Analysis Of Individual Grains Research Articles

Higher water content observed in smaller size fraction of Chang'e-5 lunar regolith samples

Water has been detected in lunar regolith, with multiple sources identified through the analysis of individual grains. However, the primary origin of water in the bulk lunar regolith remains uncertain. This study presents spectroscopic analyses of water content in sealed Chang'e-5 samples. These samples were sieved into various size fractions (bulk, <45 μm, and 45–355 μm) inside a glovebox filled with high-purity nitrogen. Results indicate a higher water content in the fine fractions (∼87 ± 11.9 ppm) than in bulk soil (∼37 ± 4.8 ppm) and coarse fractions (∼11 ± 1.5 ppm). This suggests that water is predominantly concentrated in the outermost rims of the regolith grains, and thus exhibits dependence on the surface volume ratio (also known as surface correlation), indicating solar wind is a primary source of lunar surface water. Laboratory, in-situ, and orbital results bridge sample analysis and remote sensing, offering a cohesive understanding of lunar surface water characteristics as represented by Chang'e-5. The discovery provides statistical evidence for the origin of water in lunar soil and can be considered representative of the lunar surface conditions. The water enrichment of the finest fraction suggests the feasibility of employing size sorting of lunar soils as a potential technological approach for water resource extraction in future lunar research stations.

A combined LM and SEM study of selected palynomorphs from the palaeoflora of the Paleocene Konservat-Lagerstätte Menat (Puy-de-Dôme, France)

ABSTRACT In the course of a pilot study on the palynology of the late Paleocene (Thanetian) maar deposits of Menat (Puy-de-Dôme, Auvergne, France), selected palynomorphs were analysed with the single grain technique. This technique allows for a consecutive analysis of individual grains by means of light microscopy and Scanning Electron Microscopy (SEM). The current study demonstrates the occurrence of diverse lineages of palynomorphs comprising algae, spores and pollen. So far 45 different types of palynomorphs were analysed, illustrated and wherever possible assigned to families encompassing chlorococcalean and zygnematalean algae, ferns, gymnosperms and angiosperms. The latter group was the most diverse one among the analysed palynomorphs. The palynomorphs described in this study represent only a small, non-representative selection of palynomorphs that occur in the palynoflora of the maar lake from Menat, and hence more effort is expected to be done in the future. However, the data and interpretations presented here are preliminary ones, they could help to understand and refine our knowledge about the palaeoflora and palaeoenvironments of this important locality and fossil archive, as well as their development through time.

In situ Rb-Sr dating of slickenfibres in deep crystalline basement faults

Establishing temporal constraints of faulting is of importance for tectonic and seismicity reconstructions and predictions. Conventional fault dating techniques commonly use bulk samples of syn-kinematic illite and other K-bearing minerals in fault gouges, which results in mixed ages of repeatedly reactivated faults as well as grain-size dependent age variations. Here we present a new approach to resolve fault reactivation histories by applying high-spatial resolution Rb-Sr dating to fine-grained mineral slickenfibres in faults occurring in Paleoproterozoic crystalline rocks. Slickenfibre illite and/or K-feldspar together with co-genetic calcite and/or albite were targeted with 50 µm laser ablation triple quadrupole inductively coupled plasma mass spectrometry analyses (LA-ICP-MS/MS). The ages obtained disclose slickenfibre growth at several occasions spanning over 1 billion years, from at least 1527 Ma to 349 ± 9 Ma. The timing of these growth phases and the associated structural orientation information of the kinematic indicators on the fracture surfaces are linked to far-field tectonic events, including the Caledonian orogeny. Our approach links faulting to individual regional deformation events by minimizing age mixing through micro-scale analysis of individual grains and narrow crystal zones in common fault mineral assemblages.

Age discordance and mineralogy

Observations of discordant ages, meaning that an age given by one mineral geochronometer is different from the age given by another geochronometer from the same rock, began in the early days of geochronology. In the late 1950s and 1960s, discordant U-Pb zircon ages were unquestioningly attributed to Pb diffusion at high temperature. Later, the mineralogical properties and the petrogenesis of the zircon crystals being dated was recognized as a key factor in obtaining concordant U-Pb ages. Advances in analytical methods allowed the analysis of smaller and smaller zircon multigrain fractions, then the analysis of individual grains, and even pieces of grains, with higher degrees of concordancy. Further advances allowed a higher analytical precision, a clearer perception of accuracy, and a better statistical resolution of age discordance. As for understanding the cause(s) of discordance, belief revision followed the coupling of imaging, cathodoluminescence (CL) and back-scattered electrons (BSE), to in situ dating by secondary ion mass spectrometry (SIMS), or by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Discordant zircon and other accessory minerals (e.g., monazite, apatite, etc.) often consist of young rims accreted onto/into older cores. Age gradients are sharp, and no Pb diffusion gradients are observed. As U-Pb discordance in crystalline, non-radiation damaged grains is caused by diachronous, heterochemical mineral generations, interpretations of mineral ages, based on the exclusive role of diffusion, are superseded, and closure temperatures of zircon and monazite are irrelevant in geological reality. Other isotopic systems (Rb-Sr, K-Ar) were believed, since the 1960s, to be similarly controlled by the diffusivity of radiogenic daughters. When zircon and monazite discordance were recognized as zone accretion/reaction with sharp boundaries that showed little or no high-temperature diffusive re-equilibration, the other chronometric systems were left behind, and interpretations of mineral ages based on the exclusive role of diffusion survived. The evidence from textural-petrologic imaging (CL, BSE) and element mapping by electron probe microanalyzer (EPMA) or high spatial resolution SIMS or LA-ICPMS provides the decisive constraints. All microcline and mica geochronometers that have been characterized in detail document patchy textures and evidence for mineral replacement reactions. It is important not to confuse causes and effects; heterochemical microstructures are not the cause of Ar and Sr loss; rather, they follow it. Argon and Sr loss by dissolution of the older mineral generation occurs first, heterochemical textures form later, when the replacive assemblage recrystallizes. Heterochemical mineral generations are identified and dated by their Ca/Cl/K systematics in 39Ar-40Ar. Replacive reactions adding or removing Cl, such as, e.g., sericite overgrowths on K-feldspar, retrograde muscovite intergrowths with phengite, etc., are detected by Cl/K vs Ar/K isotope correlation diagrams. Calcium-poor reaction products, such as, e.g., young biotite intergrown with older amphibole, adularia replacing microcline, etc., can be easily identified by Ca/K vs Ar/K diagrams supported by EPMA analyses. Mixed mineral generations are observed to be the cause of discordant, staircase-shaped age spectra, while step-heating of crystals with age gradients produces concordant plateaus. Age gradients are therefore unrelated to staircase age spectra. There is a profound analogy between the U-Pb, Rb-Sr, and K-Ar systems. Lead and Ar diffusion rates are both much slower than mineral replacement rates for all T < 750 °C. Patchy retrogression textures are always associated with heterochemical signatures (U/Th ratios, REE patterns, Ca/Cl/K ratios). As a rule, single-generation minerals with low amounts of radiation damage give concordant ages, whereas discordance is caused by mixtures of heterochemical, resolvably diachronous, mineral generations in petrologic disequilibrium. This can also include (sub-)grains that have accumulated significant amounts of radiation damage. For accurate geochronology the petrologic characterization with the appropriate technique(s) of the minerals to be dated, and the petrologic context at large, are as essential as the mass spectrometric analyses.

Why Is Li2MnSiO4 Unstable in Li-Ion Battery Cell? Structural Studies at Different Stages of Electrochemical Reaction

Application of orthosilicates Li2MSiO4 (M=Fe, Mn, Co, Ni) compounds as insertion materials for LIBs was firstly proposed by Prof. Goodenough [1]. The materials mainly crystallize in orthorhombic system of Pmn21 space group in olivine structure [2-4]. The Li2MSiO4 olivine structure may be described as wavy layers of [SiMO4]∞ on ac axis plane and connected along b axis by LiO4 tetrahedra [2]. Within the layers every SiO4 tetrahedron shares its corner with four next MO4 tetrahedra. Lithium ions occupy the tetrahedral sites (LiO4) between two layers and share 3 and 1 oxygen atoms with the layers. In fact, diffusion of lithium ions in this structure is possible only through the canals formed by LiO4 tetrahedra. Li2MSiO4 silicates reveal a possibility of reversible insertion of two lithium ions per molecule, which leads to exchange of two electrons by transition metal. As a results the silicates reveal high theoretical capacity, up to 330 mA/g for Li2MnSiO4 (LMS). LMS, which works at potentials 4.2 and ~4.5 V for first and second redox reactions respectively, seems to be the most useful from all of dilithiumorthosilicates family compounds. The main disadvantage of LMS is its extremely low electrical conductivity [2,5] and structural instability [7-11]. While the conductivity issues can be fixed by the preparation of nanograined material and its modification by carbon coating, similarly to the procedures applied in case of LiFePO4, the reasons of structural instability of LMS are not entirely known. There is a number of reports showing that Li2MnSiO4 cathode material undergoes amorphization in the first few charging/discharging cycles but there is no comprehensive explanation of this phenomenon. The degradation of crystalline structure can be caused by Jahn–Taller distortion associated with changes in lattice parameters during Mn3+→Mn4+ transition [8]. Another explanation may be the occurrence of secondary reactions between electrolyte and delithated forms of lithium manganese silicate (LiMnSiO4 and MnSiO4). The aforementioned structural changes of the material entail variations in electrochemical properties of Li2MnSiO4[9]. The goal of this studies is to examine structural instability of Li2MnSiO4which occurs in first electrochemical charging/discharging cycle via microscopic analysis of individual grains at different stages of electrochemical reaction. The Li2MnSiO4material was prepared using Pechini's sol–gel method which was previously reported by our group [9-11]. The structural changes in the material was studied using in-situ X-Ray diffraction as well as ex-situ transmission electron microscopy. To determine degradation mechanism of Li2MnSiO4 and C/Li2MnSiO4 in working Li-ion cell two different aspects of LMS performance were analyzed. Firstly corrosive properties of liquid electrolytes were taken under consideration. Solubility of manganese from LMS and C/LMS samples (occurring during electrochemical reaction) in LiPF6solution in EC:DMC (1:1) was studied. On the other hand using in-situ XRD and ex-situ TEM analysis in different SOC (in initial cycle in 1.5-4.8V potential range) the process of amorphization of crystalline LMS was examined. ACKNOWLEDGMENT This work is supported by National Science Centre, Poland under research grant no. 2014/13/B/ST5/04531. REFERENCES Padhi A.K., Nanjundaswamy K.S., Goodenough J.B. J. Electrochem. Society 144 (1997) 1188-1194.M.E. Arroyo-de Dompablo, M. Armand, J.M. Tarascon, U. Amator, Electrochem. Commun. 8 (2006) 1292–1298.A. Nyten, A. Abouimrane, M. Armand, T. Gustafsson, J.O. Thomas, Electrochem. Commun. 7 (2005) 156–160.Z.L. Gong, Y.X. Li, Y. Yang, J. Power Sources 174 (2007) 524–527.A. Kokalj, R. Dominko, G. Mali, A. Meden, M. Gaberscek, J. Jamnik, Chem. Mater. 19 (2007) 3633–3640.R. Dominko, M. Bele, M. Gaberscek, A. Meden, M. Remskar, J. Jamnik, Electrochem. Commun. 8 (2006) 217–222.R. Dominko, M. Bele, A. Kokalj, M. Gaberscek, J. Jamnik, J. Power Sources 174 (2007) 457–461.Y.-X. Li, Z.-L. Gong, Y. Yang, J. Power Sources 174 (2007) 528–532.M. Świętosławski, M. Molenda, M. Grabowska, A.Wach, P. Kuśtrowski, R. Dziembaj, Solid State Ionics 263 (2014) 99–102M. Molenda, M. Świętosławski, A. Rafalska-Łasocha, R. Dziembaj, Funct. Mater. Lett. 4 (2011) 135–138.M. Świętosławski, M.Molenda, K. Furczoń, R. Dziembaj, J. Power Sources 244 (2013) 510–514.

BiFeO3 thin films via aqueous solution deposition: a study of phase formation and stabilization

This paper reports a thorough microstructural investigation of bismuth ferrite (BFO) thin films subjected to various processing conditions and discusses their influence on the stability of the BiFeO3 perovskite phase. The formation of secondary phases in BFO thin films is studied as a function of annealing temperature and time, film thickness, Bi excess, and Ti substitution. While films annealed at 600 °C consist of the desired BiFeO3 phase, higher temperatures induce the decomposition leading to a significant amount of secondary phases, particularly the iron-rich Bi2Fe4O9 phase. A longer annealing time at 700 °C further enhances the decomposition of BiFeO3. Qualitative microstructural analysis of the films is performed by electron backscattered diffraction which provides phase analysis of individual grains. The morphology of the single-crystalline Bi2Fe4O9 grains that are embedded in the BiFeO3 matrix drastically changes as a function of the film thickness. Nucleation of these Bi2Fe4O9 grains probably occurs at the film/substrate interface, after which grain growth continues toward the surface of the film through the depletion of the BFO phase. Addition of Bi excess or the substitution of Fe with Ti in the precursor solutions significantly reduces the formation of an iron-rich secondary phase. Influence of the secondary phases as well as Ti substitution on magnetic properties of BFO films was investigated.

Volcanic ash particulate matter from the 2010 Eyjafjallajökull eruption in dust deposition at Prague, central Europe

Abstract Particles originating from the last major Eyjafjallajokull volcano eruption in April 2010 were subsequently found in settled dust samples collected in a suburban area of Prague, Czech Republic. These dust samples contained predominantly non-volcanic particulate matter of super-regional but mainly local origin. The highest proportion of the Eyjafjallajokull material recorded in the Prague daily dust samples reached 12% of the total lithic component mass. Volcanogenic particles, mostly glasses, were concentrated in particle size classes from 2.5 to 25 μm, but rare fragments of volcanic glasses up to 50 μm in diameter were also found. The most effective method for detection and identification of the volcanic ash particles were morpho-textural observations combined with energy dispersive and wavelength dispersive analysis of individual grains and X-ray powder diffraction. Because of the low percentage of volcanic ash particles in the total samples, the geochemical signal was rather weak although detectable in terms of selected trace elements and REE distributions. The mineralogy, particle size distributions, and geochemical compositions of the Prague samples were compared with reference materials sampled near the Eyjafjallajokull volcano.

A case for landing on the moon's farside to test nitrogen abundances

AbstractA high research priority in astrobiology is the search and eventual identification of biomarkers in the Solar System. In spite of numerous steps forward, lunar science remains largely disjoint from the main stream of astrobiology, but in recent years the Moon has begun to emerge as a novel target for astrobiologists. We discuss an overlap between lunar geology and terrestrial geomicrobiology that arises from analysis of lunar soils and some uncertainties in chemical evolution and the origin of life scenarios. Unexpected isotopic heterogeneity of nitrogen (N) was found to be remarkable in samples from Apollo and the Luna programme. Both the stable isotope geochemical data of the biogenic elements, as well as the noble gases trapped in lunar soils added valuable new and relevant data. These discoveries are potential sources of information on early Earth evolution. The elusive ratio of N's two stable isotopes 15N/14N has played a fundamental role in this research. The analysis of individual grains of ilmenite suggests that 90% of all the trapped N does not originate from solar wind (SW). We discuss the significance of these stable isotopes from the point of view of astrobiology in the light of the next generation of lunar exploration. We underline the high priority of testing the origin of non-solar N source trapped in the regolith of the lunar farside. In the proposals of new lunar missions, the characterization of the geochemistry at several lunar sites is a major objective. Some arguments are presented in favour of using novel space technologies in a search for biomarkers in geographical distinct lunar landing sites. We restrict our attention to one aspect of the science requirements for the forthcoming missions by focusing on a very limited objective: to take a closer look at the geochemical characterization of the chemical element N on the soils of the lunar farside.

Using SPIRAL (Single Pollen Isotope Ratio AnaLysis) to estimate C 3- and C 4-grass abundance in the paleorecord

C 3 and C 4 grasses differ greatly in their responses to environmental controls and influences on biogeochemical processes (e.g. water, carbon, and nutrient cycling). Difficulties in distinguishing between these two functional groups of grasses have hindered paleoecological studies of grass-dominated ecosystems. Stable carbon isotopic analysis of individual grains of grass pollen using a spooling-wire microcombustion device interfaced with an isotope-ratio mass spectrometer holds promise for improving C 3 and C 4 grass reconstructions. This technique, SPIRAL (Single Pollen Isotope Ratio AnaLysis), has only been evaluated using pollen of known C 3 and C 4 grasses. To test the ability of SPIRAL to reproduce the abundance of C 3 and C 4 grasses on the landscape, we measured δ 13C values of > 1500 individual grains of grass pollen isolated from the surface sediments of ten lakes in areas that span a large gradient of C 3- and C 4-grass abundance, as determined from vegetation surveys. Results indicate a strong positive correlation between the δ 13C-based estimates of % C 4-grass pollen and the abundance of C 4 grasses on the landscape. The % C 4-grass pollen slightly underestimates the actual abundance of C 4 grasses at sites with high proportions of C 4 grasses, which can be corrected using regression analysis. Comparison of the % C 4-grass pollen with C/N and δ 13C measurements of bulk organic matter illustrates the distinct advantages of grass-pollen δ 13C as a proxy for distinguishing C 3 and C 4 shifts within the grass family. Thus SPIRAL promises to advance our understanding of grassland ecology and evolution.

Optically stimulated luminescence dating of single and multiple grains of quartz from perennially frozen loess in western Yukon Territory, Canada: Comparison with radiocarbon chronologies for the late Pleistocene Dawson tephra

Optically stimulated luminescence (OSL) dating of perennially frozen loess was tested on quartz grains extracted from deposits associated with the late Pleistocene Dawson tephra in western Yukon Territory, Canada. OSL samples were obtained from ice-rich loess bracketing the Dawson tephra, while radiocarbon ( 14C) samples were collected from the bulk sediments directly underlying the tephra and from a ground-squirrel burrow 2.7 m below the tephra. Here we report the OSL characteristics and ages of the extracted quartz grains, as well as additional radiocarbon ages for samples described in Froese [2002. Age and significance of the late Pleistocene Dawson tephra in eastern Beringia. Quaternary Science Reviews 21, 2137–2142; 2006. Seasonality of the late Pleistocene Dawson tephra and exceptional preservation of a buried riparian surface in central Yukon Territory, Canada. Quaternary Science Reviews 25, 1542–1551]. We refine the time of Dawson tephra deposition to between 25,420±70 and 25,290±80 14C a BP. Bayesian analysis of constraining radiocarbon ages places the deposition of the Dawson tephra at between 30,433 and 30,032 cal a BP. Linear modulation (LM) OSL analysis of multi-grain aliquots of quartz showed that the initial part of the decay curve is dominated by a rapidly bleached (‘fast’) component; these samples, however, had relatively dim continuous wave (CW) OSL signals at the multi-grain aliquot (each composed of ∼80 grains) and single-grain scales of analysis. The single-aliquot regenerative-dose protocol was applied to multi-grain aliquots and single grains to obtain equivalent dose ( D e) values for samples collected from below and above the Dawson tephra. The D e values were examined graphically and numerically, the latter using the central age, minimum age, and finite mixture models. For multi-grain aliquots, the central age model gave weighted mean D e values between 30 and 50 Gy, which greatly underestimated the expected D e of ∼74–81 Gy for both samples studied. Possible reasons for these underestimations are discussed, and a solution proposed based on single-grain analysis. Measurements of single grains produced D e values in agreement with the expected D e, and yielded OSL ages of 28±5 and 30±4 ka for the samples taken from above and below the Dawson tephra, respectively. Examination of individual grains with differing luminescence behaviors showed that a significant number of the measured quartz grains exhibited anomalous luminescence properties that would have compromised the results obtained from multi-grain aliquots. We therefore recommend analysis of individual grains to overcome the age-shortfall from multi-grain analysis of these and similar samples of quartz.

Analysis of equivalent-dose distributions for single grains of quartz from modern deposits

Two modern coastal sands are studied through single-grain optical dating techniques. The first sample is estimated to be less than 10 y old by means of independent age control and is known to be well-bleached on the basis of preliminary single-aliquot studies. The second sample is less than 1 y old, but an age of 73±24 years had been determined through single-aliquot analysis. For both samples we compare equivalent doses obtained from single-grain analysis to those obtained by means of similar single-aliquot methods. We found that results are comparable although equivalent doses determined through single-aliquot methods are more precise. The reason for this may be ascribed to the limited number of grains on which single-grain measurements were carried out. The presence of poorly bleached grains within a sample could be identified by dose distribution analysis of individual grains.

Automated Analysis of Imbrication and Flow Direction in Alluvial Sediments Using Laser-Scan Data

Abstract An automated method for analysis of imbrication and flow direction in alluvial sediments is described that uses digital elevation models (DEMs) derived from three-dimensional laser scanning of dry gravel river beds. A global analysis of the DEM is used that does not depend on location and analysis of individual grains. The method is more convenient and quantitative than are existing techniques. Methods are described for determining the suitability of particular data sets for analysis by this method. The method is applied to gravel river beds on the South Island of New Zealand.

Impact of irrigating rice paddies with groundwater containing arsenic in Bangladesh

Soil and soil–water As profiles were obtained from 4 rice paddies in Bangladesh during the wet growing season (May–November), when surface water with little arsenic is used for irrigation, or during the dry season (January–May), when groundwater elevated in arsenic is used instead. In the upper 5 cm of paddy soil, accumulation of 13 ± 12 mg/kg acid-leachable As ( n = 11) was observed in soil from 3 sites irrigated with groundwater containing 80–180 μg/L As, whereas only 3 ± 2 mg/kg acid-leachable As ( n = 8) was measured at a control site. Dissolved As concentrations averaged 370 ± 340 μg/L ( n = 7) in the upper 5 cm of the soil at the 3 sites irrigated with groundwater containing 80–180 μg/L As, contrasting with soil water As concentrations of only 18 ± 7 μg/L ( n = 4) over the same depth interval at the control site. Despite the accumulation of As in soil and in soil water attributable to irrigation with groundwater containing elevated As levels, there is no evidence of a proportional transfer to rice grains collected from the same sites. Digestion and analysis of individual grains of boro winter rice from the 2 sites irrigated with groundwater containing 150 and 180 μg/L As yielded concentrations of 0.28 ± 0.13 mg/kg ( n = 12) and 0.44 ± 0.25 mg/kg ( n = 12), respectively. The As content of winter rice from the control site was not significantly different though less variable (0.30 ± 0.07; n = 12). The observations suggest that exposure of the Bangladesh population to As contained in rice is less of an immediate concern than the continued use of groundwater containing elevated As levels for drinking or cooking, or other potential consequences of As accumulation in soil and soil–water.

Geochronology of weathering and landscape evolution, Dugald River valley, NW Queensland, Australia

40Ar/ 39Ar laser incremental heating analyses of individual grains of supergene jarosite, alunite, and cryptomelane from weathering profiles in the Dugald River area, Queensland, Australia, show a strong positive correlation between a sample’s age and its elevation. We analyzed 125 grains extracted from 35 hand specimens collected from weathering profiles at 11 sites located at 3 distinct elevations. The highest elevation profile hosts the oldest supergene minerals, whereas progressively younger samples occur at lower positions in the landscape. The highest elevation sampling sites (three sites), located on top of an elongated mesa (255 to 275 m elevation), yield ages in the 16 to 12 Ma range. Samples from an intermediate elevation site (225 to 230 m elevation) yield ages in the 6 to 4 Ma range. Samples collected at the lowest elevation sites (200 to 220 m elevation) yield ages in the 2.2 to 0.8 Ma interval. Grains of supergene alunite, jarosite, and cryptomelane analyzed from individual single hand specimens yield reproducible results, confirming the suitability of these minerals to 40Ar/ 39Ar geochronology. Multiple samples collected from the same site also yield reproducible results, indicating that the ages measured are true precipitation ages for the samples analyzed. Different sites, up to 3 km apart, sampled from weathering profiles at the same elevation again yield reproducible results. The consistency of results confirms that 40Ar/ 39Ar geochronology of supergene jarosite, alunite, and cryptomelane yields ages of formation of weathering profiles, providing a reliable numerical basis for differentiating and correlating these profiles. The age versus elevation relationship obtained suggest that the stepped landscapes in the Dugald River area record a progressive downward migration of a relatively flat weathering front. The steps in the landscape result from differential erosion of previously weathered bedrock displaying different susceptibility to weathering and contrasting resistance to erosion. Combined, the age versus elevation relationships measured yield a weathering rate of 3.8 m. Myr −1 (for the past 15 Ma) if a descending subhorizontal weathering front is assumed. The results also permit the calculation of the erosion rate of the more easily weathered and eroded lithologies, assuming an initially flat landscape as proposed in models of episodic landscape development. The average erosion rate for the past 15 Ma is 3.3 m. Myr −1, consistent with erosion rates obtained by cosmogenic isotope studies in the region.

Identification of Small Presolar Spinel and Corundum Grains by Isotopic Raster Imaging

AbstractThe oxygen isotopic compositions of densely packed submicron oxide grains in two grain separates of different grain size from the CM2 carbonaceous chondrite Murray were determined by multi-detection raster imaging on the NanoSIMS ion microprobe. This led to the identification of 81 presolar spinel and 3 presolar corundum grains among ∼51 700 grains in the CF residue (mean diameter 0.15 µm) and 171 presolar spinel and 29 presolar corundum grains among ˜21 500 grains in the CG residue (mean diameter 0.45 µm). Previous NanoSIMS analysis of individual grains from the same residues has led to the discovery of 15 presolar spinel and 3 presolar corundum grains among 628 CF grains, and 9 presolar spinels among 753 CG grains. The oxygen isotopic compositions of the presolar oxides found by raster imaging are comparable to those of the presolar oxides measured individually. While the abundance of presolar spinel among the (larger) grains of the CG residue is the same for both techniques, the detection efficiency for presolar spinel by imaging among the (smaller) grains in CF is lower due to the small size of these grains. Nonetheless, it is possible to identify presolar grains of this size range. Though single grain measurements are effective for determining the precise isotopic compositions and abundances of presolar grains, raster ion imaging is the method of choice in searches for rare presolar grain types such as presolar silicates.

Morphologic and magnetic properties of Pd100−xFex nanoparticles prepared by ultrasound assisted electrochemistry

Nanopowdered alloys of Pd100−xFex, with x=4, 6, 8, and 12, have been prepared by ultrasound assisted electrochemistry. The composition of the individual particles, as determined by x-ray fluorescence, and the bulk composition, as determined by atomic absorption, are in agreement within experimental error. Transmission electron microscopy indicates that the nanopowders consist of agglomerates of small grains with a radius of approximately 5 nm, a radius which is confirmed by the broadening of the reflections in the x-ray powder diffraction patterns. X-ray fluorescence analysis of individual grains indicates a homogeneous distribution of palladium and iron throughout the grains. The x-ray diffraction patterns indicate that solid solutions of iron in palladium show no evidence of any pure palladium, any pure iron, or any other PdFe compound. The 78 K iron-57 Mössbauer spectra of these nanopowders reveal the presence of one magnetic sextet assigned to slowly relaxing superparamagnetic particles of Pd100−xFex and one weak doublet, which is assigned to rapidly relaxing superparamagnetic particles of Pd100−xFex. The hyperfine fields of 29.0 to 31.0 T are typical of iron in a metallic alloy and correspond to a magnetic moment of approximately 2 μB per iron atom. The hysteresis curves obtained at 4.2, 100, and 295 K with a vibrating sample magnetometer are typical of superparamagnetic particles with saturation magnetization values which are substantially smaller than those observed for the bulk. The fit of the magnetization curves with a Langevin function yields estimates of the particle radii which are in good agreement with those obtained both by transmission electron microscopy and by the broadening of the x-ray diffraction peaks.

Auriferous mineralization in the Sakoli Group, central India, with particular reference to sulphide-bound gold

Gold mineralization in the Pular-Parsori-Thutanbori belt of the Sakoli Group in central India is hosted predominantly by a felsic volcanic suite of rocks and is associated with quartz-sulphide ±carbonate veins. Both free and submicroscopic or invisible forms of latticebound gold occur. The free gold is found within the shear zone, as either disseminated or fracture-controlled grains within sulphides. Major opaque minerals in this gold-bearing belt include arsenopyrite, pyrrhotite, pyrite, chalcopyrite, sphalerite, galena, molybdenite, magnetite, hematite and scheelite. A three-stage paragenesis been established for these minerals.Mineral chemical analyses of the sulphides reveal the presence of sulphide-bound gold within the belt—the first time such occurrences have been identified in central India. Quantitative spot analyses of individual grains of sulphide indicate high concentrations of lattice-bound gold, which scanning electron micrographs show to be heterogeneously distributed. The substitution of Fe3+ by Au3+ in the lattice structure of the sulphides is postulated as the probable mechanism by which the gold became concentrated.

Degradation of endosperm mRNAs during dry afterripening of cereal grains

AbstractThe endosperm of dormant wild oat (Avena fatuaL.) grains contains a number of mRNAs, including low levels of transcripts encoding avenin (AV10), puroindoline-like (AV1) and serine proteinase inhibitor-like (Z1) proteins. During dry afterripening, a period of warm dry storage that relieves dormancy, the abundance of these intact transcripts gradually declined to undetectable levels in pooled grain samples. In contrast, the three mRNAs did not decline in grains stored for the same period at −20°C, and levels of mRNA decay products derived from these transcripts did not change during afterripening. Disappearance of the three intact mRNAs was not a general phenomenon, since abundance of more than 5000 other seed mRNAs did not change during this period. Additional experiments were conducted to test the idea that the presence of these transcripts was positively correlated with seed dormancy status. First, the rate of intactZ1mRNA decline was similar to the rate of dormancy relief during 9 months of afterripening. Second, cultivated oat (A. sativa) grains (which are not dormant at maturity) contained much lower levels of these mRNAs than did highly dormant wild oat grains. Third, levels of full-lengthAV1andZ1mRNAs remained constant in dormant grains during 6 d of imbibition. However, Northern analyses of individual grains from a partially afterripened seed lot showed that amounts of intactAV1orZ1mRNAs were highly variable in germinating and dormant grains and were not correlated with dormancy status. Even though loss of these transcripts occurred under the same environmental conditions that promote afterripening, a causal relationship between the two processes seems unlikely. The apparently specific mechanism(s) by which these mRNAs are degraded in endosperm tissue may represent a novel post-transcriptional process for regulating levels of certain transcripts in dry grains.

Investigation of structural and catalytic properties of BaLa 4Cu 5−yRu yO 13−δ with 0.0 ≤ y ≤ 3.0 and of LaBaCuRuO 6

We have investigated the possibility of substituting Ru for Cu in the BaLa 4Cu 5O 13−δ structure according the formula BaLa 4Cu 5−yRu yO 13−δ with 0 ≤ y ≤ 3. In the BaLa 4Cu 5O 13−δ structure the solubility of Ru was found to be limited to y < 0.5. For y ≥ 0.5, the samples contained a perovskite-related phase of the composition Ba xLa 4−xCu 2.5Ru 2.5O 13−δ. A monophasic sample was obtained for x = 2.5, with the composition LaBaCuRuO 6, confirmed by X-ray diffraction studies and elemental analysis of individual grains by scanning electron microscopy (SEM). Its structure was determined from X-ray powder diffraction (XRPD) data, using the Rietveld method, and found to be a double-perovskite type with the space group I4/ mand the unit-cell parameters a = 5.6328(1) and c = 7.9877(1). The catalytic activity for simultaneous oxidation of CO and C 3H 6, and reduction of NO was studied over BaLa 4Cu 5O 13−δ, BaLa 4Cu 4.75Ru 0.25O 13−δ, La 4BaCu 2.5Ru 2.5O 13−δ, and LaBaCuRuO 6, under both reducing and oxidizing conditions. BaLa 4Cu 5O 13−δ exhibited some catalytic activity for oxidation of CO and C 3H 6, whereas reduction of NO was found only for the Ru containing samples, and under reducing conditions. The best catalytic activity for oxidation of CO and C 3H 6 and reduction of NO was found for the perovskite-related sample La 4BaCu 2.5Ru 2.5O 13−δ.

Formation of grain-coating chlorite in sandstones. Laboratory synthesized vs. natural occurrences

AbstractGrain-coating chlorites in clastic quartz-rich sandstones have long been recognized as an important porosity-preserving constituent in medium- to deep-burial diagenesis. As little is known about the occurrence and origin of chlorite coatings, chlorite synthesis experiments were performed to study how grain-coating chlorites form in certain sandstones during burial. The starting material was naturally-occuring sandstones from the Oseberg and the Veslefrikk fields offshore Norway, where the same sandstone formation is buried to different depths due to faulting. Grain-coating chlorites exist below ~3000 m burial depth only. At shallower burial (2400 m), an X-ray amorphous iron containing thin clay coating is present.The samples were heated to 200 and 250°C (at water vapour pressure) in a hydrothermal bomb for 2–4 weeks. Both starting material and end-products were studied (electron-) optically in both scanning and transmission microscopes. The TEM showed the Fe-rich precursor material to consist of a fine-grained berthierine-dominated mixed-layer. The neoformed grain coatings in the reacted samples were similar in appearance to naturally-occurring chlorite coatings. The TEM analyses of individual grains documented an Fe-rich chloritic phase with an average composition of Mg0.41Fe3.52Mn0.10Al1.51(Al0.58Si3.42)O10(OH)8. The reacted waters were found to be close to saturation with the newly formed chlorites.Grain-coating chlorite thus appears to form in the natural environment from Fe-rich berthierine precursors at a burial depth corresponding to a temperature around 90°C.