In order to understand the microscopic properties of alkylammonium-intercalated vermiculites, molecular dynamics simulations employing the clayff-CVFF force field were performed to obtain the interlayer structures and dynamics. The layering behavior of alkyl chains was uncovered. With the model used in the present study (1.2 e per unit cell), the alkyl chains formed monolayers with carbon-chain lengths of C6, bilayers from C7 to C10, and pseudo-trimolecular layers from C15 to C18. Intermediate states also existed between bilayer and pseudo-trimolecular layer states from C11 to C14. The ammonium groups had two locations: most ammonium groups were located over the six-member rings (~90%), and the rest above the substitution sites (~10%). The ammonium groups interacted with the vermiculite surface through H bonds between ammonium H atoms and surface O atoms. The ammonium groups were fixed firmly on surfaces and, therefore, had very low mobility. The alkyl chains were slightly more mobile. The similarities and differences between alkylammonium-intercalated vermiculites and smectites were revealed. The layering behaviors of alkyl chains were similar in alkylammonium-intercalated vermiculites and smectites: the alkyl chain behavior was controlled by both the amount of layer charge and the carbon chain length. The distributions of ammonium groups, however, were different, caused by the layer-charge distribution in vermiculites being different from that in smectites. The atomic-level results derived in the present study will be useful for future research into and the applications of organo-vermiculites.

Amino acids are ubiquitous in the Earth’s surface environments as reactive biological molecules produced by every living thing including bacteria. To evaluate the effects of amino acids on mineral dissolution and to reveal the mechanism by which they interact with the mineral surface, we performed dissolution experiments of X-ray amorphous silica in solution containing 0.1 mmol Na with 10.0 mmol amino acids such as cysteine, asparagine, serine, tryptophan, alanine, threonine, histidine, lysine and arginine in near-neutral solutions. Dissolution experiments in solutions of 0.1, 1.0 and 10.0 mmol NaCl without amino acids were also conducted as amino acid-free controls. The results of this study indicate that basic amino acids such as histidine, lysine and arginine can interact more strongly with the negatively charged surface of amorphous silica than other non-basic amino acids due to their greater dissociation, thus forming cationic species. This electrostatical interaction enhanced dissolution rates of amorphous silica by approximately one order of magnitude compared with amino acid-free controls. In contrast, no significant effect on the dissolution rates of amorphous silica was observed in solutions containing cysteine, asparagine, serine, tryptophan, alanine and threonine because of lesser interaction with the surface of amorphous silica.

The environmental conditions and reaction paths of shallow-water glauconitization (<500 m water depth, ~15°C) close to the sediment-seawater interface are generally considered to be well understood. In contrast, the key factors controlling deep-sea glauconite formation are still poorly constrained. In the present study, green grains formed in the recent deep-sea environment of the ODP Site 959, Ivory Coast-Ghana Marginal Ridge, (~2100 m water depth, 3-6°C) were investigated by X-ray diffraction and electron microscopic methods in order to determine the rate and mechanism of glauconitization.

Green clay authigenesis at Hole 959C occurred mainly in the tests of calcareous foraminifera which provided post-depositional conditions ideal for glauconitization. Within this organic-rich microenvironment, Fe-smectite developed <10 ky after deposition of the sediments by precipitation from precursor gels containing Fe, Mg, Al, and silica. This gel formation was supported by microbial activity and cation supply from the interstitial solution by diffusion. At a later stage of early marine diagenesis (900 ky), the Fe-smectites reacted to form mixed-layer glauconite-smectite. Further down (~2500 ky), almost pure glauconite with no compositional gaps between the Fe-smectite and glauconite end members formed. This burial-related Fe-smectite-to-glauconite reaction indicates that the glauconitization process was controlled mainly by the chemistry of the interstitial solutions. The composition of the interstitial solution depends heavily on micro-environmental changes related to early diagenetic oxidation of biodegradable (marine) organic matter, microbial sulfate reduction, silicate mineral alteration, carbonate dissolution, and Fe redox reactions. The availability of Fe is suggested as the probable limiting factor for glauconitization, explaining the various states of green-grain maturity within the samples, and this cation may be the most important rate-determining element.

The rate of glauconite formation at ODP Site 959 is given by %GlSed = 22.6·log(ageSed) + 1.6 (R2 = 0.97) where %GlSed is the state of glauconitization in the sediment and ageSed is the sediment age (in ky). This glauconitization rate depends mainly on continuous cation supply (in particular Fe) and is about five times less than that in shallow-shelf regions, suggesting significantly slower reaction at the lower temperature of deep-sea environments.

The Pleistocene sediment infill of elongated glacial incisions of the southern North Sea (SNS) is often referred to as tunnel valleys (TVs). The depositional environment is not yet fully understood and the present study addresses this challenge from the perspective of clay-mineral transformation (illite to illite-smectite) reported from the largest Elsterian TV of the SNS. Material acquired from the K14-12 borehole in the Dutch offshore was analyzed by X-ray diffraction (XRD), electron microscopy, electron microprobe, and laser particle-size analysis. Illite and illite-smectite (I-S) appeared as dominant clays along with minor amounts of kaolinite, kaolinite-smectite, and chlorite. The largest amount of I-S is recognized in the main TV portion, while in pre-glacial and uppermost deposits, I-S is less abundant. The XRD peak fitting and deconvolution suggest that I-S consists of several intermediates — ordered (well crystallized illite + R3 I-S) and disordered (R0 I-S + R0 I-SS). Given the average particle sizes (>2 µm) and Kübler index values (0.415–0.341°Δ2θ), illite as well as chlorite and kaolinite were interpreted as detrital. On the basis of the distinctive distribution, grain sizes, and compositional variations of I-S, formation by means of early diagenetic in situ smectitization of illite under a cold climate is proposed. The process operated via a series of mixed-layer intermediates derived from an illite component being converted progressively to low-charged smectite. The reaction is marked by a significant net loss of K and Al with replacement by Si in a tetrahedral coordination. Layer-charge imbalance is accommodated by Fe(III) and Mg entering an octahedral sheet, whereas Ca partly fills the interlayer sites. Smectitization rates were controlled by illite grain sizes. The results of the present study support strongly the existence of an ice-marginal freshwater depositional environment at the glacial maximum in the SNS in which early diagenesis at low temperatures resulted in incomplete conversion of illite to smectite.

This study reassesses an inscribed victory catalogue from Sinope (IK Sinope 105) that is often discussed in scholarship concerning agonistic culture in the Roman world. One particularly curious element of this inscription is the empty nature of the penultimate line, which bears only the numerals rho-nu. In the existing scholarship, this is usually interpreted as the sum of all the athlete’s victories. This paper challenges the orthodox interpretation, using a combination of David French’s squeezes housed at the British Institute at Ankara, supported by autopsy and recent photographs of the stone itself. It goes on to reconsider the practice of summing athletic victories in honorific inscriptions more generally, examining a specially compiled dossier of 207 inscriptions of comparable date to IK Sinope 105, and concluding that the practice was relatively rare. Finally, this paper considers other possible interpretations of the rho-nu in IK Sinope 105, among which is the suggestion that rho-nu could be a chronographic feature. While the interpretation of the rho-nu in IK Sinope 105 remains open, the combination of a close analysis of the stone with a wider contextual consideration of the genre demonstrates how much more remains to be said about even a well-known and often cited inscription.

Clays and clay minerals dissolve over a broad pH range, such as during sediment diagenesis and in a variety of applications, including nuclear waste storage, landfills, and geopolymer binders in the construction industry. The solubility depends on process parameters (pH, temperature, pressure, etc.) and material properties (phase content, clay mineral composition, particle size, etc.). Pretreatments such as calcination or severe grinding change the material properties and could enhance solubility, which is called activation. The aim of the current study was to determine the solubility of three different clay minerals after calcination (metakaolinite, metamontmorillonite, and metaillite) in high molar alkaline solutions (NaOH) up to 10.79 mol/L and pH = 14.73. Furthermore, the solubility of an Al(OH)3 powder in alkaline solution (NaOH) was analyzed, as it can be used to adjust the Si:Al ratio of geopolymer precursors. The residues of the clay minerals after the alkaline treatment were investigated to disclose potential alterations in their phase contents. Based on the results of the thermal and alkaline activation, conclusions about the suitability as geopolymer precursors were made. All clay minerals showed an increase in solubility proportional to the concentration of the alkaline solution. The solubility decreased in the order metakaolinite > metamontmorillonite > metaillite. Thereby, dissolution was incomplete for all three clay minerals (<90%) after 7 days and congruent for metakaolinite and metaillite but incongruent for metamontmorillonite.

The properties that might influence the sequestration of aflatoxin B1 (AfB1) were examined. Laser-diffraction, particle-size analysis (LDPSA) indicated that the particle size of the smectite influences the amount of AfB1 adsorbed. Effective adsorbent smectites disperse well under combined sodium hexametaphosphate solution and ultrasonic agitation. Particle size explained 66% of the variability for most of the samples investigated in an ‘as-received’ state. One effective adsorbent smectite was especially well aggregated and required additional physical dispersion, thus raising the correlation to 73%. Transmission electron microscope (TEM) images show typical smectites and reveal the very diverse morphology of smectites in bentonites. Thin, cloud-like smectite, in TEM images, related positively to AfB1-adsorption capacity. Particles that often fold and are usually ∼0.5 µm across seem to be optimal. The selection of criteria for evaluating these smectites provides a scientific basis for their selection to obtain reliable performance. Particle size is of particular importance as outlined below, and use of LDPSA makes it possible to perform the analysis efficiently and with precision.

Corrosion of steel canisters containing buried high-level radioactive waste is a relevant issue for the long-term integrity of repositories. The purpose of the present study was to evaluate this issue by examining two differently corroded blocks originating from a full-scale in situ test of the FEBEX bentonite site in Switzerland. The FEBEX experiment was designed initially as a feasibility test of an engineered clay barrier system and was recently dismantled after 18 years of activity. Samples were studied by ‘spatially resolved’ and ‘bulk’ experimental methods, including Scanning Electron Microscopy, Elemental Energy Dispersive Spectroscopy (SEM-EDX), μ-Raman spectroscopy, X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and 57Fe Mössbauer spectrometry, with a focus on Fe-bearing phases. In one of the blocks, corrosion of the steel liner led to diffusion of Fe into the bentonite, resulting in the formation of large (width > 140 mm) red, orange, and blue colored halos. Goethite was identified as the main corrosion product in the red and orange zones while no excess Fe2+ (compared to the unaffected bentonite) was observed there. Excess Fe2+ was found to have diffused further into the clay (in the blue zones) but its speciation could not be unambiguously clarified. The results indicate the occurrence of newly formed octahedral Fe2+ either as Fe2+ sorbed on the clay or as structural Fe2+ inside the clay (following electron transfer from sorbed Fe2+). No other indications of clay transformation or newly formed clay phases were found. The overall pattern indicates that diffusion of Fe was initiated when oxidizing conditions were still prevailing inside the bentonite block, resulting in the accumulation of Fe3+ close to the interface (up to three times the original Fe content), and continued when reducing conditions were reached, allowing deeper diffusion of Fe2+ into the clay (inducing an increase of 10–12% of the Fe content).

The present study provides an example of the accurate identification of polytypes of trioctahedral 1:1 layered silicates from single-crystal X-ray diffraction data collected with the aid of a four-circle diffractometer equipped with an area detector. Single crystals of the mineral cronstedtite from the Nagybörzsöny gold ore deposit, northern Hungary, were studied. The chemical composition of some crystals was determined by electron probe microanalysis (EPMA). The precession-like images of the reciprocal space (RS) sections created by the diffractometer software and presented in the study were used to determine the OD (ordered-disordered) subfamilies (Bailey’s groups A, B, C, D) and particular polytypes. With one exception, all crystals studied belong to subfamily A. The rare polytype 1M, a = 5.51, b = 9.54, c = 7.33 Å, β = 104.5°, space group Cm is relatively abundant in this occurrence. Another polytype 3T, a = 5.51, c = 21.32 Å, space group P31 was also found. Both polytypes occur separately or in mixed, mostly 1M dominant crystals. Some 1M polytype crystals are twinned by order 3 reticular merohedry with a 120° rotation along the chex axis as the twin operation. A rare 1M+3T mixed crystal with 1M part twinned also contains a small amount of subfamily C. A possible presence of the most common 1T polytype of this subfamily cannot be confirmed because of overlap of the characteristic reflections with those of 3T. Several completely disordered crystals produced diffuse streaks instead of discrete characteristic reflections on the RS sections. The EPMA revealed Fe, Si, traces of Mg, Al, S, and Cl. One black crystal originally considered to be cronstedtite was identified as (111) twinned sphalerite. Some crystals of cronstedtite are covered partially by a honey-brown crust or small crystals of siderite.

The double hydroxide of Li+ and Al3+ is an anionic clay comprising positively charged metal hydroxide layers and intercalated anions. While the structure of the iono-covalently bonded metal hydroxide layer is well known, relatively less knowledge is available regarding the manner in which the anions and water molecules are packed in the interlayer region. The sulfate ion is of special interest as it can potentially intercalate in a multiplicity of orientations and grow an extended hydration sphere. The sulfate-intercalated double hydroxide was synthesized by the imbibition of Li2SO4 into both the gibbsite and bayerite forms of Al(OH)3 to obtain layered double hydroxides with the nominal formula Li2Al4(OH)12SO4·nH2O (n = 4–8). The as-prepared compounds were poorly ordered and did not yield any structural information. Temperature-induced partial dehydration yielded ordered phases of different structures in the two systems. Simulation of the powder patterns of different model structures, followed by structure refinement in both direct and reciprocal spaces, showed that the gibbsite-derived phase yielded a two-layer polytype of hexagonal symmetry (space group P63/m). The local symmetry of the sulfate ion was close to D2d with one of the C2 axes of the SO42− being nearly parallel to the c axis of the crystal. The bayerite-derived phase yielded a one-layer polytype of monoclinic symmetry (space group C2/m). The sulfate ion was oriented with its C3 axes tilted away from the stacking direction. Cooling and rehydration (relative humidity ~70%) resulted in a reversible expansion of the basal spacing due to the ingress of water molecules from the ambient humidity into the interlayer region. Hydration in both cases resulted in turbostratic disorder. The disorder in the bayerite-derived phase was a result of random intergrowth of motifs with rhombohedral and monoclinic symmetries.

Sepiolite and palygorskite are common as layers and nodules in the Neogene lacustrine sediments of the Eskişehir area. This study aims to determine their mineralogical and geochemical characteristics, plus the distribution of these economically important sepiolite and palygorskite deposits within the lacustrine environment. Using these data the research goes on to discuss the environmental conditions for their formation. Sepiolite and palygorskite layers are associated with dolomite, marlstone, and argillaceous limestone. The sepiolite nodules (meerschaum), which are former magnesite gravels, are observed in the Upper Miocene reddish-brown fluvial deposits derived from the ophiolite and its fractureinfills at the northern margin of the basin. Sepiolite and palygorskite are only sparsely associated with dolomite and accessory magnesite, quartz, feldspar, and amphibole. Sepiolite and palygorskite fibers formed as oriented platy fan, interwoven, and knitted aggregates in the absence of dolomite indicated precipitation from supersaturated solution. Sepiolite and palygorskite fibers edging dolomite crystals postdate dolomite and formed through precipitation in a vadose environment under semi-arid to arid climatic conditions. High values of Mg+Fe+Ni and enrichment of light rare earth elements (LREE) relative to middle rare earth elements (MREE) and heavy rare earth elements (HREE), Sr content, depletion of Rb+Ba and K, and negligible negative Eu anomalies all reflect the derivation from the Paleozoic metamorphic and Upper Cretaceous ophiolitic rocks. Locally, Upper Miocene to Lower Pliocene volcanic, volcanoclastic, and fluvio-lacustrine sedimentary rocks supplied the required Si, Mg, Al, and Fe for precipitation of Al-sepiolite and Mg-palygorskite with average structural formulae of Si11.91Al0.09O30Mg6.60Al0.78Fe0.13 (OH)4Na0.12K0.06(OH2)4·nH2O and Si7.74Al0.26O20Mg2.52Al1.13Fe0.38(OH)2(OH2)4Na0.32K0.14 Ca0.12·nH2O, respectively. In contrast to the layered sepiolites, the absence of Al and high Ni content in sepiolite nodules suggest formation through replacement of magnesite gravels at shallow burial in an alkal ine environment. The calculated meerschaum sepiol ite chemical formula i s: Si12.02O30Mg7.87Fe0.01(OH)4Na0.13K0.03(OH2)4·nH2O.

Kaolins and clays are important raw materials for production of supplementary cementitious materials and geopolymer precursors through thermal activation by calcination beyond dehydroxylation (DHX). Both types of clay contain different polytypes and disordered structures of kaolinite but little is known about the impact of the layer stacking of dioctahedral 1:1 layer silicates on optimum thermal activation conditions and following reactivity with alkaline solutions. The objective of the present study was to improve understanding of the impact of layer stacking in dioctahedral 1:1 layer silicates on the thermal activation by investigating the atomic structure after dehydroxylation. Heating experiments by simultaneous thermal analysis (STA) followed by characterization of the dehydroxylated materials by nuclear magnetic resonance spectroscopy (NMR) and scanning electron microscopy (SEM) together with first-principles calculations were performed. Density functional theory (DFT) was utilized for correlation of geometry-optimized structures to thermodynamic stability. The resulting volumes of unit cells were compared with data from dilatometry studies. The local structure changes were correlated with experimental results of increasing DHX temperature in the following order: disordered kaolinite, kaolinite, and dickite, whereupon dickite showed two dehydroxylation steps. Intermediate structures were found that were thermodynamically stable and partially dehydroxylated to a degree of DHX of 75% for kaolinite, 25% for disordered kaolinite, and 50% for dickite. These thermodynamically stable, partially dehydroxylated intermediates contained AlV while metakaolinite and metadickite contained only AlIV with a strongly distorted coordination shell. These results indicate strongly the necessity for characterization of the structure of dioctahedral 1:1 layer silicates in kaolins and clays as a key parameter to predict optimized calcination conditions and resulting reactivity.