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The water dissolution mechanism in silicate melts under high pressures is not well understood. Here we present the first direct structure investigation of a water-saturated albite melt to monitor the interactions between water and the network structure of silicate melt at the molecular level. In situ high-energy X-ray diffraction was carried out on the NaAlSi3O8-H2O system at 800 °C and 300 MPa, at the Advanced Photon Source synchrotron facility. The analysis of the X-ray diffraction data was augmented with classical Molecular Dynamics simulations of a hydrous albite melt, incorporating accurate water-based interactions. The results show that metal–oxygen bond breaking at the bridging sites occurs overwhelmingly at the Si site upon reaction with H2O, with subsequent Si–OH bond formation and negligible Al–OH formation. Furthermore, we see no evidence for the dissociation of the Al3+ ion from the network structure upon breaking of the Si–O bond in the hydrous albite melt. The results also indicate that the Na+ ion is an active participant in the modifications of the silicate network structure of the albite melt upon water dissolution at high P–T conditions. We do not find evidence for the Na+ ion dissociating from the network structure upon depolymerization and subsequent formation of NaOH complexes. Instead, our results show that the Na+ ion persists as a structure modifier with a shift away from Na–BO bonding to an increase in the extent of Na-NBO bonding, in parallel with pronounced depolymerization of the network. Our MD simulations show that the Si–O and Al–O bond lengths are expanded by about 6% in the hydrous albite melt compared to those of the dry melt at high P–T conditions. The changes in the network silicate structure of a hydrous albite melt at high pressure and temperature, as revealed in this study, must be considered in the advancement of water dissolution models of hydrous granitic (or alkali aluminosilicate) melts. [ABSTRACT FROM AUTHOR]

The first title benzoyl amide, C17H20CINO5 (3a), crystallizes in the monoclinic space group P21/c with Z = 4 and the second, C19H24CINO5 (3b), also crystallizes in P21/c with Z = 8 (Z' = 2), thus there are two independent molecules in the asymmetric unit. In 3a, the phenyl ring makes a dihedral angle of 50.8 (3)° with the amide moiety with the C O group on the same side of the molecule as the C--Cl group. One methoxy group is almost in the plane of the benzene ring, while the ethoxy and other methoxy substituent are arranged on opposite sides of the ring with the ethoxy group occupying the same side of the ring as the C=O group in the amide moiety. For one of the two molecules in 3b, both the amide and 5,5-dimethyl-3-oxocyclohex-1-en-1-yl moieties are disordered over two sets of sites with occupancies of 0.551 (2)/0.449 (2) with the major difference between the two conformers being due to the conformation adopted by the cyclohex-2-en-1-one ring. The three molecules in 3b (i.e., the undisordered molecule and the two disorder components) differ in the arrangement of the subsituents on the phenyl ring and the conformation adopted by their 5,5-dimethyl-3-oxocyclohex-1-en-1-yl moieties. In the crystal of 3a, N--H…O hydrogen bonds link the molecules into a zigzag chain propagating in the [001] direction. For 3b a combination of C--H…O and N--H…O intermolecular interactions link the molecules into a zigzag ribbon propagating in the [001] direction. [ABSTRACT FROM AUTHOR]

The past two decades have witnessed significant advances in the application of X-ray absorption spectroscopy (XAS) to the study of supercritical aqueous fluids. The data obtained usingin situXAS have provided insights into the stability and the structure of metal complexes that are fundamental to understanding natural and industrial hydrothermal processes. Important recent advances using XAS can be attributed to the use of new high temperature and pressure autoclaves designed specifically for the analysis of fluids at extreme temperatures and pressures, improved techniques for the acquisition of X-ray absorption spectra and molecular-level computational modelling used in association with XAS analysis. High-brilliance light sources have not only provided new opportunities for XAS investigations of supercritical fluids, but have also revealed the effects of beam-induced radiolysis of the same fluids. The advent of energy-dispersive and rapid-acquisition XAS holds promise for future studies of beam-induced radiolysis and of the kinetics associated with the formation of metal complexes in high-temperature fluids. [ABSTRACT FROM PUBLISHER]

Diomignite (Li2B4O7) is discredited as a mineral species, and this discreditation has been approved by the International Mineralogical Association, Commission on New Minerals, Nomenclature and Classification. Diomignite was originally reported to occur in virtually every crystal-rich inclusion in spodumene from the Tanco pegmatite in southeastern Manitoba, Canada. However, detailed study of 30 randomly selected crystal-rich inclusions in the purported type material deposited at the U.S. National Museum of Natural History, 30 inclusions in the purported type material from the American Museum of Natural History, and several hundred inclusions in self-collected samples reveals that diomignite is absent in every inclusion examined. Because no holotype specimen exists and no neotype sample was provided by the surviving authors of the original description, the presence of diomignite could not be validated. The evidence provided in the original description to the IMA in 1984 is shown to be insufficient to support the existence of diomignite as a mineral species. The previously reported boron-rich (12 mass% B2O3) composition of the melt represented as crystalrich inclusions in spodumene and petalite from the Tanco pegmatite was predicated on the assumption that diomignite is a common daughter mineral that occurs in most inclusions and that the inclusions are primary melt inclusions. The nonexistence of diomignite, and the absence of other borate daughter minerals, in these crystal-rich inclusions indicates that the boron content was greatly overestimated and so comparisons to experimentally generated boron-rich (>10 mass% B2O3) boundary-layer melts are unwarranted. Furthermore, the discreditation of diomignite negates the inferred role of a Li2B4O7- flux-rich melt in the generation of primary pegmatite textures and rare element oxide mineralization in the Tanco pegmatite. [ABSTRACT FROM AUTHOR]

Aluminum hydroxysulfate, AlSO4(OH), is postulated to play a vital role in controlling the solubility of aluminum in sulfate-rich acidic soils and ground waters, but it has not yet been confirmed in nature. This study reports the synthesis of an AlSO4(OH) crystal at 700 °C and ~1.0 GPa in a hydrothermal diamond-anvil cell from a mixture of 95% H2SO4 and Al2O3 powder and its structure determination from single-crystal X-ray diffraction data. AlSO4(OH) is monoclinic with space group C2/c and unitcell parameters a = 7.1110(4), b = 7.0311(5), c = 7.0088(4) Å, b = 119.281(2)°, and V = 305.65(3) Å ³. Its crystal structure is characterized by kinked chains of corner-sharing AlO6 octahedra that run parallel to the c-axis. These chains are linked together by SO4 tetrahedra and hydrogen bonds, forming an octahedral-tetrahedral framework. Except for the numbers and positions of H atoms, AlSO4(OH) is isostructural with the kieserite-type minerals, a subgroup of the titanite group of minerals. A comparison of powder X-ray diffraction patterns indicates that our AlSO4(OH) is the same as that obtained by Shanks et al. (1981) through hydrolysis of Al2(SO4)3 solutions at temperatures above 310 °C. To date, AlSO4(OH) has been synthesized only at temperatures above 290 °C, implying that it may not stable in low-temperature environments, such as acidic soils and mine waters. The possible environments to find Al(OH)SO4 may include places where sulfur-rich magma-derived fluids react with aluminous rocks under elevated temperature and pressure, and on Venus where a sulfur-rich atmosphere interacts with surface rocks at temperatures above 400 °C. [ABSTRACT FROM AUTHOR]

The pressure in a series of Hydrothermal Diamond Anvil Cell (HDAC) experiments with water plus haplogranite was determined via in-situ observation of the alpha to beta quartz transformation in the range 130–900 MPa and 600–800 °C, by means of laser interferometry. The pressures measured at the alpha-beta quartz transformation temperature are found to be similar or less than the values estimated using the EOS of pure water (including the error) for runs where the transition temperature is ≤ 665 °C. On the contrary, at ~ 780 °C the pressure in the HDAC is ~ 100 MPa greater than that estimated using pure water isochore. A simplified model of haplogranite dissolution in water for an isochoric sample chamber is proposed to explain the negative sign and the variation of the observed discrepancy between measured and calculated pressure. We suggest that, beyond the change in the intrinsic properties of the fluid phase with increasing solute concentration, two factors control the P – T path in the HDAC: (1) hydration of the glass prior to the glass transition; and (2) changing volume of the aqueous pressure medium. The measurements made in this study demonstrate that laser interferometry on quartz inversion is an effective tool for precise pressure determination in HDAC experiments aimed at the investigation of physical and chemical properties of quartz-saturated hydrous melts in the mid and upper continental crust (i.e., P < 1 GPa). [ABSTRACT FROM AUTHOR]

In situhigh-energy X-ray diffraction measurements were made for the first time on a water-saturated silicate melt at high pressure and temperature. A modified hydrothermal diamond anvil cell (HDAC), designed to minimize the path length of the X-ray beam within a diamond anvil and to increase the solid angle of the diffracted beam, was used to reduce high background contributions and extend X-ray diffraction data collection inQspace. Quantitative differential pair distribution function (PDF) analysis of X-ray diffraction data show that the first measurable (Si–O) peak is 0.095 Å greater in length in the hydrous melt than in the starting glass. Contributions from the H2O O–O correlations, as well as from the second nearest neighbor O–O correlations within the silicate melt, are evident within the second peak of the differential PDF. The procedure described opens new opportunities to directly investigate volatile-rich melts at high pressure and temperature. [ABSTRACT FROM AUTHOR]

Abstract: The oxygen fugacity in Hydrothermal Diamond Anvil Cell (HDAC) experiments was determined by means of direct observation of the thermal reduction of molybdite or hematite in water and water–H2O2 solutions. HDAC experiments were conducted with and without rhenium gasket in order to evaluate the effect of rhenium on oxygen fugacity of the contained sample. In experiments where pure water and no Re gasket were used, i.e., when the sample charge is loaded into a laser-drilled recess in the lower anvil, the Log(fO2) was shown to be −19.55±0.13 over a wide range of temperature and pressure conditions (335–500°C, 15.0–136.3MPa — pressure determined using EOS of water by Wagner and Pruss, 2002), i.e., HM+8 to HM−0.5, at the limit temperatures. In contrast, in experiments where a Re gasket was used to contain the sample, the Log(fO2) is slightly more reducing (−20.60±0.04), e.g., equals to HM+6 at 350°C, but is significantly higher than that predicted at a given temperature using the Re–ReO2 buffer. Experiments with hydrogen peroxide showed a non-linear increase of oxygen fugacity with increasing molarity of H2O2 from 0.10 to 0.25M. Results indicate that the oxygen fugacity in water dominated HDAC runs is imposed by the fluid medium, and that hydrogen peroxide may be used to increase oxygen fugacity of water-dominated fluid media in HDAC experiments. [Copyright &y& Elsevier]

Radiolysis-induced effects on aqueous tungsten ions are observed to form a precipitate within seconds upon exposure to a synchrotron X-ray micro-beam in a WO3 + H2O system at 873 K and 200 MPa. In situ Fe K-edge energy-dispersive X-ray absorption spectroscopy (ED-XAS) measurements were made on Fe(II)Cl2 aqueous solutions to 773 K in order to study the kinetics of high-temperature reactions of Fe2+ and Fe3+ ions with transient radiolysis species. The radiolytic reactions in a fluid sample within a hydrothermal diamond anvil cell result in oxidation of the Fe2+ ion at 573 K and reduction of Fe3+ at temperatures between 673 and 773 K and of the Fe2+ ion at 773 K. The edge-energy drift evident in the ED-XAS data directly reflects the kinetics of reactions resulting in oxidation and/or reduction of the Fe2+ and Fe3+ ions in the aqueous solutions at high temperatures. The oxidation and reduction trends are found to be highly consistent, making reliable determinations of reaction kinetics possible. [ABSTRACT FROM AUTHOR]

Abstract: Cathodoluminescence (CL) reveals red and blue colors within single, non-turbid albite (Ab98–99) grains from the Georgeville granite, Nova Scotia. A 720 nm X-ray excited optical luminescence (XEOL) peak characterizes red CL regions, while a 280 nm XEOL feature dominates blue CL regions. Synchrotron X-ray fluorescence results indicate that red CL and the 720 nm XEOL peak intensities relate to total Fe concentrations. The relationship between red CL and Fe content is confirmed by electron microprobe (EMPA) and laser ablation-inductively coupled mass spectrometry (LA-ICP-MS). The XEOL technique is used to exclude the Fe K-edge as the cause of red CL. X-ray absorption spectroscopy results indicate that Fe in both the red and blue CL regions is Fe3+, and that red CL activation may relate to the Si–Al order of the feldspar and to the distribution of Fe on tetrahedral sites. The CL textures, combined with EMPA and LA-ICPMS analyses, indicate that blue CL albite (Ab98) regions contain higher concentrations of Ca, Ti, Pb and rare earth elements, and were replaced, in part, by a more Fe-rich, trace element depleted albite (Ab99) which displays red CL. Complex diffraction contrasts and amorphous deposits identified in transmission electron microscope images suggest that aqueous fluids have reacted with both red and blue CL regions. Fluid inclusion homogenization temperatures of up to 430 °C provide a lower estimate of the fluid temperature. [Copyright &y& Elsevier]

Abstract: Raman analysis of the vapor phase formed after heating pure water to near critical (355–374°C) temperatures in a hydrothermal diamond-anvil cell (HDAC) reveals the synthesis of abiogenic methane. This unexpected result demonstrates the chemical reactivity of diamond at relatively low temperatures. The rate of methane production from the reaction between water and diamond increases with increasing temperature and is enhanced by the presence of a metal gasket (Re, Ir, or Inconel) which is compressed between the diamond anvils to seal the aqueous sample. The minimum detection limit for methane using Raman spectroscopy was determined to be ca. 0.047MPa, indicating that more than 1.4 nanograms (or 8.6×10−11 mol) of methane were produced in the HDAC at 355°C and 30MPa over a period of ten minutes. At temperatures of 650°C and greater, hydrogen and carbon dioxide were detected in addition to methane. The production of abiogenic methane, observed in all HDAC experiments where a gasket was used, necessitates a reexamination of the assumed chemical systems and intensive parameters reported in previous hydrothermal investigations employing diamonds. The results also demonstrate the need to minimize or eliminate the production of methane and other carbonic species in experiments by containing the sample within a HDAC without using a metal gasket. [Copyright &y& Elsevier]

A series of X-ray absorption spectroscopy (XAS) experiments were made to determine the structure and stability of aqueous REE (La, Nd, Gd, and Yb) chloride complexes to 500 °C and 520 MPa. The REE3+ ions exhibit inner-sphere chloroaqua complexation with a steady increase of chloride coordination with increasing temperature in the 150 to 500 °C range. Furthermore, the degree of chloride coordination of REE3+ inner-sphere chloroaqua complexes decreases significantly from light to heavy REE. These results indicate that steric hindrance drives the reduction of chloride coordination of REE3+ inner-sphere chloroaqua complexes from light to heavy REE. This results in greater stability and preferential transport of light REE3+ over heavy REE3+ ions in saline hydrothermal fluids. Accordingly, the preferential mobility of light REE directly influences the relative abundance of REE in rocks and minerals and thus needs to be considered in geochemical modeling of petrogenetic and ore-forming processes affected by chloride-bearing hydrothermal fluids. [ABSTRACT FROM AUTHOR]

Abstract: X-ray absorption spectroscopy (XAS) measurements were made at the Nd L 3-edge on neodymium(III) aqua and chloroaqua complexes in low pH aqueous solutions from 25 to 500 °C and up to 520 MPa. Analysis of the extended X-ray absorption fine structure of the XAS spectra measured from a 0.07 m Nd/0.16 m HNO3 aqueous solution reveals a contraction of the Nd-O distance of the Nd3+ aqua ion at a uniform rate of ~0.013 Å/100 °C and a uniform reduction of the number of coordinated H2O molecules from 10.0±0.9 to 7.4±0.9 over the range from 25 to 500 °C and up to 370 MPa. The rate of reduction of the first-shell water molecules with temperature for Nd3+ (26%) is intermediate between the rate for the Gd3+ aqua ion (22% from 25 to 500 °C) and the rates for the Eu3+ (29% from 25 to 400 °C) and the Yb3+ aqua ions (42% from 25 to 500 °C) indicating an intermediate stability of the Nd3+ aqua ion consistent with the tetrad effect. Nd L 3-edge XAS measurements of 0.05 m NdCl3 aqueous solution at 25 to 500 °C and up to 520 MPa show that stepwise inner-sphere complexes most likely of the type Nd(H2O) δ − n Cl n +3− n occur in the solution at elevated temperatures, where δ ≈9 at 150 °C decreasing to ~6 at 500 °C and the number of chloride ions (n) of the chloroaqua complexes increases uniformly with temperature from 1.2±0.2 to 2.0±0.2 in the solution upon increase of temperature from 150 to 500 °C. Conversely, the number of H2O ligands of Nd(H2O) δ − n Cl n +3− n complexes is uniformly reduced with temperature from 7.5±0.8 to 3.7±0.3 in the aqueous solution, in the same temperature range. These data show greater stability of neodymium(III) than gadolinium(III) and ytterbium(III) chloride complexes in low pH aqueous solutions at elevated temperatures. Our data suggest a greater stability of aqueous light REE than that of heavy REE chloride complexes in low pH fluids at elevated temperatures consistent with REE analysis of fluids from deep-sea hydrothermal vents. [Copyright &y& Elsevier]

A modified hydrothermal diamond anvil cell (HDAC) rail assembly has been constructed for making synchrotron x-ray absorption spectroscopy, x-ray fluorescence, and x-ray mapping measurements on fluids or solid phases in contact with hydrothermal fluids up to ∼900 °C and 700 MPa. The diamond anvils of the HDAC are modified by laser milling grooves or holes, for the reduction of attenuation of incident and fluorescent x rays and sample cavities. The modified HDAC rail assembly has flexibility in design for measurement of light elements at low concentrations or heavy elements at trace levels in the sample and the capability to probe minute individual phases of a multiphase fluid-based system using focused x-ray microbeam. The supporting rail allows for uniform translation of the HDAC, rotation and tilt stages, and a focusing mirror, which is used to illuminate the sample for visual observation using a microscope, relative to the direction of the incident x-ray beam. A structure study of Eu(III) aqua ion behavior in high-temperature aqueous solutions and a study of Nb partitioning and coordination in a silicate melt in contact with a hydrothermal fluid are described as applications utilizing the modified HDAC rail assembly. [ABSTRACT FROM AUTHOR]

Abstract: Synchrotron X-ray spectroscopy experiments were made on the Gd(III) aqua and chloro complexes in low pH aqueous solutions at temperatures ranging from 25 to 500 °C and at pressures up to 480 MPa using a hydrothermal diamond anvil cell. Analysis of fluorescence Gd L3-edge X-ray absorption fine structure (XAFS) spectra measured from a 0.006m Gd/0.16m HNO3 aqueous solution at temperatures up to 500 °C and at pressures up to 260 MPa shows that the Gd–O distance of the Gd3+ aqua ion decreases steadily at a rate of ∼0.007 Å/100 °C whereas the number of coordinated H2O molecules decreases from 9.0±0.5 to 7.0±0.4. The loss of water molecules in the Gd3+ aqua ion inner hydration shell over this temperature range (a 22% reduction) is smaller than exhibited by the Yb3+ aqua ion (42% reduction) indicating that the former is significantly more stable than the later. We conjecture that the anomalous enrichment of Gd reported from measurement of REE concentrations in ocean waters may be attributed to the enhanced stability of the Gd3+ aqua ion relative to other REEs. Gd L3-edge XAFS measurements of 0.006m and 0.1m GdCl3 aqueous solutions at temperatures up to 500 °C and pressures up to 480 MPa reveal that the onset of significant Gd3+–Cl− association occurs around 300 °C. Partially-hydrated stepwise inner-sphere complexes most likely of the type Gd(H2O) δ−n Cl n +3−n occur in the chloride solutions at higher temperatures, where δ ≈8 at 300 °C decreasing slightly to an intermediate value between 7 and 8 upon approaching 500 °C. This is the first direct evidence for the occurrence of partially-hydrated REE Gd (this study) and Yb [Mayanovic, R.A., Jayanetti, S., Anderson, A.J., Bassett, W.A., Chou, I-M., 2002a. The structure of Yb3+ aquo ion and chloro complexes in aqueous solutions at up to 500 °C and 270 MPa. J. Phys. Chem. A 106, 6591–6599.] chloro complexes in hydrothermal solutions. The number of chlorides (n) of the partially-hydrated Gd(III) chloro complexes increases steadily with temperature from 0.4±0.2 to 1.7±0.3 in the 0.006m chloride solution and from 0.9±0.7 to 1.8±0.7 in the 0.1m GdCl3 aqueous solution in the 300–500 °C range. Conversely, the number of H2O ligands of Gd(H2O) δ−n Cl n +3−n complexes decreases steadily from 8.9±0.4 to 5.8±0.7 in the 0.006m GdCl3 aqueous solution and from 9.0±0.5 to 5.3±1.0 in the 0.1m GdCl3 aqueous solution at temperatures from 25 to 500 °C. Analysis of our results shows that the chloride ions partially displace the inner-shell water molecules during Gd(III) complex formation under hydrothermal conditions. The Gd–OH2 bond of the partially-hydrated Gd(III) chloro complexes exhibits slightly smaller rates of length contraction (∼0.005 Å/100 °C) for both solutions. The structural aspects of chloride speciation of Gd(III) as measured from this study and of Yb(III) as measured from our previous experiments are consistent with the solubility of these and other REE in deep-sea hydrothermal fluids. [Copyright &y& Elsevier]

Abstract: Structure–activity relationship studies were employed to synthesize a series of 3- and 3,4-substituted benzamides from 3-amino-2-cyclohexenones. An improved method for the synthesis of benzamides from 3-amino-2-cyclohexenones is presented which provided significantly higher yields (71–79%) for the reported compounds. NMR and X-ray structural analyses were undertaken to note the possible intra- and intermolecular interactions of the synthesized analogs. Molecular modeling studies were used to determine the minimized configuration and were compared to their X-ray structures for correlation. These new entities were evaluated as potential anticonvulsants and type IV phosphodiesterase inhibitors (PDE4). [Copyright &y& Elsevier]

Presents a study that investigated the hydration structure of lanthanum (La) ion in aqueous nitrate solutions in a hydrothermal diamond anvil cell. Use of X-ray absorption fine structure (XAFS) technique; Analysis of XAFS data; Comparison of results with previous studies of La hydration at room temperature.

Describes an adaptation of the spindle stage for geometric analysis of fluid inclusions. Three-dimensional observation of fluid inclusions; Fluid inclusion phase ratios; Paleo-fracture analysis; Quantitative microanalysis; Evaluation of decrepitation behavior.

Presents a study on organic-walled fossils, such as graptolites and Chitinozoa. Methodology employed in this study; Use of infrared video microscopy (IVM) to provide real-time images of the three-dimensional form and internal structure of many specimens that are opaque to visible light; Results of study.

This article presents a set of technical and instructional strategies for the effective implementation of desktop video-assisted teaching and learning. It is noted that further advances in desktop video technology are likely to herald new application possibilities.

Critical aspects of the crystallization dynamics of H2O-saturated melts of a typical granitic composition as well as granitic melts enriched in lithium (8800 ppm) were investigated in real-time experiments using the hydrothermal diamond anvil cell at 480-700 °C and 220-960 MPa. Complete crystallization of the charges was achieved within 5-118 h with average crystal growth rates ranging from 3 to 41 cm/year for quartz and from 18 to 58 cm/year for alkali feldspars, demonstrating that crystals formed from a silicate melt in the presence of a coexisting aqueous phase crystallize rapidly. The combination of substantial nucleation delays, low nucleation densities, and rapid growth rates for quartz and alkali feldspars led to the formation of euhedral megacrysts of these minerals in the vicinity of clusters comprised of much smaller muscovite or α-spodumene crystals. Subsolidus replacement processes initiated during crystal-fluid interactions after the silicate melt was consumed were directly observed in the experiments. The experimental results underscore the important role of water as a medium for the transport of essential elements such as Si, Al, Na, and K from the silicate melt to the newly formed crystals, and provide important insights into the crystallization of miarolitic pegmatites. [ABSTRACT FROM AUTHOR]

Our previous x-ray absorption fine structure studies of aqueous solutions revealed relaxation of the structure of complexes of Zn[sup 2+], Fe[sup 2+], La[sup 3+], and Yb[sup 3 +] ions with increasing temperature. These complexes in general exhibit reduction of cation-ligand bond lengths with increasing temperature due to hydrogen bond breaking and loss of water of solvation. Because this results in an overall lowering of the equilibrium state of the complex, we refer to the variation of the structure as relaxation. In the case of M(H[sub 2]O)[sup n+, sub m] (m = 6-9 at room temperature, n = 2, 3) aquo ion complexes (M: Zn, Fe, La, Yb), there is a similar reduction in the number of coordinating water molecules with temperature. The relaxation of the structure is shown to result in a lowering of the binding energy per cation-ligand pair of a complex with increasing temperature. A comparison of the rate of structure relaxation with temperature, which is framed in the context of volume thermoelastic constriction, shows this quantity to have a gradual and direct dependence on the difference in Pauling's electronegativity of the cation-ligand pairs making up the ion complex. [ABSTRACT FROM AUTHOR]

The late Proterozoic Georgeville Granite is an A-type granite situated about 20 km north of Antigonish, Nova Scotia. The bulk granite composition is characterized by high SiO2, Th, Nb, Y and Zr and low CaO, TiO2, MgO, FeO and MnO. Cathodoluminescence (CL) images, obtained from several thin sections of the granite, show that most feldspars display red luminescence. However, the inner regions of some plagioclase grains display a blue colour. These grains with blue inner regions and red rims are optically continuous and show no obvious signs of alteration when observed with a petrographic microscope. Previous studies of feldspars in other igneous intrusions have attributed the red CL colour to the presence of ferric iron introduced by late-stage fluids. In order to understand the metasomatic modification of the feldspars in the Georgeville Granite, the structure and chemistry of the red and blue CL regions was characterized using X-ray Excited Optical Luminescence (XEOL), X-Ray Absorption Spectroscopy (XAS), Synchrotron X-Ray Fluorescence (SRXF) and electron microprobe analyses. The XEOL results show that blue CL is strongly correlated with a UV feature at ca. 290 nm, and red CL is strongly correlated with an IR feature at ca. 720 nm. Both the 290 and 720 nm features are visible when the XEOL source was tuned below the excitation energy of the Fe K-edge. Using the XEOL spectra as a guide, XAS and SXRF spectra were recorded from red and blue CL regions. The XAS spectra indicate no change in either the coordination or the valance state of Fe between the red and blue CL regions. The SXRF data show that the red CL regions have higher concentrations of Fe3+ and Mn and lower Ca, Ti, and K than the blue CL regions. The blue CL regions within individual grains may therefore represent relicts of original plagioclase. Fe3+-enriched metasomatic albite is wide spread and readily identified by red CL. [ABSTRACT FROM AUTHOR]

The Greenbushes rare-element pegmatite, Western Australia, is currently mined for lithium and tantalum and is among the largest tantalum producers in the world. Although tantalite is the dominant ore mineral, more than ten other tantalum-bearing phases have been reported. The tantalum-rich pyrochlore, microlite, has been identified in mill concentrates at the Greenbushes mine, however its paragenesis is not well documented. In the present petrographic investigation of different zones within the Greenbushes pegmatite, microlite was discovered within a fine grained assemblage of quartz, albite and fluorapatite in the border zone near the footwall contact of the pegmatite. It occurs as equant, anhedral to subhedral grains that are generally less that 0.5 mm in diameter. The grains are pale yellow in plane polarized light and sometimes contain small inclusions of a high birefringence mineral. Optical and backscattered electron images (BSEI) indicate that most individual grains are essentially homogeneous in composition and texture. Raman spectra obtained from Greenbushes microlite closely matches that of stannomicrolite, but electron microprobe results reveal significant concentrations of antimony in addition to tin. Microlite occurs in intensely sheared and recrystallized pegmatite; however, individual grains show no sign of deformation or alteration. We suggest that microlite precipitation is coeval with late deformation and the remobilization of tantalum within the pegmatite. The occurrence of microlite and abundant apatite in the border zone is attributed in part to chemical exchange between the pegmatite and the calcium-rich metasedimentary host rocks. [ABSTRACT FROM AUTHOR]

A Raman spectral study was carried out on three aqueous solutions of varying concentration and bromide/zinc ratio. Spectra were collected at 11 different temperature-pressure conditions ranging from ambient to 500°C and up to 0.9 GPa. Raman band assignments for aqueous zinc bromide complex species reported in previous studies were used to determine the relative concentrations of ZnBr42-, ZnBr-3 , ZnBr2, and ZnBr+ species at various temperatures and pressures. Our results are in close agreement with X-ray absorption spectroscopic (XAS) data, and confirm that the tetrabromo zinc complex, ZnBr42-, is the predominant species up to 500°C in solutions having high zinc concentrations (1 m) and high bromide/zinc molar ratios ([Br]/[Zn] = 8). This result is consistent with the observed predominance of the ZnCl42- 4 , complex in chloriderich fluid inclusion brines at high temperatures. In agreement with previous solubility and Raman spectroscopic experiments, our measurements also indicate that species with a lower number of halide ligands and charge are favored with increasing temperature in dilute solutions, and solutions with low bromine/zinc ratios ([Br]/[Zn] < 2.5). Raman and X-ray absorption spectroscopy are complementary techniques that were used in this study to obtain speciation and structural data on aqueous zinc bromide solutions at elevated temperatures and pressures. Furthermore, we show that Raman spectroscopy, in some cases, may be used to independently evaluate XAS data obtained from high temperature disordered systems such as supercritical fluids. [ABSTRACT FROM AUTHOR]

Abstract: In situ Ta L 3-edge XAS measurements have been made from a Ta (~1400ppm)-bearing peraluminous silicate glass+H2O system to 960°C and ~0.6GPa. A white-line doublet separated by ~4eV occurs in the Ta L 3-edge XANES and results from octahedral crystal field splitting of the Ta 5d levels due to the local structure surrounding Ta coordinated by Qn-species (n=number of bridging oxygen atoms shared between SiO4 and AlO4 units) in the silicate glass/melt+H2O system. The XANES spectra measured from the hydrous silicate glass/melt and from the silicate-rich aqueous fluid have been analyzed using multi-peak fitting techniques. The white-line doublet intensity varies with increasing P–T conditions of the silicate glass/melt+water system, indicating a shift in the electronic density of states in the vicinity of quasi bound Ta 5d states probed by the 2p3/2 core photoelectron. Ab initio modeling of the XANES indicates that water dissolution causes distortion of local structure surrounding the 6-fold coordinated Ta–Qn clusters in the hydrous silicate glass/melt and in the silicate-rich aqueous fluid. Calculation of the angular-momentum projected density of states (l-DOS) shows that the upper doublet level quasi-bound d-DOS is steadily reduced with increasing distortion of the local structure surrounding Ta–Qn clusters. [Copyright &y& Elsevier]

Abstract: A Raman spectral study was carried out on 3 solutions of varying concentration and bromide/zinc ratios. Spectra were collected at 11 different temperature–pressure conditions ranging from ambient to 500 °C–0.9 GPa. Raman band assignments for zinc(II) bromide species reported in previous studies were used to determine the relative concentrations of ZnBr4 2−, ZnBr3 −, ZnBr2, and ZnBr+ species at various temperatures and pressures. Our results are in close agreement with X-ray absorption spectroscopic (XAS) data, and confirm that the tetrabromo zinc(II) complex, ZnBr4 2−, is the predominant species up to 500 °C in solutions having high Zn concentrations (1 m) and high bromide/zinc molar ratios ([Br]/[Zn]=8). In agreement with previous solubility and Raman spectroscopic experiments, our measurements indicate that species with a lower number of halide ligands and charge are favored with increasing temperature in dilute solutions, and solutions with low bromide/zinc ratios ([Br]/[Zn] <2.5). The Raman technique provides an independent experimental means of evaluating the quality of XAS analyses of data obtained from high temperature disordered systems. The combination of these two techniques provides complementary data on speciation and the structure of zinc(II) bromide complexes. The preponderance of the ZnBr4 2− species in highly saline brines at high temperature is consistent with the predominance of ZnCl4 2 − in chloride-rich brines reported in previous XAS studies. Knowledge of Zn complexing in metal-rich highly saline brines is important for numerical models of ore deposition in high temperature systems such as skarns and porphyry-type deposits. [Copyright &y& Elsevier]

Metal gaskets (Re, Ir, Inconel, or stainless steel) normally used to contain fluid samples in the hydrothermal diamond-anvil cell (HDAC) are sometimes undesirable due to possible contamination and to gasket deformation at high pressures and temperatures resulting in nonisochoric behavior. Furthermore, in x-ray spectroscopic experiments, metal gaskets may attenuate the incident x-ray beam and emitted fluorescence x-rays, and the interaction of scattered radiation with the gasket may produce fluorescence that interferes with the x-ray spectrum of the sample. New arrangements and procedures were tested for the operation of the HDAC without using the metal gaskets. Distilled, de-ionized water was loaded into the sample chamber, a laser-milled recess 300 μm in diameter and ∼50 μm deep centered in the 1.0 mm face of the lower diamond anvil, and sealed by pressing the top diamond anvil face directly against the lower one without a metal gasket in between. A maximum sample pressure of 202 MPa at 617 °C was maintained for a duration of 10 min without evidence of leakage. A small change in fluid density was observed in one experiment where the sample was held at 266 MPa at 708 °C for 10 min. The gasketless HDAC was also employed in x-ray absorption spectroscopy experiments, where, in addition to the sample chamber in the lower diamond, two grooves were milled at a 90° angle to each other around the sample chamber to minimize the attenuation of incident and fluorescent x rays. With a minimum distance between the sample chamber and the grooves of 80 μm, a pressure of 76 MPa at 500 °C was maintained for 2 h with no change in the original fluid density. [ABSTRACT FROM AUTHOR]

Abstract: In situ XRF and Mo K-edge XAS measurements were made on the ID20-B beam line at the APS on MoO3 in 1M H2O2 aqueous solution, at temperatures between 400 and 600°C. The samples were analyzed using a modified Bassett-type hydrothermal diamond anvil cell. Our XRF measurements show that MoO3 is highly soluble in the supercritical H2O2 aqueous fluid. Analysis of XAS spectra shows that the Mo6+ ion exhibits consistent speciation in the H2O2 aqueous solution at temperatures ranging from 400 to 600°C. [Copyright &y& Elsevier]

The article discusses the synthesis of the proposed structure of kedarcidin chromophore, a component of the cytotoxic protein, and the evidence for its stereochemical revision. According to the authors, their spectroscopic data reveal that the structure of kedarcidin chromophore must be revised. They claim that the revised structure is consistent with its chemical shift and its coupling constant values.

Synchrotron x-ray radiation is being used extensively as a structure probe to investigate the coordination environment and thus gain insight into the ion–water and ion–ion interactions in aqueous solutions. However, under favorable conditions, there may be instances where the incident x-ray beam can induce oxidation and/or reduction in the solution, thus altering its chemistry. Successive x-ray absorption fine structure spectra, measured in the fluorescence mode from a 55 ppm Cu in CuCl[sub 2] aqueous solution, show the formation of copper clusters and their growth as a function of time of irradiation. Initially, the clusters have a nearest neighbor distance of 2.48±0.02 Å which, with increase in time of irradiation, increases to 2.55±0.01 Å, indicating that the clusters approach the lattice dimensions of bulk copper. Similarly, the Debye–Waller factor of the copper clusters is found to increase by ∼50%–55% over the range of time of irradiation. Analysis of spectra measured in the intermediate time period shows signal contributions from a mixture of clusters that can be represented by a mixture of a small cluster (5–10 Å across) and bulk copper. The nearest neighbor coordination number is found to increase in a manner consistent with the decrease in the surface to volume ratio as the average cluster size approaches its bulk dimensions. The initiation of cluster growth occurs through agglomeration of copper atoms that possibly react to form dimers upon reaction. The copper ions in the solution are reduced to the metallic state by reacting with hydrated electrons produced as a result of radiolysis of water by the incident x-ray beam. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Highlights: [⿢] Co2+ ion adsorption on Fe3O4 nanoparticles in hydrothermal fluids was measured in situ. [⿢] In situ measurements allowed direct study of the nanoparticle⿿fluid interface. [⿢] In situ XAS shows that Co2+ adsorbs on octahedral sites of Fe3O4 NPs from 250°C to 500̿C. [⿢] This work has relevance to corrosion issues in supercritical water cooled reactors. [ABSTRACT FROM AUTHOR]

Symmetrical and unsymmetrical 3-halo- or 3-methoxy- substituted 2-dibenzoylamino- 1,4-naphthoquinone analogs were synthesized with an average yield of 45% via sodium hydride promoted bis-acylation of 2-amino-3-chloro-1,4-naphthoquinone, 2-amino-3-bromo- 1,4-naphthoquinone and 2-amino-3-methoxy-1,4-naphthoquinone. [ABSTRACT FROM AUTHOR]