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  • 1
    Electronic Resource
    Electronic Resource
    Proton environments and hydrogen-bonding in hydrous silicate glasses from proton NMR (1989)
    [s.l.] : Nature Publishing Group
    Nature 337 (1989), S. 539-541 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The proton magic-angle-spinning (MAS) NMR spectrum for sample SIC, an SiO2 glass containing 2.5 wt% water quenched from 1,320°C and 1 kbar (Fig. \b) consists of an asymmetric peak, broadened towards high frequency. Although this could be explained in terms of a distribution of proton ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/337539a0
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  • 2
    Electronic Resource
    Electronic Resource
    Structural relations and tetrahedral ordering pattern of synthetic orthorhombic Cs2CdSi5O12 leucite: a combined synchrotron X-ray powder diffraction and multinuclear MAS NMR study (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 560-566 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768194003393
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  • 3
    Electronic Resource
    Electronic Resource
    Structures of synthetic K2MgSi5O12 leucites by integrated X-ray powder diffraction, electron diffraction and 29Si MAS NMR methods (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 31-41 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768193008754
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  • 4
    Electronic Resource
    Electronic Resource
    The structural environments of trace elements in dry and hydrous silicate glasses; a manganese and strontium K-edge X-ray absorption spectroscopic study (1990)
    Springer
    Contributions to mineralogy and petrology 105 (1990), S. 359-368 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The structural environments of Mn2+ and Sr2+ at concentrations of 0.2–0.8 wt% in dry and hydrous silicate glasses have been studied using X-ray absorption spectroscopy (EXAFS and XANES). The environment of Mn in hydrous silica glasses containing 4.5 and 6.0 wt% H2O appears to be close to an undistorted octahedral site, whereas Mn in other compositions, both dry and hydrous, occupies either a distribution of octahedral and tetrahedral sites, or distorted, non-centrosymmetric sites. The fraction of non-centrosymmetric sites (including tetrahedral) or the average degree of distortion of the sites decreases with both increasing dissolved water concentration and number of non-bridging oxygens in the glass. For Sr the changes as a function of polymerisation and water concentration are less clear, but it appears that the average Sr-O distances are shorter than in crystalline silicates and decrease further with decreasing polymerisation. The structural data obtained in this study are not readily integrated with previous partitioning data for Mn, suggesting that changes in the first-shell coordination geometry of Mn do not play a direct role in controlling the melt compositional dependence of trace element partition coefficients. It is tentatively suggested that distortions of the framework resulting from the incorporation of Mn (i.e. a second shell effect) control the partitioning behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00306545
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  • 5
    Electronic Resource
    Electronic Resource
    Element zoning trends in olivine phenocrysts from a supposed primary high-magnesian andesite: an electron- and ion-microprobe study (1989)
    Springer
    Contributions to mineralogy and petrology 103 (1989), S. 242-252 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Electron and ion-probe microanalysis have been used to obtain zoning profiles for major and trace elements in olivine phenocrysts from a high-magnesian andesite from Shodo-Shima island, southwest Japan. This rock was previously thought to represent undifferentiated, primary magma. Some crystals have unzoned cores, while others show cores which are reversely zoned with respect to Mg/ (Mg+Fe), Ni, Mn and Cr. In addition, some Ni profiles show a normally zoned “hump” at the most central portions of the reversely zoned crystals. All crystals show normally zoned rims. The Li concentrations are constant throughout the cores of all crystals studied, but rise sharply, by a factor of up to at least six, in the rims. The Ca and Co concentrations are essentially constant throughout all the crystals. Mechanisms for producing the observed zoning profiles are discussed, and it is concluded that the reverse zoning was produced by the introduction of crystals into a less differentiated magma than that in which they grew. The reversely zoned crystals could therefore represent xenocrysts which were introduced into an undifferentiated magma, or phenocrysts introduced into a more primitive magma by a magma mixing process. The Ni profiles are used to estimate the residence time of these crystals in the more primitive magma. The following trace element partition co-efficients have been estimated for the olivine-groundmass system in this rock: D Ni=16; D Mn=1.1; D Co=4.2; D Ca =0.02; D Ti=0.005; D V=0.05; D Sc=0.2; D Na=0.0002. Studies of trace element zoning will become increasingly important as the new generation of trace element microprobes become available but a larger database of experimentally determined values for trace element partition coefficients and diffusion coefficients in crystals and magmas, and a better understanding of other disequilibrium processes are required to fully exploit the new data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378510
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  • 6
    Electronic Resource
    Electronic Resource
    An NMR study of structure and ordering in synthetic K2MgSi5O12, a leucite analogue (1991)
    Springer
    Physics and chemistry of minerals 18 (1991), S. 144-152 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Phases with the composition K2MgSi5O12, belonging to the leucite structure group were synthesised under dry and hydrothermal conditions and studied using 29Si NMR. The 29Si spectrum for the dry-crystallised material (which is cubic) consists of a single broad line, suggesting a high degree of disorder. The hydrothermally crystallised material (which is probably monoclinic, with a distorted leucite lattice) has a 29Si spectrum which consists of ten lines of equal intensity, two of which have small chemical shift anisotropies and are therefore assigned to Q4(4Si) sites. These data have been interpreted in terms of a structure with 12 distinct tetrahedral sites over which 2 Mg atoms and 10 Si atoms are fully ordered. A 2-dimensional COSY spectrum shows correlations between some Q4(3Si) silicon atoms and two other Q4(3Si) silicon atoms. This fully constrains the topology of the unit cell. Two schemes of Si/Mg ordering over the unit cell can give good fits to the COSY spectrum. Using the tetrahedral (T) site notation defined for natural tetragonal leucite, the first of these arrangements involves Mg and Q4(4Si) silicon atoms each occupying one T1-type site and one T3-type site, and Q4(3Si) silicons occupying the remaining sites, i.e. four T2-type sites, two T1-type sites and two T3-type sites. In the second arrangement, the T2-type sites are occupied by Mg atoms and Q4(4Si) silicon atoms and all the T1-and T3-type sites are occupied by Q4(3Si) atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00216607
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  • 7
    Electronic Resource
    Electronic Resource
    NMR studies of the leucite analogues X2YSi5O12, where X= K, Rb, Cs; Y = Mg, Zn, Cd (1994)
    Springer
    Physics and chemistry of minerals 21 (1994), S. 176-190 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract A number of leucite group materials with the formula X2YSi5O12 where X=K, Rb, Cs and Y=Mg, Zn, Cd have been synthesized by dry and hydrothermal crystallization of glass starting materials. 29Si MASNMR has been used to obtain structural information, such as the number of distinct tetrahedral sites, degree of cation ordering, and estimates of the mean T-O-T bond angles of the tetrahedra. X-ray powder diffraction gave information on cell volumes and degree of distortion from cubic symmetry for all the samples and space group and structural information for some samples. Integration of the different length-scale data obtained using these two complementary techniques allows greater reliance to be placed on the structures deduced for these leucite samples, which are only available as fine-grained powders. Hydrothermally synthesized K2MgSi5O12, K2ZnSi5O12 and Rb2ZnSi5O12 have structures with 12 distinct tetrahedral sites (T-sites) and are monoclinic P21/c while the dry-synthesized equivalents are disordered with single T-sites and are cubic, Ia3d. Most of the other members of the group have structures with 6 tetrahedral sites with Cs2CdSi5O12 being orthorhombic, Pbca. Cs2ZnSi5O12 has an intermediate “5+2” structure. Decreasing the size of the X+ cation for a given Y2+ cation gives more collapsed and distorted frameworks. 133Cs NMR was used to show that samples with 6 T-sites have 2 alkali sites. It is deduced that samples with 12 T-sites will undergo a displacive phase transition to a 6 T-site structure (possibly via a 5+2 intermediate in some cases) with no change in the framework topology or degree of T-site ordering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203148
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  • 8
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    Phosphorus partitioning between olivine and melt: An experimental study in the system Mg2SiO4-Ca2Al2Si2O9-NaAlSi3O8-Mg3(PO4)2 (2013)
    Mineralogical Society of America
    Details
    Publication Date: 2013-10-02
    Description: The partitioning of phosphorus between olivine and melt was measured by conducting partitioning experiments within the system Mg 2 SiO 4 -Ca 2 Al 2 Si 2 O 9 -NaAlSi 3 O 8 -Mg 3 (PO 4 ) 2 , using olivines crystallized with cooling rates in the range 1 to 10 ºC/h. Partition coefficients, D P ol/melt , vary from 0.05 to 1.41 and are strongly influenced by melt composition, with high partition coefficients observed for more polymerized melts. Correlations between elemental abundances in the olivines demonstrate that phosphorus substitutes on a near one for one basis for Si, charge-balanced by Mg vacancies; no correlation between P and Al concentration in the olivine was observed. A complete understanding of the controls on D P ol/melt is required to model quantitatively the zoning of P in olivine that has recently been shown to be a common feature of igneous olivine crystals. The strong melt compositional dependence observed in this study implies that both changing concentrations of P in the melt during fractionation, and changing values of D P ol/melt can contribute to core-to-rim variations in P when the surface composition of a growing olivine crystal is in equilibrium with the melt. The common observation of zones in natural olivines where high P is correlated with high Al and Cr must be explained by processes other than equilibrium growth and, as suggested previously, such zones are probably related to solute trapping during episodes of rapid growth.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 9
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    Identification of hydrogen defects linked to boron substitution in synthetic forsterite and natural olivine (2014)
    Mineralogical Society of America
    Details
    Publication Date: 2014-10-02
    Description: Experimental and theoretical evidence for the coupled substitution of B and H in synthetic forsterite and a natural olivine is presented. The intensities of OH bands at 3704 cm –1 (//z), 3598 cm –1 (//x,y), and 3525 cm –1 (//x) in a heterogeneous B-doped synthetic forsterite crystal matches the zoning of B concentration measured by ion probe. The two anti-symmetric stretching vibrations of BO 3 groups occur at 1301 cm –1 (//x) and 1207 cm –1 (//z) for the 10 B and at 1256 and 1168 cm –1 for the 11 B isotope. A microscopic model of the mixed (B,H) defect that accounts for experimental observations is obtained from quantum mechanical calculations. The BO 3 group lies on the (O3-O1-O3) face of the vacant Si site and the H atom is bonded to the O2 atom at the remaining apex. The occurrence of the same OH bands associated with 3 BO 3 vibrations in a natural olivine sample from Pakistan confirms the occurrence of this defect in nature. The three diagnostic OH bands can be used as a signature of H associated with boron substitution in olivine and forsterite, leading to a quantitative analysis of their contribution to H-defects.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 10
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    Experimental Simulation of Closed-System Degassing in the System Basalt-H2O-CO2-S-Cl (2011)
    Oxford University Press
    Details
    Publication Date: 2011-08-21
    Description: Magma degassing processes are commonly elucidated by studies of melt inclusions in erupted phenocrysts and measurements of gas discharge at volcanic vents, allied to experimentally constrained models of volatile solubility. Here we develop an alternative experimental approach aimed at directly simulating decompression-driven, closed-system degassing of basaltic magma in equilibrium with an H–C–O–S–Cl fluid under oxidized conditions (f O2 of 1·0–2·4 log units above the Ni–NiO buffer). Synthetic experimental starting materials were based on basaltic magmas erupted at the persistently degassing volcanoes of Stromboli (Italy) and Masaya (Nicaragua) with an initial volatile inventory matched to the most undegassed melt inclusions from each volcano. Experiments were run at 25–400 MPa under super-liquidus conditions (1150°C). Run product glasses and starting materials were analysed by electron microprobe, secondary ion mass spectrometry, Fourier transform infrared spectroscopy, Karl-Fischer titration, Fe 2+ /Fe 3+ colorimetry and CS analyser. The composition of the exsolved vapour in each run was determined by mass balance. Our results show that H 2 O/CO 2 ratios increase systematically with decreasing pressure, whereas CO 2 /S ratios attain a maximum at pressures of 100–300 MPa. S is preferentially released over Cl at low pressures, leading to a sharp increase in vapour S/Cl ratios and a sharp drop in the S/Cl ratios of glasses. This accords with published measurements of volatile concentrations in melt inclusion and groundmass glasses at Stromboli (and Etna). Experiments with different S abundances show that the H 2 O and CO 2 contents of the melt at fluid saturation are not affected. The CO 2 solubility in experiments using both sets of starting materials is well matched to calculated solubilities using published models. Models consistently overestimate H 2 O solubilities for the Stromboli-like composition, leading to calculated vapour compositions that are more CO 2 -rich and calculated degassing trajectories that are more strongly curved than observed in experiments. The difference is less acute for the Masaya-like composition, emphasizing the important compositional dependence of solubility and melt–vapour partitioning. Our novel experimental method can be readily extended to other bulk compositions.
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
    Published by Oxford University Press
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