Search

The composition of trench sediment at convergent margins exhibits strong compositional links to the corresponding arc magmas. To test for the existence of such links at the Hikurangi margin, we provide a first geochemical characterisation of the IODP sites U1518 and U1520 drilled at the upper and incoming plate respectively. The identification of a décollement in the trench sediments allows distinction of the accreting clastic sediment above the décollement and the subducting pelagic and volcaniclastic material below it. The accreted material and that located above the décollement show homogenous Pb, Sr and Nd isotope ratios with bulk compositions of 206Pb/204Pb: 18.8953, 207Pb/204Pb: 15.6552, 208Pb/204Pb: 38.8371, 87Sr/86Sr: 0.70935, 143Nd/144Nd: 0.51241. In contrast, the material located below the décollement shows more heterogeneous Pb-Sr-Nd isotope ratios and bulk compositions of 206Pb/204Pb: 20.4826, 207Pb/204Pb: 15.7355, 208Pb/204Pb: 39.9833, 87Sr/86Sr: 0.70752, and 143Nd/144Nd: 0.51286. Tectonic erosion in the Hikurangi margin implies that accreted material could subsequently be subducted from the underside of the upper plate. Therefore, this characterisation is of prime importance for future work to constrain the role that subducted materials play in the compositional variations of the arc magmatism associated with subduction along the Hikurangi margin. [ABSTRACT FROM AUTHOR]

Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47.4–49.0 wt.% SiO2, 13.4–14.9 wt.% Al2O3 and 10.7–14.1 wt.% FeOT. These compositions are lower in FeOT and higher in SiO2 than previous estimates and have distinct La/SmN and Dy/YbN ratios that link them to the lowermost volcanic succession (Milne Land Formation) of the regional East Greenland flood basalt province. New major- and trace element compositions for the FG-1 dyke swarm, previously taken to represent Skaergaard magmas, overlap with the entire range of the regional flood basalt succession and do not form a coherent suite of Skaergaard like melts. These dykes are therefore re-interpreted as feeder dykes throughout the main phase of flood basalt volcanism.

To address the bulk compositions of CAIs from CH-CB chondrites we have used a new thermodynamic method to model the evaporation of CAI-like melts. The model calculations agree closely with the results of evaporation experiments on individual bulk compositions, and thus could provide a general means of predicting the evaporation trajectory of any CAI bulk composition melt. The model calculations and evaporation experiments show that the initial stages of CAI melt evaporation are controlled by the relative evaporation rates of MgO and SiO 2 , whereas the late stages are dominated by the initial CaO/Al 2 O 3 ratio of the melt. Application of the model to the puzzling bulk compositions of very refractory CAIs from CH-CB chondrites, many of which are grossite-, hibonite-, and spinel-rich, shows that such compositions can be derived via evaporation of precursors unusually enriched in Al 2 O 3 with CaO/Al 2 O 3 ratios (weight %) < 0.3. This rules out most silicate-rich CAI varieties. Only spinel- and spinel-hibonite-rich fine-grained inclusions with group II REE patterns (common in CV3 chondrites), which may have been present in the region where CH CAIs formed, could be precursors for the grossite- and hibonite-rich igneous CAIs. [ABSTRACT FROM AUTHOR]

The ability to apply automated quantitative mineralogy (AQM) on metamorphic rocks was investigated on samples from the Fiskenæsset complex, Greenland. AQM provides the possibility to visualize and quantify microstructures, minerals, as well as the morphology and chemistry of the investigated samples. Here, we applied the ZEISS Mineralogic software platform as an AQM tool, which has integrated matrix corrections and full quantification of energy dispersive spectrometry data, and therefore is able to give detailed chemical information on each pixel in the AQM mineral maps. This has been applied to create mineral maps, element concentration maps, element ratio maps, mineral association maps, as well as to morphochemically classify individual minerals for their grain shape, size, and orientation. The visualization of metamorphic textures, while at the same time quantifying their textures, is the great strength of AQM and is an ideal tool to lift microscopy from the qualitative to the quantitative level. [ABSTRACT FROM AUTHOR]

Eclogites, blueschists and greenschists are found in close proximity to one another along a 1‐km coastal section where the Cyclades Blueschist Unit (CBU) is exposed on SE Syros, Greece. Here, we show that the eclogites and blueschists experienced the same metamorphic history: prograde lawsonite blueschist facies metamorphism at 1.2–1.9 GPa and 410–530°C followed, at 43–38 Ma, by peak blueschist/eclogite facies metamorphism at 1.5–2.1 GPa and 520–580°C. We explain co‐existence of eclogites and blueschists by compositional variation probably reflecting original compositional layering. It is also shown that the greenschists record retrogression at 0.34 ± 0.21 GPa and T = 456 ± 68°C. This was spatially associated with a shear zone on a scales of 10–100‐m and veins on a scale of 1–10‐cm. Greenschist facies metamorphism ended at (or shortly after) 27 Ma. We thus infer a period of metamorphic quiescence after eclogite/blueschist facies metamorphism and before greenschist facies retrogression which lasted up to 11–16 million years. We suggest that this reflects an absence of metamorphic fluid flow at that time and conclude that greenschist facies retrogression only occurred when and where metamorphic fluids were present. From a tectonic perspective, our findings are consistent with studies showing that the CBU is (a) a high‐P nappe stack consisting of belts in which high‐P metamorphism and exhumation occurred at different times and (b) affected by greenschist facies metamorphism during the Oligocene, prior to the onset of regional tectonic extension. [ABSTRACT FROM AUTHOR]

Abstract The terrestrial planets are believed to have been formed from primitive material sampling a broad region of the inner solar system. Several meteoritic mixing models attempting to reconcile isotopic characteristics of Mars and Earth have been proposed, but, because of the inherent non-uniqueness of these solutions, additional independent observations are required to resolve the question of the primary building blocks of the terrestrial planets. Here, we consider existing isotopic measurements of Δ ′ 17 O, ϵ 48Ca, ϵ 50Ti, ϵ 54Cr, ϵ 62Ni, and ϵ 84Sr for primitive chondrites and differentiated achondrites and mix these stochastically to reproduce the isotopic signatures of Mars and Earth. For both planets we observe ∼ 105 unique mixing solutions out of 108 random meteoritic mixtures, which are categorised into distinct clusters of mixtures using principal component analysis. The large number of solutions implies that isotopic data alone are insufficient to resolve the building blocks of the terrestrial planets. To further discriminate between isotopically valid mixtures, each mixture is converted into a core and mantle component via mass balance for which geophysical properties are computed and compared to observations. For Mars, the geophysical parameters include mean density, mean moment of inertia, and tidal response, whereas for Earth upper mantle Mg/(Mg+Fe) ratio and core size are employed. The results show that Mars requires an oxidised, FeO-rich differentiated object next to chondritic material as main building blocks. In contrast, Earth's origin remains enigmatic. From a redox perspective, it appears inescapable that enstatite chondrite-like matter constitutes a dominant proportion of the building blocks from which Earth is made. The apparent need for compositionally distinct building blocks for Mars and Earth suggests that dissimilar planetesimal reservoirs were maintained in the inner Solar System during accretion. Highlights • Stochastic mixing of chondrites and achondrites to reconcile isotopic signatures for Mars and Earth indicates highly non-unique solution spaces. • Complementary geophysical and redox analysis is used further to discriminate between the various isotopically valid solutions. • Mars requires at least one oxidised object next to chondritic material as building block. • For Earth, a large proportion of unsampled enstatite chondrite-like material, seems to be essential. [ABSTRACT FROM AUTHOR]

The geochemical specificities of mountainous soils of Middle Ural on the example of Basegi Ridge were considered in this work. We calculated and analyzed geochemical coefficients of accumulation, subsurface weathering, eluviation and oxidation. It is shown that soil forming processes on Severniy Baseg Mountain don’t lead to the clear differentiation of the profile according to the content of one or another microelements. The level of concentrations of elements in landscapes was increased from elluvial to transaccumulative. This was determined by the increasing role of lateral distribution of concentration of chemical elements in mountainous ecosystems. This is confirmed by the calculated accumulation coeffecients and also by the results of cluster analysis. It shows that there are higher concentrations of Al, Fe, K, Ca, Mg, Mn in the soils of forest-mountainous belt, comparing to soils of goltsy altitudinal belt and subgoltsy altitudinal belt, and comparing to alpine belt. The analysis of the original data and literature sources confirmed that the climate change in the end of late Holocene affected dramatically on the climate change of mountainous part of western macroslope of Middle Ural.

Vibrational sum-frequency generation spectroscopy is a valuable probe of surface structure, particularly when the same molecules are present in one of the adjacent bulk solid or solution phases. As a result of the non-centrosymmetric requirement of SFG, the signal generated is a marker of the extent to which the molecules are ordered in an arrangement that breaks the up-down symmetry at the surface. In cases where the accompanying changes in the bulk are of interest in understanding and interpreting the surface structure, simultaneous analysis of the bulk IR absorption or bulk Raman scattering is helpful, and may be used in heterospectral surface-bulk two-dimensional correlation. We demonstrate that, in such cases, generating a new type of bulk spectrum that combines the IR and Raman amplitudes is a better candidate than the individual IR and Raman spectra for the purpose of correlation with the SFG signal. [ABSTRACT FROM AUTHOR]

Bulk chemical compositions of meteorites were traditionally analyzed by wet chemical analysis, and NIPR has data for 1162 meteorites as of September 2017. We discuss the classification of meteorites on the basis of these data. Chondrite data are distributed in an anomalously wide range of compositions on the Urey-Craig diagram. One of the reasons for such wide distribution is terrestrial weathering producing Fe 2 O 3 –bearing phases from Fe-Ni metal and sulfides. Another important factor affecting the bulk compositional data is brecciation. Our observations indicate that many brecciated chondrites contain anomalously abundant opaque minerals, or are depleted in them, resulting in unusual compositions. In case of enstatite and some carbonaceous chondrites, the bulk compositions are distributed in wider ranges than reported before. The bulk compositions of HED meteorites are consistent with their mineralogy and classification. Our study suggests that wet chemical data are still significant for the meteorite classification. However, petrographic observation is indispensable for evaluating the bulk chemistry and classification of meteorites. [ABSTRACT FROM AUTHOR]

A new macro-Raman system equipped with a motorized translational sample stage and low-frequency shift capabilities was developed for bulk composition and homogeneity analysis of multi-component pharmaceutical powders. Different sampling methods including single spot and scanning measurement were compared. It was found that increasing sample volumes significantly improved the precision of quantitative composition analysis, especially for poorly mixed powders. The multi-pass cavity of the macro-Raman system increased effective sample volumes by 20 times from the sample volume defined by the collection optics, i.e., from 0.02 μL to about 0.4 μL. A stochastic model simulating the random sampling process of polydisperse microparticles was used to predict the sampling errors for a specific sample volume. Comparison of fluticasone propionate mass fractions of the commercial products Flixotide ® 250 and Seretide ® 500 simulated for different sampling volumes with experimentally measured compositions verified that the effective sample volume of a single point macro-Raman measurement in the multi-pass cavity of this instrument was between 0.3 μL and 0.5 μL. The macro-Raman system was also successfully used for blend uniformity analysis. It was concluded that demixing occurred in the binary mixture of l -leucine and d -mannitol from the observation that the sampling errors indicated by the standard deviations of measured leucine mass fractions increased during mixing, and the standard deviation values were all larger than the theoretical lower limit determined by the simulation. Since sample volume was shown to have a significant impact on measured homogeneity characteristics, it was concluded that powder homogeneity analysis results, i.e., the mean of individual test results and absolute and relative standard deviations, must be presented together with the effective sample volumes of the applied testing techniques for any measurement of powder homogeneity to be fully meaningful. [ABSTRACT FROM AUTHOR]

Zero-valent iron nanoparticles (nZVI) have been widely tested as they are showing significant promise for environmental remediation. However, many recent studies have demonstrated that their mobility and reactivity in subsurface environments are significantly affected by their tendency to aggregate. Both the mobility and reactivity of nZVI mainly depends on properties such as particle size, surface chemistry and bulk composition. In order to ensure efficient remediation, it is crucial to accurately assess and understand the implications of these properties before deploying these materials into contaminated environments. Many analytical techniques are now available to determine these parameters and this paper provides a critical review of their usefulness and limitations for nZVI characterisation. These analytical techniques include microscopy and light scattering techniques for the determination of particle size, size distribution and aggregation state, and X-ray techniques for the characterisation of surface chemistry and bulk composition. Example characterisation data derived from commercial nZVI materials is used to further illustrate method strengths and limitations. Finally, some important challenges with respect to the characterisation of nZVI in groundwater samples are discussed. [ABSTRACT FROM AUTHOR]

The influence of the rock-forming additives kaolin and alumina in the presence of nickel compounds on the thermal catalytic conversion of heavy oil at a temperature of 360°C in a reducing atmosphere at different pressures in the system has been revealed. The effect of poly-α-olefins as a hydrogen donor has been examined. It has been found that there are predominant degradation reactions of the resinous components, aliphatic substituents in asphaltenes, and branched aliphatic structures accompanied by redistribution of n-alkanes toward homologues with a lower molecular weight, resulting in reduction in the viscosity of heavy oil. Conducting the process in the presence of AlO, Ni, and poly-α-olefins at a pressure of 8 MPa increases the quantity of light fractions of the oil and facilitates the degradation of asphaltenes. A decrease of pressure in the experiment on the oil with kaolin in a reducing atmosphere leads to a decrease in aromaticity of the final product and an increase in the yield of lube oil hydrocarbon and low-boiling fractions. [ABSTRACT FROM AUTHOR]

This paper investigates the drying behaviour and particle formation of emulsions modelled after a range of compositions observed in human milk at different lactation periods. The knowledge on drying kinetics would be relevant to understand important drying conditions in processing dairy products with similar compositional makeup while shrinkage kinetics and surface characterization provide a greater comprehension of the influence surface-active milk components have on product functionality. Droplet drying histories of model emulsions are presented through the glass-filament single droplet drying (SDD) method combined with the Reaction Engineering Approach (REA) modelling. For droplets with both initial solids of 20 wt.% and 40 wt.%, model emulsion (ME) with the highest lactose content exhibited the most shrinkage (normalized particle size being 0.68 and 0.81 respectively), followed by those with highest protein content (0.70 and 0.81), whereas those with the highest fat content showed the least shrinkage (0.73 and 0.84). In situ rehydration study found that ME with the highest fat content exhibited the earliest skin formation but delayed crust formation. The X-ray photoelectron spectroscopy (XPS) analysis which observed an overrepresentation of surface fat across all three MEs regardless of the drying technique indicated the occurrence of surface fat enrichment during ME droplet generation and drying processes. [ABSTRACT FROM AUTHOR]

In general the analysis of archeological glass represents a challenge for a wide variety of objects because of the presence of physical and/or chemical damage on the surface of the artifact, also known as weathering or corrosion. To retrieve accurate bulk elemental information by laser ablation-inductively coupled plasma-mass spectrometry (ICP-MS), the original, pristine glass needs to be 'reached', thereby penetrating the alteration layer which is often more than 10 μm thick. To study this alteration layer the laser was operated in the drilling mode, either with a low (1 Hz) or a high (10 Hz) pulse repetition rate for a period of 50 s yielding detailed spatial information for ca. 20 elements over a shallow depth (ca. 5 μm) or less-detailed spatial information for 50-60 elements over a greater depth (ca. 50 μm). Quantitative elemental depth profiles (in wt%) were obtained with the so-called sum normalization calibration protocol, based on summation of the elements as their oxides to 100 wt%. We were able to associate the increase of SiO (in wt%) in the alteration layer to the volumetric mass density change in the glass as a result of depletion of NaO and KO. Also the interaction of the number of laser shots with the alteration layer is shown experimentally via depth measurements using profilometry. Chemical and physical changes in four ancient glass artifacts, directly and indirectly measureable by laser drilling, were studied as a function of internal and external factors such as age, composition, and exposure conditions. [ABSTRACT FROM AUTHOR]

We evaluate the performance of a hand-held XRF ( HHXRF) spectrometer for the bulk analysis of iron meteorites. Analytical precision and accuracy were tested on metal alloy certified reference materials and iron meteorites of known chemical composition. With minimal sample preparation (i.e., flat or roughly polished surfaces) HHXRF allowed the precise and accurate determination of most elements heavier than Mg, with concentrations > 0.01% m/m in metal alloy CRMs, and of major elements Fe and Ni and minor elements Co, P and S (generally ranging from 0.1 to 1% m/m) in iron meteorites. In addition, multiple HHXRF spot analyses could be used to determine the bulk chemical composition of iron meteorites, which are often characterised by sulfide and phosphide accessory minerals. In particular, it was possible to estimate the P and S bulk contents, which are of critical importance for the petrogenesis and evolution of Fe- Ni-rich liquids and iron meteorites. This study thus validates HHXRF as a valuable tool for use in meteoritics, allowing the rapid, non-destructive (a) identification of the extraterrestrial origin of metallic objects (i.e., archaeological artefacts); (b) preliminary chemical classification of iron meteorites; (c) identification of mislabelled/unlabelled specimens in museums and private collections and (d) bulk analysis of iron meteorites. [ABSTRACT FROM AUTHOR]

We have studied a computer simulations of the surface structure and chemical composition in NiAl for three low index surface orientations and three bulk compositions. We have applied a grand canonical Monte Carlo method in conjuction with a embedded atom potential fit to a large database. We found that the chemical composition of the (110) surface is very close to the bulk composition. For the (100) and (111) surface orientations, the Al termination contains some percentage of Ni atoms in the form of antisites and for the (111) orientation also a significant amount of surface vacancies and adatoms exist. The Ni termination of both surfaces are unstable and transform to Al terminations. [ABSTRACT FROM AUTHOR]

Abstract: The LIBSSIM program was developed to aid in understanding data returned by the laser-induced breakdown spectrometer (LIBS) on Mars Science Laboratory (MSL). The program models the effects of rock grain size, mineralogy, sampling density, and beam size on inferred bulk chemical analyses using Martian basaltic compositions. The relationship between grain size and beam size was found to be the most important factor in producing a representative LIBSSIM-predicted bulk composition. As grain size increases relative to beam size, accuracy of calculated bulk compositions decreases, but chemical information about the nature of the component grains is improved. Sampling density takes on greatest importance in coarse-grained samples with large compositional differences among grains, where many analyses are required to reduce standard deviations to acceptable levels. These results stress the importance of careful sampling strategies for the LIBS at the MSL landing site at Gale crater. [Copyright &y& Elsevier]

Abstract: We analyzed chemical composition and electron transport phenomena in surface and sub-surface region of hot-pressed TiN specimens using a combination of X-ray photoelectron spectroscopy (XPS) and elastic-peak electron spectroscopy (EPES) techniques. Both the surface chemical composition and the elements distribution in the bulk of TiN specimens were determined using XPS and XPS depth profiling analysis. In addition to TiN, a mixture of Ti oxynitride (TiO x N y ) and TiO2 compounds as well as carbon contaminants have been detected in the surface region of the TiN specimens. The elemental depth-profiles disclosed uniform chemical bulk composition formed mainly by titanium and nitrogen as well as carbon and oxygen contaminants. Surface enrichment of Ti was evidenced as result of Ar ion-induced preferential sputtering of nitrogen. The inelastic mean free path (IMFP) data evaluated from the relative EPES for electron energies 0.5–2keV were uncorrected for surface excitations and compared with those calculated from the predictive TPP-2M formula for the measured surface composition. Except to the electron energy of 0.5keV, a good agreement was found between the measured and predicted IMFPs in the TiN specimen. The higher discrepancies in the measured IMFPs at the lowest energy can be explained by the surface excitation effect. The smallest root-mean-square-deviation and the mean percentage deviation of 2.8Å and 14.8%, respectively, were found between EPES IMFP data and those predicted for TiN with respect to the Ni standard. [Copyright &y& Elsevier]

Abstract: This paper presents a review of bulk compositional data of northern African dust and its potential source sediments and includes elemental, isotope and mineralogical data. Northern African dust represents about one half of the total global atmospheric mineral dust burden, and its uplift, transport and deposition have strong impacts on climate and various terrestrial and marine ecosystems. The chemical data set shows, that an ‘average northern African dust’ exhibits comparable Si, Fe and Mn contents with respect to the average composition of the upper continental crust, is slightly depleted in the alkali metals K and Na, and enriched in Ti and P. However, the complete data set yields clear evidence that northern African dust and its source sediments are compositionally heterogeneous on a regional scale and that this heterogeneity can be used to differentiate between major potential source areas on the basis of so-called source markers. An evaluation of these compositional fingerprints shows that the following parameters and especially their combination are effective in the discrimination of the most active source areas in northern Africa: ratio of (Ca+Mg)/Fe [wt.%], calcite (or carbonate) content, palygorskite occurrence and abundance, illite/kaolinite ratio, ƐNd(0) value, and 87Sr/86Sr ratio. For example, the data set corroborates previous ideas, which assign carbonate-, illite- and palygorskite-rich mineral dusts to north(west)ern source regions. Because most of the above listed source markers do not change substantially during transport, even far-traveled dusts may be assigned to specific potential source areas in northern Africa. Some limitations of the presented data set are also discussed. Our compilation reveals some substantial gaps in the knowledge of the composition of source sediments and mineral dusts from important potential source areas that should be filled in the future. The here compiled data set can be used as a reference frame, when incorporating the composition of source sediments (e.g., mineralogy) into global or regional dust transport models and can be compared with source analysis by remote sensing or back-trajectory analysis. However, source apportionment studies supported by our data set will not only be useful for actual dust samples, but will also be helpful for the understanding of paleo-wind directions and hence paleo-climatological conditions through the investigation of Quaternary eolian sediments deposited in and around northern Africa. [Copyright &y& Elsevier]

We have studied a computer simulations of the surface structure and chemical composition in NiAl for three low index surface orientations and three bulk compositions. We have applied a grand canonical Monte Carlo method in conjuction with a embedded atom potential fit to a large database. We found that the chemical composition of the (110) surface is very close to the bulk composition. For the (100) and (111) surface orientations, the Al termination contains some percentage of Ni atoms in the form of antisites and for the (111) orientation also a significant amount of surface vacancies and adatoms exist. The Ni termination of both surfaces are unstable and transform to Al terminations. [ABSTRACT FROM AUTHOR]

Abstract: Since 1994, the Rumuruti (R) chondrites have been recognized as a new, well-established chondrite group differing from carbonaceous, ordinary, and enstatite chondrites. The first R chondrite, Carlisle Lakes, was found in Australia in 1977. Meanwhile, the number has increased to 107 (December, 2010). This group is named after the Rumuruti meteorite, the first and so far the only R chondrite fall. Most of the R chondrites are breccias containing a variety of different clasts embedded in a clastic matrix. Some textural and mineralogical characteristics can be summarized as follows: (a) the chondrule abundance in large fragments and in unbrecciated rocks is ∼35–50vol%; (b) Ca,Al-rich inclusions are rare; (c) the olivine abundance is typically 65–78vol%; (d) the mean chondrule diameter is ∼400μm; (e) in unequilibrated R chondrites, low-Ca pyroxene is dominating, whereas in equilibrated R chondrites it is Ca-rich pyroxene; (f) the typical olivine in a metamorphosed lithology is ∼Fa38–40; (g) matrix olivine in unequilibrated, type 3 fragments and rocks has much higher Fa (∼45–60mol%) compared to matrix olivines in type 4–6 lithologies (∼Fa38–41); (h) spinels have a high TiO2 of ∼5wt%; (i) abundant different noble metal-bearing phases (metals, sulfides, tellurides, arsenides) occur. The exception is the metamorphosed, type 5/6 R chondrite La Paz Icefield 04840 which contains hornblende, phlogopite, and Ca-poor pyroxene, the latter phase typically occurring in low-grade metamorphosed R chondrites only. In bulk composition, R chondrites have some affinity to ordinary chondrites: (a) the absence of significant depletions in Mn and Na in R chondrites and ordinary chondrites is an important feature to distinguish these groups from carbonaceous chondrites; (b) total Fe (∼24wt%) of R chondrites is between those of H and L chondrites (27.1 and 21.6wt%, respectively); (c) the average CI/Mg-normalized lithophile element abundances are ∼0.95×CI, which is lower than those for carbonaceous chondrites (≥1.0×CI) and slightly higher than those for ordinary chondrites (∼0.9×CI); (d) trace element concentrations such as Zn (∼150ppm) and Se (∼15ppm) are much higher than in ordinary chondrites; (e) the whole rock Δ17O of ∼2.7 for R chondrites is the highest among all meteorite groups, and the mean oxygen isotope composition is δ17O=5.36±0.43, δ18O=5.07±0.86, Δ17O=+2.72±0.31; (f) noble gas cosmic ray exposure ages of R chondrites range between ∼0.1 and ∼70Ma. More than half of the R chondrites analyzed for noble gases contain implanted solar wind and, thus, are regolith breccias. The 43 R chondrites from Northern Africa analyzed so far for noble gases seem to represent at least 16 falls. Although the data base is still scarce, the data hint at a major collision event on the R chondrite parent body between 15 and 25Ma ago. [Copyright &y& Elsevier]

• An error in the previously reported bulk composition of a PdAg(111) alloy is corrected. • Bulk-sensitive energy-dispersive X-ray spectroscopy (EDS) was used to correctly determine the bulk composition of the material. Investigation of isolated, single atoms on the surfaces of alloys is of great interest in the field of heterogeneous catalysis. Prior studies by Nieuwenhuys, etal. [ Surf. Sci. 417 (1998) 292–300 and references therein] showed that annealing the (111) surface of a PdAg bulk alloy yielded a surface with ∼5% Pd, predominantly in the form of single atoms, rendering it an ideal model for investigating the reactivity of single Pd atoms. Herein, new evidence is reported that establishes the bulk composition of the PdAg(111) alloy studied previously is 67% Ag and 33% Pd, whereas it was reported to be 33% Ag and 67% Pd in the prior studies. Herein, the bulk composition of a crystal derived from the same PdAg alloy boule used previously was determined using energy-dispersive X-ray spectroscopy (EDS)—a bulk sensitive technique. Surface-sensitive measurements, including X-ray photoelectron spectroscopy, were also performed and are in good agreement with the prior studies by Nieuwenhuys, etal. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The foremost principles of experimental igneous petrology applied to natural rocks are here considered to be the following. First, only the mineral assemblages found at or near the experimental liquidus are relevant to fractional crystallization. Subliquidus assemblages of the same bulk composition can have little relevance to this process, owing to the closed system of the experiment. Second, in a closed system the natural mineral assemblages define the intensive parameters of T, P, and the activities of all components, including oxygen, which must constrain the experimental investigation. Extensive (mass-dependent) parameters do not define the compositions of the evolving liquids, which are solely controlled by successive liquidus phase assemblages. Third, the bulk compositions (rocks or mixtures) chosen for study must be able to yield at the liquidus the mineral compositions found in the natural occurrence. The study under discussion fails in all three of these desiderata. Subliquidus products of equilibrium crystallization and their masses were used to infer a differentiation history. Intensive parameters were constrained to an arbitrary choice of the FMQ buffer. Finally, the bulk compositions chosen for experiment can be shown beforehand (and as in the listed results) to yield olivine and plagioclase compositions far more refractory than in any known rock of the target intrusion. [Copyright &y& Elsevier]

Multiphased mixed crystals were grown by the melt method, for the first time, using the miscible alkali halides, namely, NaBr and KCl. X-ray powder diffraction measurements indicate the existence of multiple phases and mostly of ternary mixed alkali halides. Density and refractive index were measured and the composition was determined. Results are reported. [ABSTRACT FROM AUTHOR]

(MoVW)5O14-type oxides were identified as the active and selective components in industrial acrylic acid catalysts. Tungsten is suggested to play an important role as a structural promoter in the formation and stabilization of this oxide. Vanadium is responsible for high catalytic activities but is detrimental for the stability of this oxide at the necessary high concentrations for optimum catalytic performance. The activity of mixed MoVW oxide catalysts for methanol, propene, and acrolein partial oxidation could be considerably improved, when the amount of the (MoVW)5O14-type oxide was increased by thermal annealing. A model is proposed on the basis of the correlation between Raman wavenumber and bond order and degree of reduction, which explains the observed different selectivities of MoO3− x and the (MoVW)5O14-type oxides in terms of metal–oxygen bond strengths, i.e. oxygen basicity and oxygen lability, respectively. According to this model, the (MoVW)5O14 mixed oxide catalyses partial oxidation because of its intermediate C–H activation and oxygen releasing oxygen functionalities. However, these (MoVW)5O14-type industrial oxidation catalysts are heterogeneous and highly complex systems. Their physicochemical characterization also revealed that their chemical bulk and surface compositions vary with thermal activation and oxygen potential. A core-shell model is suggested to describe the active catalyst state, the shell providing a high number of active centers, the core high electronic conductivity and ion mobility. The fact that the surface composition of such catalysts is considerably different from their bulk compositions, most probably implies that the “molecular structure” at their surface differs too considerably from their bulk crystal structure. Hence, the posed question about the active catalyst structure and its relation to its catalytic performance cannot unambiguously be explained by the crystallographic structure, but still remains unsolved. [ABSTRACT FROM AUTHOR]