Polarizing microscope, electron microprobe and X-ray diffraction examination of minerals in a soil profile developed on a glauconite sand indicate that destabilization of glauconite can be a progressive process which appears to be the reverse of glauconitization. Glauconite in these soils appears to be destabilized into a mixed-layer glauconite-nontronite phase, which crystallizes as a plasma mineral. This material in turn is transformed into smectite+kaolinite+oxides. Loss of K and Fe is evident in whole rock as well as microprobe analyses of the samples. Thus glauconite can lose both Fe and K to aqueous solution during weathering, leaving aluminous clay minerals in the soil.

A series of V-doped titania-pillared clay catalysts, characterized by ICP-AES chemical analysis, X-ray diffraction, BET surface area measurement, and ESR spectroscopy, have been tested in the selective catalytic reduction of NO by NH3. An ESR analysis shows that V dopant is anchored to the titania pillars. Vanadyl species with differing degrees of in-plane V-O π-covalent bonding are produced depending on the method of sample preparation. Polymeric V species appear as the V content is increased. Catalytic performance of these systems depends on the method of preparation and on the V content. The best catalyst, converting 90-100% NO in the temperature range 523-623 K, is obtained by exchange of pillared montmorillonite with vanadyl ions, at an extent of exchange below the level where significant amounts of polymeric V species appear. The co-pillared catalyst, containing vanadyl centres characterized by a higher degree of in-plane ncovalent bonding (according to ESR), is less selective than the exchanged samples.

Emphasis is placed on the advantages of combining simultaneous thermal analysis methods (TG-DTA-DTG) with other complementary physico-chemical techniques for investigating synthesis and various properties of zeolites belonging to the pentasil family. TG and DTA give quantitative information on the dehydration and decomposition of organic guest molecules that interact with intermediate phases obtained during hydrothermal transformation of amorphous aluminosilicate gels into crystalline zeolites. In particular, weight losses (TG) and heat effects (DTA) due to the oxidative decomposition of tetrapropylammonium ions occluded in an intermediate phase have been related to the amount of zeolite ZSM-5 present. As a result, very small particles of this zeolite, amorphous to X-rays, could be detected in the early stages of the crystallization process. Isothermal sorption of small hydrocarbon molecules (n-hexane, 3-methyl-pentane) is used to probe the intracrystalline pore volume of zeolite ZSM-5. The total hydrocarbon uptake (TG) and the shape of the corresponding DTA peak are sensitive to steric modifications of the ZSM-5 channel system by various chemicals, while the sorption rates are better correlated to the extent of zeolite surface poisoning by boron or carbon. TG-DTA data provide an easy means of describing the filling and packing of n-hexane in ZSM-5 pore structure. Various steps characterizing isothermal competitive sorptions (nitrogen, ethylene, water) or catalytic conversions at high temperature (ethylene, methanol) over H-ZSM-5 are described. Finally, the progressive formation (removal) of carbonaceous residues resulting from these transformations are related to the actual rate of de-activation (re-activation) of a zeolitic material. In this respect, three different synthetic zeolites, namely mordenite, offretite and H-ZSM-5, which differ by their shape-selective properties and structure of their channel network, are investigated by TG.

Precise measurement of the content and the layer charge of illite and smectite is an important aspect of the mineralogical calibration of geophysical well logs and of the evaluation of mechanical and chemical properties of sedimentary rocks. Ate chnique for obtaining such measurements was developed during mineralogical studies of the Miocene clastic rocks from the Carpathian Foredeep. X-ray diffraction (XRD), chemical, cation exchange capacity (CEC), H2O sorption, and ethylene glycol monoethyl ether (EGME) sorption data were obtained for 65 samples of sandstones, shales and carbonates. The illite + smectite sum, involving all detected 2:1 minerals (smectite, illite-smectite, illite, glauconite and muscovite) was measured by XRD. The content of the illitic component was evaluated separately using % K2O and accounting for % K2O in K-feldspar. The content of the smectitic component was estimated from EGME retention using the reference data for a smectite standard, and from CEC assuming the smectitic layer charge of 0.41/O10(OH)2 (Środoń et al., in press). All these measurements produced very consistent results.

A decade of research on clays that kill human pathogens, including antibiotic-resistant strains such as methicillin-resistant S. aureus (MRSA), has documented their common characteristics. Worldwide, ∼5% of clays tested to date are antibacterial when hydrated. Most antibacterial clays are from hydrothermally altered volcanics, where volcanogenic fluids produce minerals containing reduced metals. Ferruginous illite-smectite (I-S) is the most common clay mineral, although kaolins dominate some samples. Antibacterial clay mineral assemblages may contain other reduced Fe minerals (e.g. pyrite) that drive production of reactive oxygen species (H2O2, •OH, •O2−) and cause damage to cell membranes and intracellular proteins. Ion exchange can also cause loss of bacterial membrane-bound Ca2+, Mg2+ and PO43–.

Critically important is the role of clays in buffering the hydration water pH to conditions where Al and Fe are soluble. A nanometric particle size (<200 nm) is characteristic of antibacterial clays and may be a feature that promotes dissolution. Clay interlayers or the lumen of tubular clays may absorb reduced transition metals, protecting them from oxidation. When the clays are mixed with deionized water for medicinal applications, these metals are released and oxidized.

Different antibacterial clays exhibit different modes of action. The minerals may be a source of toxins, or by adsorption may deprive bacteria of essential nutrients. In the field, the pH and Eh (oxidation state) of the hydrated clay may help to identify potential antibacterial clays. If the pH is circum-neutral, toxic metals are not soluble. However, at pH < 5 or >9 many metals are soluble and the oxidation of transition metals increases the Eh of the suspension to >400 mV, leading to bacterial oxidation.

Understanding the antibacterial mechanism of natural clay may lead to design of new treatments for antibiotic-resistant bacteria, with potential applications in wound dressings, medical implants ( joint replacements, catheters), animal feed stocks, agricultural pathogens, and production of antibacterial building materials. This research exemplifies how ‘geomimicry’ (copying geochemical processes) may open new frontiers in science.

Smectites in the montmorillonite-beidellite pseudo-binary system were synthesized from glass at the hydrothermal conditions 100 MPa and 250–500°C. Products were analysed by X-ray powder diffraction for randomly oriented and glycolated samples, and also according to the Greene-Kelly test. A new mixed-layer mineral consisting of regularly interstratified montmorillonite-beidellite was found below 400°C for M50B50 composition, where M and B denote the compositions of ideal Na-montmorillonite and Na-beidellite, respectively. Montmorillonite was obtained as a single phase below 375°C in the composition range from M100B0 to M78B22. Above 375°C, montmorillonite decomposed into an assemblage of beidellite, saponite and a silica mineral. Beidellite as a single phase was synthesized below 400°C for M0B100 composition. Above 450°C, Na-rectorite (regularly interstratified paragonite-beidellite), Mg-free dioctahedral smectite and/or Mg-rich trioctahedral smectite appeared together with silica minerals. These smectites showed the same swelling behaviour as that of montmorillonite. Phase relations in the montmorillonite-beidellite pseudo-binary system indicate no complete solid-solution series.

Clay minerals are ubiquitous constituents in soils on Earth, are occasionally found in meteorites, and may also occur on planetary surfaces in the presence of water. However, little is known about the fundamental Mössbauer parameters (the intrinsic isomer shift, δI, the characteristic Mössbauer temperature, θM, and the recoil-free fraction, f) that are characteristic of clay minerals and critical to the correct interpretation of the Fe3+/ΣFe ratios as well as the mineral modes. Spectra of well characterized single mineral samples at multiple temperatures may be used for the determinations of f. Hence, measurements of five-layer silicates with a range of layer types are presented here: nontronite, Fe-smectite, glauconite, annite and biotite. The spectra were fitted using three different software packages: WMOSS from Science, Engineering & Education Co. in Minnesota; Recoil, from the University of Ottawa in Canada; and two programs used at the University of Ghent in Belgium. Four different approaches to modelling line shapes were used: (1) Lorentzian; (2) pseudo-Voigt (convolution of Lorentzian and Gaussian curves); (3) quadrupole-splitting distributions (QSD); and (4) a technique that does not assume a particular line shape (subsequently referred to as ‘model-independent’). Values of δI, θM and f were determined using the method of De Grave & Van Alboom (1991).

Results show that multiple doublets are routinely required by all models to represent Fe-site occupancy, even when all the Fe atoms of the same valence are in the same site, as is the case for dioctahedral smectite, nontronite, mica and glauconite. Consistent values of centre shift (δ) and quadrupole splitting (Δ) were obtained for the two distributions of M2Fe3+ in the smectites. In glauconite, a single Fe2+ doublet was clearly resolved and gave systematic values for δ, Δ and area, but the two Fe3+ doublets were less defined. In annite, two Fe2+ and two Fe3+ doublets were modelled, while three Fe2+ and one Fe3+ doublet were used for biotite. Three different programs that use Lorentzian line shapes gave very similar results for δ, Δ and area. The two different implementations of QSD line shapes gave similar but sometimes slightly different results, and the pseudo-Voigt and model-independent fits usually fell between the ranges for Lorentzian and QSD results.

The value of δI is ~0.58 mm/s for Fe3+ and ~1.31 mm/s for Fe2+ across all models and line shapes, which is expected because the Fe3+ has an additional shielding 3d electron. Values for θM data are nearly identical for Fe3+ in nontronite and Fe-smectite (~450 K), somewhat varied for Fe3+ in glauconite and biotite (θM = ~730 K and ~615 K, respectively), and relatively distinct for Fe2+ (~350 K). Some values for θM and f could not be determined due to the non-monotonic behaviour of the fitted values for δ as a function of temperature. Values of f295 were 0.821–0.917 for Fe3+ and 0.662–0.743 for Fe2+, consistent with previous studies of the recoil-free fraction in micas and other silicates. Calculated scatter in δ, Δ, area and f values as a function of different line shapes and computer software was significantly reduced at lower temperatures. Sources of error in each of the calculated parameters are discussed.

The effects of acid activation on the chemical composition, surface area and pore structure of palygorskite from Xuyi (Jiangsu, P.R. China) were investigated systematically using X-ray fluorescence (XRF) and BET techniques. The palygorskite samples were activated with HCl, H2SO4 and H3PO4 of various concentrations at 80ºC for 4 h. The influences of acid concentration and acid type on the chemical composition, adsorption-desorption isotherms at 77 K, pore-size distribution, surface area and pore volume were studied in detail. The contents of most components of palygorskite decrease with increasing acid concentration except for Si and Ti. HCl shows a greater activation activity and its effect on the dissolution of components of palygorskite is greater than that of H2SO4 and H3PO4. It was found that 3 mol l–1 H3PO4 is a more efficient activator for increasing the number of micropores in palygorskite, whereas 12 mol l–1 HCl is more suitable for use in enhancing the number of meso- and macropores. The acid concentration and acid type have a great influence on the surface area and pore volume. HCl is the most effective at enhancing the external surface area and mesopore volume of palygorskite, whereas, H3PO4 is more suitable for use in improving the micropore surface and volume.

The empirical application of muds for therapeutic purposes is widely known. This is called pelotherapy and consists of the local or generalized application of a mixture of a solid phase and a liquid phase (peloid) for the recovery of arthro-rheumatic issues, bone-muscle traumatic damage and dermatological pathologies. During the time of mixing (maturation process) the mud is progressively colonized by thermophilic microorganisms that contribute to improvements in the peloid quality and endow the mud with organic substances. Several studies report diatoms as the main agent of thermal muds capable of producing anti-inflammatory sulphoglycolipid which renders the mud suitable for this use. The effect of the temperature is also considered important for therapeutic purposes.

Recent studies assessed physical, chemical and technological properties of some peloids in use at spa centres. Some maturation surveys have also been performed in recent years. The need for quality criteria establishment and certification of clayey products intended to be used currently is evident, especially for peloids which have therapeutic action. Consequently, this study aims at the compilation and analysis of some characteristics of peloids from the literature in order to contribute to a major database that allows the establishment of regulations and quality criteria for suitable applications of peloids.

Diverse applications of chlorite thermometry have been considered for better understanding the formation process in nature. Here, an approach which combined a semi-empirical thermometer (Inoue et al., 2009) with the method of Walshe (1986) was tested to estimate the redox conditions (log fO2) and the formation temperature, using the literature data from Niger, Rouez and St Martin and new data for chlorite which coexists with pink-coloured epidote in the Noboribetsu geothermal field. The log fO2 predicted for the former data sets were compatible with those estimated by Vidal et al. (2016), suggesting that the present approach is valid for quantifying the variations in log fO2. The Noboribetsu chlorites have lower Fe/(Fe + Mn + Mg) and greater Fe3+/ΣFe ratios than those observed in adjacent propylite rocks. The peculiar mineral assemblage and chemical composition are attributed to the formation under higher fO2 conditions and possibly low Fe concentration in the alteration fluids.

Different montmorillonites (Otay, Chambers, Marnia, Camp Berteau, Moosburg, Greek White, Wyoming bentonite were deferrated with a dithionite/citrate solution; iron sulphide by-products were eliminated with an HCl washing and citrates with an H2O2 oxidation. The smaller CEC after deferration could not be assigned to either (i) the occurrence of a positive correlation between CEC and particle sizes smaller than 0.2 µm or (ii) to the mean charge density of these sub-fractions. All sub-fractions had a heterogeneous interlayer cation density distribution.

The composition of Rhassoul clay is controversial regarding the nature of the pure-mineral clay fraction which is claimed to be stevensite rather than saponite. In this study, the raw and mineral fractions were characterized using various techniques including Fourier transform infrared spectroscopy and magic angle spinning nuclear magnetic resonance (MAS NMR). The isolated fine clay mineral fraction contained a larger amount of Al (>1 wt.%) than that reported for other stevensite occurrences. The 27Al MAS NMR technique confirmed that the mineral is stevensite in which the Al is equally split between the tetrahedral and octahedral coordination sites. The 29Si NMR spectrum showed a single unresolved resonance indicating little or no short-range ordering of silicon. The chemical composition of the stevensite from Jbel Rhassoul was determined to be ((Na0.25K0.20)(Mg5.04Al0.37Fe0.20☐0.21)5.61(Si7.76Al0.24)8O20(OH)4). This formula differs from previous compositions described from this locality and shows it to be an Al-bearing lacustrine clay mineral.

The nature, crystallochemistry, organization and surface properties of soil clays derived from the most representative sedimentary formations of France are described, using qualitative and quantitative mineralogical methods and high resolution transmission microscopy (HRTEM). The main results show that soil clays differ significantly from reference clays. Even when 2:1 phyllosilicates are dominant, the clays always contain multimineral phases. The smectitic component is dioctahedral and of beidellite type. Soil clay organization is specific: all the clay particles have a short lateral extension and few layers (mean 5 layers, and even mono-layers occur). The superposition of such small particles leads to the formation of what are called “texturally interstratified minerals” which are dominant in soil clays. Exchange and surface properties (high ratio of external surface to total surface area), are related to clay organization.

This study uses transmission electron microscopy (TEM) and analytical electron microscopy (AEM) supported by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the mineralogical and textural changes produced in carbonated clays by firing. Sample bars were prepared using raw clays composed of quartz, illite and carbonates with minor amounts of smectite, chlorite, feldspars and Fe oxides. The raw samples were then fired at temperatures of between 800 and 1050°C. The XRD data show that increases in firing temperature result in dehydroxylation of clay minerals, carbonate decomposition and the formation of Ca-bearing silicates (e.g. gehlenite, wollastonite, pyroxenes and anorthite). The sizes of the Ca-silicate crystals make the use of the SEM inappropriate since they lie below the resolution threshold. However, TEM/AEM do provide the required textural and compositional characterization, revealing that there is a broad range of pyroxene compositions, some of which resemble fassaite, and that Ca/Mg ratios increase with temperature. The TEM also shows significant dehydroxylation and vitrification of the clay-rich matrix at T of ~800°C. Observed mineralogical and textural changes probably occurred in a system with a local disequilibrium much like small-scale, high-temperature metamorphic reactions (i.e. pyrometamorphism). The importance of these results is that they enable the selection of more appropriate raw clay composition and firing dynamics (temperature, firing duration and cooling rate) for both the brickmaking industry and brick conservation in the field of cultural heritage.

For the purpose of clay examination, a new one-step method for the removal of organic matter was developed using sodium peroxodisulphate combined with different buffers such as sodium hydrogen carbonate, disodium hydrogen phosphate and disodium tetraborate. From an early Cretaceous black shale from the Apennines with a high organic carbon content, the <2 µm clay fraction was separated and contained 10.9 wt% organic carbon. To prevent decomposition of the clay layers, the period of oxidation was short (25-60 min) and the pH was kept between 5 and 9.5. Up to 98% of carbon was removed by this method.

It has been known for some time that when a gel of montmorillonite is freeze-dried the residual clay retains the volume and shape of the gel, and forms a skeleton of low density and some rigidity. Because there is no apparent change in the gel structure during freeze-drying, the dry residues have been studied in the past in an effort to determine the structure of the gels. However, X-ray diffraction measurements have shown that, as a result of freeze-drying, the distance between the elementary layers of Na-montmorillonite drops from high spacings (>30 Å) to zero. The present investigation demonstrates that the main reduction in interlayer spacing takes place on freezing, with a further small collapse on drying. Na-montmorillonite gels, swollen oriented aggregates of Na-montmorillonite and Na-nontronite, and swollen single crystals of Li-vermiculite and butylammonium-vermiculite, all behave in the above manner.

The adsorption of aniline (ANL) and p-chloroaniline (PCA) from 0·02 M methanol and chloroform solution on air-dried montmorillonite is determined by the conjunction of several factors: (i) basicity of the solute, (ii) complexing ability, Brönsted and Lewis acidity of the exchangeable cation, (iii) polarity and Lewis basicity of the solvent. The principal adsorption mechanisms, inferred from infrared data, are direct or indirect coordination and protonation of the adsorbate. They take place simultaneously and to a relative extent depending mainly on the exchange cation.

On Fe-, Al- and H(Al)-montmorillonite ANL and PCA give rise to type II complexes, characterised by an intense charge-transfer band in the infrared region and by the formation of radical cations, evidenced by ESR spectroscopy. This oxidation process occurs on heating in air, but with Fe3+ in vacuo also and even at ambient temperature in methanol solution. On Cu-montmorillonite ANL, contrary to PCA, does not give a type II complex; however, radical species are produced in air and in vacuo and their production is enhanced by heating.

Dissolution in HCl of hematite particles with different morphologies led to sigmoidal dissolution vs. time curves. The rate of dissolution was directly proportional to the sample surface area and independent of crystal morphology. Hematites produced by heating goethite at 600 or 800~ dissolved more rapidly per unit area than did hematites grown from solution. TEM showed that some platy crystals developed central holes after prolonged acid attack; the hole formation was attributed to enhanced dissolution at screw dislocations present on the (001) faces of the crystals. Except where particularly susceptible regions involving strained areas or dislocations were present, there appeared to be no preferential acid attack at any particular crystal face. The original morphology was usually maintained during the reaction.

New insights from the recent literature are summarized and new data presented concerning the formation, structure and morphology of halloysite. Halloysite formation by weathering always requires the presence of water. Where substantial drying occurs, kaolinite is formed instead. Halloysite formation is favoured by a low pH. The octahedral sheet is positively charged at pH < ∼8, whereas the tetrahedral sheet is negatively charged at pH > ∼2. The opposing sheet charge would facilitate interlayer uptake of H2O molecules. When halloysite intercalates certain polar organic molecules, additional (hkl) reflections appear in the X-ray diffraction pattern, suggesting layer re-arrangement which, however, is dissimilar to that in kaolinite. Associated oxides and oxyhydroxides of Fe and Mn may limit the growth of halloysite particles as does incorporation of Fe into the structure. Particles of different shape and Fe content may occur within a given sample of halloysite.

Mössbauer spectroscopy obtained with the sample at low temperatures and subject to large magnetic fields is discussed in terms of its use in analysing the naturally occurring polymorphs of FeOOH and the common growth precursor, ferrihydrite. Experiments on well-characterized synthetic samples provided benchmark results. A relatively simple means of quantitative analysis was used, in which sextets of Voigtian-shaped lines were summed and least-squares fitted. The results are discussed in terms of the magnetic structures of each compound.