Abstract Serra de Tramuntana of Mallorca is a mountain range built of a stack of thrust sheets composed mostly of Mesozoic platform carbonates, and it formed in the Oligocene and Miocene during the Alpine orogeny. Volcanic rocks, intruding the Triassic sediments, and known mostly from the bottom of the lowest thrust sheet, offer an opportunity for dating the post-sedimentary thermal history of this mountain range and for evaluating the maximum palaeotemperatures by studying the mineralogy and K–Ar dating of authigenic illite. Such a study was conducted on 16 samples from two outcrops, employing X-ray diffraction (XRD), optical microscopy, electron probe microanalysis and K–Ar dating of separated clay fractions. Illite was found in 10 samples, but only one sample was identified as pure volcanic rock, not contaminated by older detrital material. This sample yielded a K–Ar age of 133–140 Ma, which is within the experimental error for three grain-size fractions. This was confirmed by extrapolating the ages of a contaminated sample, and it is interpreted as representing the age of the maximum palaeotemperatures. These palaeotemperatures were estimated using several illite characteristics, including the Kübler Index applied to shales as below but close to the diagenesis/anchimetamorphism boundary (180–200°C). The dated pre-tectonic early Cretaceous thermal event is interpreted as recording the extremely high geothermal gradient at the end of the Mesozoic extensional phase. The maximum palaeotemperatures during the Oligocene–Miocene tectonic burial of Mallorca were not high enough to reset the Mesozoic K–Ar age of illite, thus being lower than ∼250°C, and, based on the preserved Cretaceous illite XRD characteristics, lower than 180–200°C.

Abstract This study investigates the influence of interlayer cations on the thermodynamics and sorption mechanisms of water in a reference Wyoming montmorillonite. The behaviour of the montmorillonite exchanged with monovalent cations (Li+, Na+, K+, Rb+, Cs+) or divalent cations (Mg2+, Ca2+, Ba2+) is compared. The analysis combines X-ray diffraction (XRD), water sorption isotherms at various temperatures and mid-infrared spectroscopy. Li+, Mg2+ and Ca2+ promote greater water uptake and swelling, whereas K+, Rb+ and Cs+ significantly limit these processes. The behaviour of Na+ and Ba2+ stands out, demonstrating intermediate water uptake and high swelling. Mid-infrared spectral analysis supports these observations. It is shown that a cation’s effect on water uptake and swelling correlates best with the product of its elementary charge and ionic radius rather than with other properties such as the electrostatic potential, solvation enthalpy or chemical hardness. However, differences in isotherm shapes, hysteresis between adsorption and desorption and the variation of isosteric heat with water content suggest the presence of two distinct sorption mechanisms: one involving Li+, Cs+, Mg2+, Ca2+ and Ba2+, and another involving Na+, K+ and Rb+. These findings indicate that isotherm shape and swelling alone do not directly reflect water uptake capacity. These findings thus outline that the chaotropic (structure-breaking) or kosmotropic (structure-making) nature of the cations, along with the complex interplay between cation hydration and TOT layer attraction, may explain the complex observed differences.

Abstract The use of nanoparticles in the composition of drilling fluids can improve some of their properties (e.g. thermal, mechanical, electrical and rheological) due to their small size and high surface area, which can diminish the loss of fluid to the formation, thereby increasing thermal conductivity, reducing friction and improving well stability. In this work, we investigated the rheological and static filtration properties and the thermal performance of non-aqueous drilling fluids with organo-palygorskite-containing hydrophobic alumina (Al2O3) and amphiphilic strontium nickelate (SrNiO3) nanoparticles in varying concentrations. The results indicate that the fluids with nanoparticles had greater plastic viscosity and lower filtrate volumes. With regard to thermal performance, the fluids with nanoparticles absorbed more heat when subjected to higher temperatures. However, this excess energy was more easily released upon cooling. This study demonstrates the affinity of nanoparticles with the solvent phase of a drilling fluid and how this interaction affects their properties, with a particular emphasis on amphiphilic nanoparticles, which have been shown to have better performance in non-aqueous fluids with organo-palygorskite.

Abstract Miocene lacustrine clay deposits formed in the Şile region of Türkiye rest unconformably on Cretaceous andesite, basaltic andesite, basalts and rare dacites. Factors controlling the genesis of this sequence include: (1) sediment provenance, (2) tectonic uplift and climatic regimes during syn- and post-depositional times, (3) burial diagenesis and (4) changes from surface weathering alterations (i.e. oxidation and hydrolysis reactions) in the critical zone. Clay minerals are dominated by kaolinite and illite, with their relative abundances varying in relation to the proximity of coal seams, stratigraphic sequence and in an overlying sand-rich fluvial deposit. Variations in the mineral abundances reveals cyclothem-like sequences with patterns of fining upwards (i.e. increasing clay mineral abundance) capped by thin coal seams. The Clay Mineral Alteration Index values for the Şile clay sequence indicate a slight trend of decreasing chemical weathering intensity up-section, which is consistent with regional geological data for terrain uplifting and a drying climate during the Miocene. Critical zone processes have modified the mineral and chemical assemblages, as evidenced by the appearance of iron oxides putatively formed from recent oxidation of the ferrous minerals siderite and pyrite, which are not found in the upper sections. Taken together, the evidence indicates that the clay minerals are derived from a combination of prior weathering of basement rocks, diagenesis after deposition and modern critical-zone weathering. The degree of each process is dependent on depositional history, stratigraphic position and depth below the land surface, all under the changing influences of tectonic uplift and regional climate. The Şile deposits provide an economical clay resource that could be important to the ceramics industry of Türkiye.

Abstract A celadonitic clay deposit is located ∼40 km north-west of Yazlıca-Kütahya (Türkiye) and has promising reserves for ceramic production. To evaluate the potential use of this region, 10 representative clay samples were collected and characterized using X-ray diffraction (XRD), polarized-light microscopy (PM), X-ray fluorescence (XRF), differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). According to the Chemical Index of Alteration and Chemical Index of Weathering, the celadonitic clay samples were formed by strong chemical alteration of the Kızıltepe volcanic rocks occurring in the study area. Based on XRD data, SEM-EDS data and chemical and thermal analysis results, the primary minerals present were celadonite-Al, montmorillonite and nontronite in the clay samples formed by the weathering of basaltic rocks. The clay samples were used in thermal and physical tests. Firing properties, including water absorption, dry shrinkage, firing shrinkage, total shrinkage and glaze adhesion, were determined. The white clay specimens are suitable for more decorative and less load-bearing applications, having high porosity and low strength. The green clay samples, however, are ideal for technical and industrial ceramics, having an extremely compact structure and high strength. The properties of these two clays are beneficial for application in different areas in terms of their mechanical and ceramic performance. Additionally, the representative green celadonitic clay samples were used in recipes for opaque, transparent and matte glazes, creating artistic glaze effects for pigments. Hence, the green clay samples could be used as a ceramic pigment.

Abstract A clay from Weslatiya that is widely used in Tunisian ceramic production has abundant reserves but generates significant waste, posing environmental concerns if not handled appropriately. This study explores the valorization of this local clay by incorporating ceramic waste (chamotte) and quartz sand to produce eco-friendly materials, in line with sustainability and circular economy principles. X-ray diffraction and scanning electron microscopy analyses reveal that incorporating chamotte at levels exceeding 15% by weight improves the material’s properties. The Young’s modulus of the composite increases to 80 GPa, more than 2.5 times that of the basic clay. Chamotte can replace up to 30% of quartz sand without significantly affecting densification or porosity while preserving structural integrity. This approach offers flexibility in terms of material composition, enhancing performance and promoting sustainability by reusing waste materials for high-performance ceramics in industrial applications.

Abstract Peloids are natural therapeutic muds or clays used in balneotherapy and other health treatments. The aim of this study is to prepare and qualify three artificial peloids by maturation for 360 days of some Tunisian smectitic clays with a naturally chlorinated sodic mineral water from a spring in Korbous, Tunisia. This was done to improve our understanding of the behaviour of these clays and the physicochemical changes that affect the clays during maturation, with the purpose of providing suitable raw materials as a solid phase for peloid preparation. The results showed that parameters such as mineralogy, geochemistry, granulometry, cation-exchange capacity, consistency parameters (Atterberg limits and plasticity index), specific surface area, cooling kinetics and pH are all affected by the geochemistry of the thermal water used during maturation. Mineralogical modifications mostly concern the clay minerals’ contents, particularly smectite, and subordinately the dissolution of gypsum and the neoformation of halite. The observed improvements to the plasticity index and cooling kinetics can be explained by the ability of water molecules, and especially cations, to diffuse into the clay particles. The main exchangeable cations are Na+ and Ca2+, along with Mg2+ and K+, which promote swelling and increase water retention and consequently retention of heat in thermal spa treatments. The chemical composition of the major elements is closely linked to the mineralogical compositions of the clays, and also to the chemical composition of the thermal water used in their maturation. The safety profiles of the peloids obtained at different maturation times were evaluated, particularly regarding their content of potentially toxic elements such as arsenic.