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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]

Abstract The liquid phase of a peloid can be mineral-medicinal, marine or salt lake water. This study was designed to experimentally determine the interaction between two bentonites and one sepiolite, and seawater as well as dilutions thereof to verify the effect of salinity on instrumental texture measurements in clay-water mixtures prepared with these components. In all the clay-water mixtures tested, instrumental hardness and adhesiveness decreased with water content. For a given instrumental hardness or adhesiveness, bentonite retained more water in the mixture with distilled water than with seawater. In contrast, sepiolite retained more water in the mixture with seawater than with distilled water. These differences affected the thermal behaviour of the clay-water mixtures. Instrumental hardness and adhesiveness curves may be a suitable tool to tailor concentrated dispersions and after maturation could be used in thalassos and medical spas as peloids. Highlights • Mixed with seawater and their dilutions bentonite and sepiolite behave different. • Seawater salinity and pH control the textural behaviour of bentonite and sepiolite. • Instrumental hardness and adhesiveness curves are a suitable tool to tailor peloids. [ABSTRACT FROM AUTHOR]

The effect of the microwave-assisted acid treatment (MAT) on the structure and texture of dioctahedral (montmorillonite) and trioctahedral (saponite) smectites, kerolitic clays and sepiolites were studied by scanning electron microscopy, nitrogen adsorption, X-ray fluorescence, X-ray diffraction and Fourier transform infrared spectroscopy. This study shows that in the smectite group of minerals the effectiveness of MAT is notably influenced by the chemical composition of the octahedral sheet, whereas in kerolitic clays it is influenced by the proportion of the expandable phase in the mixed layer sequence. On the other hand, the reactivity of sepiolites depends on the width of the natural fibres. With these treatments, extremely high specific surface area (SSA) increments are achieved in just 16 min. The SSA increments reach values up to 231 m²/g (%ΔSBET = 80) in sepiolites, 198 m²/g (%ΔSBET = 155) in Mg-smectites, and 161 m²/g (%ΔSBET = 61) in kerolitic clays. [ABSTRACT FROM AUTHOR]

In this work the adsorption capacities of methylene blue on Mg-smectite and sepiolite and its derived material obtained after acid treatment and/or the addition of Fe at its surfaces are studied. Natural smectite with high Mg-content in its octahedral sheet (Mg-smectite) displays higher adsorption capacity than the sepiolite due to the ability of Mg-smectite to expand the basal spacing to accommodate methylene blue cations between adjacent layers and the inability of sepiolite to adsorb these cations within the structural channels. The acid-activation of Mg-smectite causes a clear decrease in the adsorption capacity attributed to the partial loss of the interlayer positions by the loss of the octahedral sheet and subsequent formation of amorphous silica. Moreover, the adsorption of the Mg-smectite decreases even more when iron oxohydroxides species are incorporated in its interlayer spacing making inaccessible the interlayer active sites for the adsorption of methylene blue cations. On the contrary, the microwave-assisted acid treatment of sepiolite causes a slight increase in the adsorption capacity related with the dispersion of fibers. Nevertheless, contrary to that observed with Mg-smectite, higher increasing of adsorption capacities are obtained after the formation of new adsorption centers due to the incorporation of iron oxohydroxides species at the external surfaces of sepiolite. [ABSTRACT FROM AUTHOR]

The trace element geochemistry of sepiolite-rich beds from five lithological sections in the Neogene Madrid Basin was analysed. The samples were collected from representative deposits including alluvial fan (Vicálvaro, Cabañas de la Sagra), palustrine (Cerro de los Batallones) and mudflat (Esquivias, Magán) facies. The mineralogical composition of the samples point out the abundant content of sepiolite, commonly higher than 95%, with variable content of quartz, feldspars, calcite, palygorskite and/or Mg-smectite. The sepiolite occurs as laminated, massive and brecciated facies, often with intraclasts of similar sepiolite composition. The geochemical results indicate that all the trace elements analysed are mostly depleted with respect to the UCC standard (Upper Crust Composition), especially REE (< 0.4). The higher depletion was observed in sepiolites from mudflat facies (V and U content are an exception). Cluster analysis of geochemical data corroborates the differences between mudflat sepiolites and those from palustrine and alluvial-related facies. The normalization of REE with chondrite allows clear differentiation between the sepiolites associated with alluvial fan facies from all the remaining samples. On the other hand, the La/Sc ratio against Th/Co ratio indicates provenance from felsic rocks. High content in F (> 4000 μg/g) and low content of Li (20–180 μg/g) is remarkable, allowing to separate samples of sepiolite formed in alluvial fan environments from those of mudflat and palustrine deposits. The geochemical complexity observed in the sepiolites was closely related to the specific mechanisms of formation under different environmental conditions. [ABSTRACT FROM AUTHOR]

The characterisation of sepiolite-bearing samples from five lutite associations occurring in the Cerro de los Batallones deposit has been carried out. Based on both the composition and texture of the sepiolite, two main formation patterns for this clay mineral, transformation from saponite by dissolution–precipitation and direct precipitation from solution, is proposed. From a compositional point of view, sepiolite oscillates between typical Mg-rich sepiolite and near Al-rich sepiolite, all samples showing variable swelling with ethylene glycol (up to 0.25Å). There is a relationship between mechanism of formation and crystallinity of the sepiolite mineral. Both DRX and FTIR analyses led to differentiate between low crystallinity sepiolite (LCS) and high crystallinity sepiolite (HCS). The presence of the triplet 2.61Å, 2.58Å and 2.56Å is especially useful for HCS identification. The two types of sepiolite show slightly a different thermal behaviour. In particular, coordinated water loss at 350°C in LCS is higher than in HCS. BET surface area is high in all studied samples, reaching up to 360m2/g and 328m2/g in LCS and HCS, respectively. Differences in the microporosity and mesoporosity contribution have also been recognised. The reported dissimilarities account for differences in the technological behaviour of sepiolite clays and therefore these differences must be taken into account as they constrain industrial uses. [ABSTRACT FROM AUTHOR]

A peloid's liquid phase can be mineral, sea or salt-lake water. This study examines the interactions among three materials, two special clays (bentonite and sepiolite) and one common clay, and three chemically different mineral-medicinal waters. In all clay–water mixtures, the hardness and adhesiveness decreased with the amount of water in the mixture. For a given hardness or adhesiveness, sepiolite retained more water than the other clays, especially in the presence of sulphate-rich mineral-medicinal water (73%). In contrast, the common clay retained the least amount of water (26%), and the bentonite samples returned an intermediate value for the amount of retained water (52–53%). These differences had a strong influence on the thermal behaviour of the mixtures and, hence, should be taken into account for their use in thermotherapy applications. There were no significant differences in the instrumental texture of the clay pastes according to the predominant anion in the mineral-medicinal waters. [ABSTRACT FROM AUTHOR]

The Madrid Basin contains large and well developed deposits of Mg-clays of Miocene age. These were developed in an environment controlled by a lacustrine saline-alkaline environment with an arid or semi-arid climate, leading to large deposits of Mg-clays. This paper summarizes the study about the formation of Mg-clay minerals in the transition from mudflat lithofacies made-up of Mg-smectite to palustrine lithofacies where sepiolite is predominant. The samples collected in the field were characterized by XRD (X-Ray Diffaction) (bulk sample and clay fraction), examined using SEM (Scanning Electron Microscopy) and analyzed by XRF (X-Ray Fluorescence) and FTIR (Fourier Transform Infrared Spectroscopy). The results suggest that during the formation of these materials dissolution-precipitation, direct precipitation and recrystallization mechanisms intervened. The type of water present (runoff, lake and/or groundwater) is a key factor for the development of the different mineral phases. In the case of the study, the analyzed series goes from mudflat conditions with influence of runoff water to a palustrine environment. During this evolution, the influence of groundwater increases with time. This is reflected in the affinity between the samples analyzed and the presence of certain elements that could serve as indicators of changes between different media. [ABSTRACT FROM AUTHOR]

Abstract: δ18O–δD measurements were made on sepiolite and associated saponite and kerolite–stevensite mixed-layers from Miocene sediments of the Madrid Basin in Spain to evaluate the relative impact of the isotopic composition of the interacting fluids and the crystallization temperature on these minerals in specific continental crystallization environments such as alluvial, palustrine and mudflat areas. Preliminary experiments of progressive heating of pure sepiolite and saponite under vacuum allowed to set a pretreatment at 200°C to remove the non-bonded water of both sepiolite and smectite before analysis of the structural oxygen and hydrogen. In combining crystallization temperatures of the different Mg-clays with potential isotopic compositions of the interacting fluids, it can be stated that the studied clay minerals precipitated during sedimentation in connection with various fluids of meteoric origin for saponite and stevensite, and with an evaporated, more saline water for sepiolite. The calculated crystallization temperatures ranged from as low as 7±5 to 35±5°C for sepiolite and from about 22±5 to 48±5°C for saponite. In the case of the kerolite–stevensite mixed-layer, it is likely that the stevensite domains crystallized first at a calculated temperature of about 10±5°C being progressively replaced by kerolite domains at a significantly higher temperature towards 55±5°C. The calculated crystallization temperature of sepiolite appears also to increase from palustrine, mudflat, mudflat/palustrine, to alluvial environments. The increasing trend goes from palustrine sepiolite formed at as low as 7±5°C from a parent water that interacted also with saponite, to sepiolite crystallized from evaporated waters at higher temperatures in mudflat/palustrine and alluvial facies. If such mineral formation occurred quasi-continuously rather than episodically, sepiolite (and saponite) formed at any given locality over a range of temperatures from waters with varied isotopic compositions. Any given Mg-mineral might then result from a mixture of crystals with different isotopic compositions consisting of end-members that interacted with the initial parental water of the smectite (δ18O=−7.25 and δD=−48‰) at low temperature of about 10±5°C, and evaporated water (δ18O=−4.00 and δD=−32‰) at temperatures up to 40±5°C. [Copyright &y& Elsevier]