells Sand formations and an illite-dominated assemblage associated mostly with the Wadhurst Clay and Weald Clay formations are recognized. Kaolinite was enriched in the Ashdown and Tunbridge Wells Sand formations during warm and humid climate with high precipitation that encouraged chemical weathering and leaching, while cold and dry conditions favoured the concentration of illite in the Wadhurst Clay and Weald Clay formations. Rainfall patterns associated with warm climate were drastically reduced during the drier climatic conditions. Most clay minerals are detrital in origin, with chlorite being more prominent than previously recognized. Contrary to previous studies and assumptions, this study revealed that authigenic clay minerals are present in the Hastings Beds, with vermiform and mica-replacive kaolinite being the most common, consistent with humid depositional environments. Isolated authigenic illite is also present, along with a chloritized grain, providing evidence for mesodiagenesis. The absence of dickite and occurrence of kaolinite, suggest that authigenic illite formed in relatively shallow burial conditions, indicating a maximum burial depth of 2500 m–3000 m, about 1000 m deeper than previous estimates of 1500 m–2000 m. Authigenic clay minerals are absent in the Weald Clay Formation possibly because of hindered flow of meteoric water and limited growth space for authigenic minerals. This study is significant in: 1) reinforcing multiple methods to facilitate a robust and balanced knowledge of formation and transformation of clay minerals; 2) investigating detrital and authigenic clay mineral assemblages when assessing the palaeoenvironments of sedimentary basins. [ABSTRACT FROM AUTHOR]

The hydro-swelling of smectite clay minerals in low-permeability reservoirs further decreases the reservoir permeability and results in low oil recovery. Currently, the traditional chemical anti-swelling agents are widely used, but most of them are only effective in the short term and are not environmentally friendly. Here, we report the use of Fe(III) reducing microorganisms (FeRM) as a novel green anti-swelling agent to enhance oil recovery from low-permeability reservoirs. The results showed that FeRM (Proteus hauserifective) inhibited/reduced the hydro-swelling of smectite clay minerals through a three-step biochemical mineralization reaction process. The structural Fe(III) reduction in minerals by FeRM can be an important driving force for illitization. The maximum inhibition efficiency (36.6%) and shrinkage efficiency (69.3%) were achieved at 35 °C and 0.1 Mpa. Furthermore, core displacement tests showed that FeRM reduced the waterflooding injection pressure by 61.1%, increased the core permeability by 49.6%, and increased the oil recovery by 8.1%. Finally, the mechanism of FeRM-enhanced oil recovery was revealed. This study demonstrates that using FeRM to inhibit/reduce the hydro-swelling of clay minerals holds great potential to enhance the oil recovery from low-permeability reservoirs. [ABSTRACT FROM AUTHOR]