Crystalline Mineral Phases Research Articles

Role of mineralization inhibitors in the regulation of hard tissue biomineralization: relevance to initial enamel formation and maturation.

Vertebrate mineralized tissues, i.e., enamel, dentin, cementum, and bone, have unique hierarchical structures and chemical compositions. Although these tissues are similarly comprised of a crystalline calcium apatite mineral phase and a protein component, they differ with respect to crystal size and shape, level and distribution of trace mineral ions, the nature of the proteins present, and their relative proportions of mineral and protein components. Despite apparent differences, mineralized tissues are similarly derived by highly concerted extracellular processes involving matrix proteins, proteases, and mineral ion fluxes that collectively regulate the nucleation, growth and organization of forming mineral crystals. Nature, however, provides multiple ways to control the onset, rate, location, and organization of mineral deposits in developing mineralized tissues. Although our knowledge is quite limited in some of these areas, recent evidence suggests that hard tissue formation is, in part, controlled through the regulation of specific molecules that inhibit the mineralization process. This paper addresses the role of mineralization inhibitors in the regulation of biological mineralization with emphasis on the relevance of current findings to the process of amelogenesis. Mineralization inhibitors can also serve to maintain driving forces for calcium phosphate precipitation and prevent unwanted mineralization. Recent evidence shows that native phosphorylated amelogenins have the capacity to prevent mineralization through the stabilization of an amorphous calcium phosphate precursor phase, as observed in vitro and in developing teeth. Based on present findings, the authors propose that the transformation of initially formed amorphous mineral deposits to enamel crystals is an active process associated with the enzymatic processing of amelogenins. Such processing may serve to control both initial enamel crystal formation and subsequent maturation.

The effect of titanium compounds addition on the microwave dielectric properties of the ZnO–Nb2O5 ceramics for LTCC

The ZnO–Nb2O5 ceramics with titanium compounds were prepared by solid state reaction method. The effect of titanium compounds addition on the densification, phase development, microstructure and microwave dielectric properties of the ZnO–Nb2O5 ceramics was investigated. Adding TiO2 to the ZnO–Nb2O5 ceramics in different order, the X-ray diffraction patterns showed that ZnTiNb2O8 was the main crystalline phase, only the minor crystalline phases were different. The TiO2 phase could not coexist with ZnNb2O6 phase, but the CaTiO3 phase could coexist with ZnNb2O6 phase. The effect of adding TiO2 in different order on the microstructures of ZnO–Nb2O5 ceramics is unconspicuous. Compared to the ZnNb2O6–0.2CaTiO3 ceramics, it is easier to lower the sintering temperature of the ZnNb2O6–1.8TiO2 ceramics by doping BaCu(B2O5). The τf values of the ZnNb2O6–1.8TiO2 ceramics and ZnNb2O6–0.2CaTiO3 ceramics can be adjusted to zero by doping opposite τf values compounds, but the two mechanisms of adjusting τf are different.

HVOF sprayed Al–Cu–Cr quasicrystalline coatings from coarse feedstock powders

Al–Cu–Cr quasicrystalline (QC) coatings were prepared from coarse feedstock powders by a high velocity oxy-fuel (HVOF) system DJ2700. The contrast experiments were performed by low power atmospheric plasma spray (LPAPS) using the same Al65Cu20Cr15 QC powders, and by HVOF spraying Cu180 powders with the size of 44–61μm. The phase composition, microstructure and microhardness properties of the QC coatings were investigated. XRD results showed that the feedstock and coatings contained a predominant phase, icosahedral quasicrystal (IQC) I-Al65Cu24Cr11, and three minor crystalline phases: α-Al69Cu18Cr13, θ-Al13Cr2 (i.e. Al83Cu4Cr13) and ε-Al2Cu3. A qualitative analysis on the XRD patterns indicated that, a HVOF-sprayed coating contained more IQC and fewer crystalline phases in the one deposited by LPAPS. Moreover, the higher the input heat energy, the fewer IQC and the more crystalline phase the coating contained, for not only HVOF but also LPAPS. As confirmed by experimental results, when the HVOF-sprayed QC particle impacted onto the substrate surface, the unmelted solid part of particle broke up, and the previously deposited coating portion was deformed and densified and even cracked by impingement of the in-flight particles with high velocity; which minified splats and densified the as-sprayed coating. Thus, the HVOF-sprayed coatings from such coarse (61–74μm) QC powders had much smaller splats and much denser microstructures with lower porosity and higher microhardness, compared with those deposited by LPAPS using the same feedstock, although the preferential particle size of feedstock powders for HVOF spraying is conventionally 5–45μm. Furthermore, based on the contrast experimental results, the necessary and sufficient conditions for occurrence of the particle impact breakage behavior in the thermal spray process are: (1) the high brittleness of feedstock and (2) the high velocity and low melting degree of spray particles, respectively.

Development of Aluminium Oxychloride Bonded Fused Magnesia Based Basic Refractory Castable

The exclusive demand for super quality basic refractory castable in the lining of steel making furnaces for the manufacture of inclusion free steel has posed a real challenge towards its innovative development. The present study demonstrated the formation of a new generation cementless basic refractory castable using Al-oxychloride as non-conventional binder and fused magnesia as aggregate. The basic castable body showed a distinct improvement in thermomechanical properties and dense advance matrix microstructure at low, intermediate as well as high temperature. The powder XRD pattern of fused magnesia based basic castable on sintering at 1500°C revealed the existence of well crystalline periclase as major along with magnesium aluminate as minor crystalline phases. The SEM images of cement free basic castable on sintering at 1500°C exhibited an advance matrix microstructure with uniform distribution of normal size periclase grains surrounded by MgAl2O4 and Al2O3 layers at the grain boundaries with occasional presence of micro porosity.

Dependence of Soft Magnetic Properties of <inline-formula> <tex-math notation="TeX">${\rm Fe}_{81-85.5}{\rm Si}_{2}{\rm B}_{10}{\rm P}_{1.5-6}{\rm Cu}_{1}$ </tex-math></inline-formula> Alloys on P Content

Effects of P content in amorphous and nanocrystalline FeSiBPCu soft magnetic alloys were investigated by comparing the corresponding change in the saturation magnetic flux density and coercivity. Ribbons were prepared using a high induction melting and melt spinning method. As-quenched Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">85.5</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.5</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> alloy consisted of minor crystalline phase. With an increase of P content, the glass forming ability was enhanced. The decrease in the saturation magnetic flux density associated with increased P content, was mainly ascribed to the decrease in Fe content. Nanocrystalline Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">87-x</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> alloys exhibited higher saturation magnetic flux density and lower coercivity, when x was >2 at%. The best soft magnetic performance was obtained at x = 2 at%, where the saturation magnetic flux density was 1.87 T. The coercivity was decreased with P content, indicating that the size of α-Fe grains became smaller with the increase of P content.

A 31P NMR and TG/DSC-FTIR Investigation of the Influence of Initial pH on Phosphorus Recovery as Struvite

Phosphorus can be reclaimed from nutrient-rich sources as the mineral struvite (MgNH4PO4·6H2O) for reuse as fertilizer. This study determines the impact of initial pH (pHi) from 8 to 11 on the fraction of precipitated struvite from a MgCl2–(NH4)2HPO4–NaCl–H2O system. The rate of P removal from solution increases with pHi and maximizes at pHi 10. Scanning electron microscopy (SEM) of recovered precipitates shows changes in morphology and decreasing particle size with increasing pHi. 31P nuclear magnetic resonance spectroscopy (NMR) confirms that struvite constitutes 96–99% of the phosphate at pHi 8–10, with newberyite (MgHPO4·3H2O) as a minor crystalline phase. At pHi 11, 60% of the solid is struvite, with 22% of the phosphate contained in an amorphous phase and 18% as sodium phosphate. Thermogravimetric analysis (TG) reveals a correlation in the mass loss from the solids with the percentage of struvite detected. Coupling Fourier transform infrared spectroscopy (FT-IR) with TG indicates that the molar conc...

Mechanical Properties of a Lithium Disilicate Strengthened Lithium Aluminosilicate Glass‐Ceramic

A glass composition in the Li2O–Al2O3–SiO2 (LAS)‐ternary phase diagram is presented, which enables the crystallization of Li2Si2O5 as well as LiAlSi2O6 upon a well‐defined heat treatment. Li2Si2O5 is the minor crystalline phase in the glass‐ceramic and generates through the bulk strengthening of the LAS glass‐ceramic. A flexural strength as higher as 400 MPa is measured in the proposed glass‐ceramic formulation, thus outperforming conventional LAS‐glass‐ceramics. A combination of the presence of those two crystalline phases of very different mechanical properties and coefficient of thermal expansion as well as the microstructure are believed to contribute largely to the enhancement of the measured properties.

Arsenic Species Formed from Arsenopyrite Weathering along a Contamination Gradient in Circumneutral River Floodplain Soils

Arsenic is a toxic trace element, which commonly occurs as contaminant in riverine floodplains and associated wetlands affected by mining and ore processing. In this study, we investigated the solid-phase speciation of As in river floodplain soils characterized by circumneutral pH (5.7-7.1) and As concentrations of up to 40.3 g/kg caused by former mining of arsenopyrite-rich ores. Soil samples collected in the floodplain of Ogosta River (Bulgaria) were size-fractionated and subsequently analyzed using a combination of X-ray fluorescence (XRF) spectrometry, powder X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and selective chemical extraction of poorly crystalline mineral phases. Arsenic and Fe were found to be spatially correlated and both elements were strongly enriched in the fine soil particle size fractions (<2 μm and 2-50 μm). Between 14 and 82% of the total As was citrate-ascorbate extractable. Molar As/Fe ratios were as high as 0.34 in the bulk soil extracts and increased up to 0.48 in extracts of the fine particle size fractions. Arsenic K-edge XAS spectra showed the predominance of As(V) and were well fitted with a reference spectrum of As(V) adsorbed to ferrihydrite. Whereas no As(III) was detected, considerable amounts of As(-I) were present and identified as arsenopyrite originating from the mining waste. Iron K-edge XAS revealed that in addition to As(V) adsorbed to ferrihydrite, X-ray amorphous As(V)-rich hydrous ferric oxides ("As-HFO") with a reduced number of corner-sharing FeO6 octahedra relative to ferrihydrite were the dominating secondary As species in the soils. The extremely high concentrations of As in the fine particle size fractions (up to 214 g/kg) and its association with poorly crystalline Fe(III) oxyhydroxides and As-HFO phases suggest a high As mobilization potential under both oxic and anoxic conditions, as well as a high bioaccessibility of As upon ingestion, dermal contact, or inhalation by humans or animals.

Clay Mineralogy of Gelic Soils from the Fildes Peninsula, Maritime Antarctica

The general physical and chemical properties of Antarctic soils have been long studied, although detailed soil mineralogy remains comparatively little explored. The aim of this study was to characterize the clay mineralogy of soils from Fildes Peninsula, King George Island, Maritime Antarctica. The clay fraction of four soil profiles was studied by x-ray diffraction (XRD). Poorly crystalline mineral phases were sequentially treated with 0.1 mol L−1 sodium pyrophosphate, 0.2 mol L−1 ammonium oxalate, and 0.5 mol L−1 NaOH. After each extraction, differential XRD patterns were obtained. The presence of primary minerals in the clay fraction, such as K-feldspar, plagioclase, pyroxene, and mica, indicates the low degree of chemical weathering. However, ornithogenic influence leads to the phosphatization of the mineral substrate and neoformation of secondary phosphates containing Fe and Al, such as leucophosphite, metavariscite, and minyulite. Overall, what makes these Antarctic soils unique is (i) the widespread occurrence of poorly crystalline minerals in the clay fraction with concentrations ranging from 20.9 to 65.6%, (ii) their association with organic matter forming organo-metallic complexes, and (iii) Al- and Si-rich oxides (allophane and imogolite) and poorly crystalline Fe oxides. Such high amounts of poorly crystalline mineral phases can compensate for the generally low clay content, favoring the retention of ionic and polar chemical compounds, including pollutants.

The influence of TiO2 content on the properties of glass ceramics: Crystallization, microstructure and hardness

The effects of compositional variation, crystallization behavior, crystalline phases and microstructure formed in the SiO23Al2O33CaO (SAC) glass system using various amounts of TiO2 as nucleating agent were investigated by Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and Fourier transform infrared spectroscopy (FTIR) techniques. The crystallization kinetics and mechanical properties of SAC glass ceramics were studied using crystallization peak temperature (Tp) of three different glasses as obtained from DTA, the activation energy (E) and Avrami exponent (n) were also determined. The crystallization peak temperature (Tp) and activation energy (E) were found to increase with the increase in TiO2 content. The major crystalline phases were anorthite and wollastonite along with gehlenite and titanite as the minor crystalline phases present in the glass ceramic system. The studies showed that the three dimensional crystalline structure and the microhardness increased with the increase of TiO2 content in the glass ceramics system.

Thermal processing and crystallization of amorphous Mg‐Ca silicates

AbstractThe structural evolution of sol–gel‐produced amorphous Mg(x)Ca(1–x)SiO3 silicates is investigated. Mid‐IR Fourier transform infrared spectroscopy and synchrotron X‐ray diffraction are used to confirm the amorphous nature of the as‐prepared silicates, while subsequent in situ synchrotron X‐ray powder diffraction measurements are used to study the evolution of crystalline mineral phases as a function of annealing temperature. Multiple silicate phases, including diopside, enstatite, forsterite, and SiO2, are identified, while Rietveld (i.e., structure) refinement of the diffraction data is used to quantify phase change relationships. Investigated as possible analogs for the refractory dust grain materials likely to have been present in the early solar nebula, the likely relevance of these investigations to the observed silicate compositions of chondritic meteorites and cometary bodies and the processing of their precursor materials is discussed.

Observation of magnetic behavior at low temperature in the Mg2Al4Si5O18 system

• Cordierite Mg 2 Al 4 Si 5 O 18 system has been fabricated using the melt-quenched technique. • The fabricated materials showed diamagnetic behavior near room temperatures. • Below 25 K, the ferromagnetic/ferromagnetic transition was obtained. • Magnetic transition was traced to the presence of MgO and MgAl 2 O 4 (spinel) in Mg 2 Al 4 Si 5 O 18 . The Mg 2 Al 4 Si 5 O 18 materials were prepared by the melt-quenching technique using an arc-melter system. The heat treatments of the samples were performed at 1300 °C for 48 h and 72 h. From XRD analysis, while major phase in the samples was the α-cordierite, the MgAl 2 O 4 (spinel) and MgO phases were also detected. It was observed that the uniformly distributed rods are formed perpendicular to the sample surface. EDX analysis revealed that the atomic composition of the rods is Mg 2 Al 4 Si 5 O 18 . The samples exhibited diamagnetic behavior at 300 K and the magnetization increased sharply at 25 K, suggesting a ferromagnetic or ferrimagnetic transition. This type of the magnetic behavior originates from minor crystalline phases, such as MgO and MgAl 2 O 4 .

Preparation of glass–ceramic glazes for fast firing applications by CaF2 substitution with B2O3 in the CaO–CaF2–Al2O3–SiO2 system

The present work aims to obtain glass–ceramic glazes for floor tile applications. In this regard, CaF 2 was gradually replaced by B 2 O 3 in the glass compositions belonging to the CaO–CaF 2 –Al 2 O 3 –SiO 2 system. This substitution led to a noticeable decrease of crystallization peak temperatures and to an alteration of the crystallization trend. In the B 2 O 3 bearing glazes, anorthite and gehlenite were identified as the major and minor crystalline phases, respectively. During concurrent crystallization and sintering based on the fast firing program, glass–ceramic glazes containing 9 weight parts of fluorine and 12 weight parts of boron oxide showed the most desirable sinterability. The optimized glass–ceramic glazes offered acceptable micro-hardness, whiteness and thermal expansion behavior after fast firing heat treatment.

Stabilization/Solidification (S/S) Pb and W Contaminated Soils using Type I/II Portland Cement, Silica Fume Cement and Cement Kiln Dust

Stabilization/solidification (S/S) processes were utilized to immobilize lead (Pb) and tungsten (W) in contaminated soils, the inclusion of W motivated by the use of the new W-based ammunition. Artificially contaminated soils were prepared by mixing either kaolinite or montmorillonite with 10% Pb and 1% W (all percentages by dry weight). Type I/II Portland cement (PC), silica fume cement (SFC) and cement kiln dust (CKD) were used as S/S agents. The S/S agents were added at 5, 10 and 15 % for a curing time of 1-, 7- and 28-days. The toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) were used to evaluate the effectiveness of the treatments. X-ray powder diffraction (XRPD) was used to investigate the crystalline mineral phases responsible for Pb and W immobilization. The TCLP results showed that regardless of clay type and stabilizing agents, the Pb concentrations decreased with increasing pozzolan content. PC and SFC exhibited similar performance depending on the particular sample (not consistent with soil type, dosage, and curing time). The most effective stabilizing agent on Pb leachability was PC despite SFC being silica-enriched which should have contributed to its greater immobilization of Pb. TCLP-W was immobilized below 1 mg l-1 in every case. The most effective stabilizing agent on the SPLP-Pb leachability was CKD, consistently demonstrating among the lowest concentrations for each soil type due to pH control. PC and SFC exhibited similar performance depending on the particular sample (not consistent with soil type, dosage, and curing time). The W concentrations in SPLP leachate were very low in most samples indicating that W could be immobilized upon S/S processes even though W solubility is very high at elevated pH conditions (662.9 mg l-1 at pH~11), and would remain immobilized under SPLP exposure conditions. The XRPD results revealed that the formation of lead silicate (Pb4SiO6), stolzite (PbWO4) and lead tungsten oxide (Pb0.29WO3) were strongly associated with the immobilization of Pb in the S/S matrix.

Role of vermiculite and zirconium–vermiculite on the formation of zircon–cordierite nanocomposites

The Zr4+–vermiculites were studied in their new role of the zircon precursor in the clay minerals mixtures which were prepared for firing of the zircon–cordierite nanocomposites. Currently there is a lack of data available about the structure of Zr4+–vermiculites, on which this study was performed. The modeling of the arrangement of interlayer material in the Zr4+–vermiculite led to new findings that water molecules are attracted more strongly by Mg2+ cations than by Zr-tetrameric cations, and that both the tetrameric cations [Zr4(OH)14(H2O)10]2+ and [Zr4(OH)8(H2O)16]8+ may be present in the interlayer space of the Zr4+–vermiculites. Vermiculites from two different localities Czech Republic (Verm1) and from Brazil (Verm2) were intercalated using the zirconyl chloride (ZrOCl2–30% solution in HCl) and the prepared Zr4+–vermiculites were designated as Zr4+–Verm1 and Zr4+–Verm2, respectively. Influence of the Zr4+–Verm1 and Zr4+–Verm2 in the mixtures of clay minerals on the properties of zircon–cordierite nanocomposites were investigated by their comparison with the properties of the zircon–cordierite nanocomposites, which were prepared using saturation of the clay minerals mixtures containing Verm1 and Verm2 with the zirconyl chloride (ZrOCl2–30% solution in HCl). The zircon–cordierite nanocomposites fired from the clay mineral mixtures containing Zr4+–Verm1 and Zr4+–Verm2 showed a maximum porosity of P=58 and 60%, skeletal density SD=3.2 and 3.6, and the smallest pores with a median pores diameter MDP=18 and 15μm, respectively, in comparison with the zircon–cordierite nanocomposites fired from the clay mineral mixtures containing Verm1 and Verm2 and saturated with zirconyl chloride solution. The type of vermiculite Verm1 or Verm2 in the clay mineral mixtures did not affect the contents of the crystalline mineral phases in cordierite and zircon–cordierite nanocomposites.

Transient precursor amorphous phases in biomineralization.In the footsteps of Heinz A. Lowenstam

AbstractHeinz A. Lowenstam’s discovery in 1967, together with Ken Towe that the magnetite mineral in mature chiton teeth forms from a disordered transient precursor phase, ferrihydrite, remained an isolated curiosity for 30 years. During the last 15 years, many more examples were found in both invertebrates and vertebrates, where the mature crystalline mineral phase is formed through a transient amorphous precursor phase. Here we review this widespread phenomenon, and also describe the details of the transformation process in the formation of the calcitic spicules of the sea urchin larva. We identify many open questions.

The Characterization Of CaCO3 in a Geothermal Environment: A Sem/Tem-Eels Study

AbstractMineralization of microbial biomass is a common phenomenon in geothermal habitats, but knowledge of the structure of the minerals formed in these environments is limited. A combination of spectroscopic, microscopic, and stable isotopic methods, as well as the chemical analysis of spring water, were employed in the present study to characterize calcium carbonate minerals deposited in filamentous cyanobacterial mats in different locations of La Duke hot spring, a circumneutral thermal feature near the north entrance of Yellowstone National Park, Montana, USA. Calcite was the primary crystalline mineral phase associated with biofilm-containing deposits closest to the source of the spring and the suspended microbial biomass in a pool further from the source. The carbonate minerals at all sites occurred as aggregated granules, ~2 μm in diameter, in close association with the microbial biomass. Only in the deposits closest to the source were the granules organized as laminated structures interspersed with microbial biomass. The calcium carbonate grains contained two distinct regions: a dense monolithic calcite core and a porous dendritic periphery containing organic matter (OM). Electron energy loss spectroscopy (EELS) indicated that the voids were infilled with OM and carbonates. The EELS technique was employed to distinguish the source of carbon in the organic matter and carbonate mixture. The studies of carbon isotope compositions of the calcium carbonates and the saturation indices for calcite in the spring waters suggest that processes (abiotic vs. biotic) controlling the carbonate formation may vary among the sampling sites.

Organic matter content and features related to associated mineral fractions in an acid, loamy soil

Sorption of soil organic matter on mineral surfaces is now recognized as a major organic carbon (C) stabilization process. To investigate the role of organo‐mineral interactions in carbon‐rich soils, we separated organo‐mineral associations by sequential density fractionation in the top‐ and subsoil of a forest Acrisol (umbrept) from southern France. Fractions were characterized by scanning electron microscopy, X‐ray diffraction, elemental analysis, 13C NMR and δ13C. For each horizon, we isolated five types of association: light organic matter non‐occluded, and occluded in aggregates (&lt;1.9 g cm−3), and microaggregates formed by poorly crystallized mineral phases (1.9–2.2 g cm−3), by phyllosilicates (2.2–2.5 g cm−3) and by primary mineral particles weakly complexed with organic compounds (&gt;2.5 g cm−3). Carbon accumulation in organo‐mineral fractions was correlated with a relative enrichment in hydrophobic compounds (alkyl C or aromatic C). In contrast, the content in nitrogen and carboxylic groups was more constant. Poorly crystalline mineral phases stabilized the largest amount of soil organic matter. We compiled data from previous studies carried out on soils with different mineralogies (n = 20) and found a significant correlation between the δ13C and the C:N ratio of sorbed organic compounds according to the C content of fractions. This general trend is in line with the conceptual model of a zonal structure of soil organic matter sorbed on mineral surfaces. Furthermore, we hypothesized that the accumulation of hydrophilic (O‐alkyl C) and hydrophobic (alkyl C and/or aromatic C) organic compounds on mineral surfaces is favoured by the structural organization of organo‐mineral associations. The same organo‐mineral associations were found in top‐ and subsoils, indicating similar stabilization processes in surface and deeper horizons.

Speciation of Np(V) uptake by Opalinus Clay using synchrotron microbeam techniques

Synchrotron-based X-ray absorption spectroscopy has been used to determine the chemical speciation of Np sorbed on Opalinus Clay (OPA, Mont Terri, Switzerland), a natural argillaceous rock revealing a micro-scale heterogeneity. Different sorption and diffusion samples with Np(V) were prepared for spatially resolved molecular-level investigations. Thin sections of OPA contacted with Np(V) solution under aerobic and anaerobic conditions as well as a diffusion sample were analysed spatially resolved. Micro-X-ray fluorescence (μ-XRF) mapping has been used to determine the elemental distributions of Np, Fe and Ca. Regions of high Np concentration were subsequently investigated by micro-X-ray absorption fine structure spectroscopy to determine the oxidation state of Np. Further, micro-X-ray diffraction (μ-XRD) was employed to gain knowledge about reactive crystalline mineral phases in the vicinity of Np enrichments. One thin section was also analysed by electron microprobe to determine the elemental distributions of the lighter elements (especially Si and Al), which represent the main elements of OPA. The results show that in most samples, Np spots with considerable amounts of Np(IV) could be found even when the experiments were carried out in air. In some cases, almost pure Np(IV) L(III)-edge X-ray absorption near-edge structure spectra were recorded. In the case of the anaerobic sample, the μ-XRF mapping showed a clear correlation between Np and Fe, indicating that the reduction of Np(V) is caused by an iron(II)-containing mineral which could be identified by μ-XRD as pyrite. These spatially resolved investigations were complemented by extended X-ray absorption fine structure measurements of powder samples from batch experiments under aerobic and anaerobic conditions to determine the structural parameters of the near-neighbour environment of sorbed Np.

Cation migration in hydrothermal clays: The problem of mineralization criteria in gas-hydrothermal fluids of hydrothermal fields in Southern Kamchatka

Based on a comprehensive study of the hydrothermal clay layer that occurs in geothermal fields, the conditions of formation of cation composition in argillitized rocks are discussed. Under the influence of gas-water fluids and pore solutions, micro- and nano-mineral mixtures are formed in hydrothermal clays; these mixtures include crystalline, amorphous, and transitional mineral phases. A considerable role in their composition belongs to cations of several metals (Fe, Al, Ti, Na, Mg, Ca, K, Mn, and Ba), as well as Si, C, N, S, and volatiles (F− and Cl−). The sources of cations and other elements are unaltered host rocks, newly formed hydrothermal-metasomatic rocks, hydrothermal clays, salt deposits, siliceous, carbonate, and other sediments, as well as deep fluids. In the structures of geothermal anomalies and deposits the “hydrothermal metasomatic rock—gas-water fluid—newly formed mineral chemical compounds” united system is formed. Each of the elements of this system takes part in the transportation, accumulation, and redistribution of metals. This approach to studies of the geochemistry of present-day geothermal systems may serve as a foundation for developing criteria for the presence of mineralization in metasomatites, gas-hydrothermal fluids, and new mineral associations.