Journal of Mineralogical and Petrological Sciences
Online ISSN : 1349-3825
Print ISSN : 1345-6296
ISSN-L : 1345-6296
Volume 113 , Issue 6
December
Showing 1-9 articles out of 9 articles from the selected issue
ORIGINAL ARTICLES
  • Hiroshi ARIMA, Yuki TANI, Kazumasa SUGIYAMA, Akira YOSHIASA
    2018 Volume 113 Issue 6 Pages 273-279
    Published: 2018
    Released: December 29, 2018
    [Advance publication] Released: December 11, 2018
    JOURNALS FREE ACCESS

    Local structural features around Mn and Fe in Mn–bearing andalusite from Västanåberget, Sweden were investigated by anomalous X–ray scattering (AXS) and X–ray absorption fine structure (XAFS). The X–ray absorption near edge structure (XANES) spectra indicate that all of the Mn and Fe atoms are in +3 oxidation state. Both the electron density map of Mn obtained by AXS and simulated multiple–scattering extended X–ray absorption fine structure (EXAFS) spectra indicate that the Mn atoms exclusively occupy Al1 sites. Further, the EXAFS analysis indicates that the first neighbor coordinated to Mn at the Al1 site shows a complete structural relaxation and Jahn–Teller distortion owing to Mn3+. In addition, the EXAFS analyses reveal that Fe occupies both Al1 and Al2 sites. The Fe site occupancy ratio (Fe at Al2 to total Fe) in the Mn–bearing andalusite sample is 40–50%. Employing the local structural information around Mn and Fe, a conventional single–crystal structural refinement converged at R = 2.34% with a structural formula of (Al0.82Mn0.16Fe0.02)[6](Al0.99Fe0.01)[5]SiO5 (space group Pnnm with a = 7.8538(9), b = 7.9463(9), c = 5.5867(6) Å).

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  • Akihiko NAKATSUKA, Akira YOSHIASA, Keiko FUJIWARA, Osamu OHTAKA
    2018 Volume 113 Issue 6 Pages 280-285
    Published: 2018
    Released: December 29, 2018
    [Advance publication] Released: December 14, 2018
    JOURNALS FREE ACCESS

    Single–crystal X–ray diffraction analysis of a high–pressure cubic perovskite SrGeO3 was conducted for a temperature range of 100 to 473 K. The crystal structure begins to deteriorate at a temperature higher than 323 K and completely amorphizes by 448 K. Structure refinements in a range of 100 to 323 K show that the displacement ellipsoid of the O atom is considerably suppressed in the direction of the Ge–O bond and that its mean square displacement (MSD) in this direction is almost temperature–independent. In contrast, that in the direction perpendicular to the bond largely increases with the temperature. The Debye temperatures for each constituent atom were determined by applying the Debye model to the temperature dependence of its MSDs. The one–particle potential (OPP) coefficient evaluated from the resulting Debye temperature of the Ge atom is significantly larger than those of the Sr and O atoms. Moreover, the OPP coefficients of the O atom are significantly larger in the direction of the Ge–O bond than in the directions perpendicular to the bond. These results are concordant with our previous finding that the Ge–O bond is largely covalent. The high covalency can have a large influence on the temperature dependence of the thermal vibration of the O atom.

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  • Tomonori OHASHI, Tatsuya SAKAMAKI, Ken–ichi FUNAKOSHI, Akio SUZUKI
    2018 Volume 113 Issue 6 Pages 286-292
    Published: 2018
    Released: December 29, 2018
    [Advance publication] Released: December 18, 2018
    JOURNALS FREE ACCESS

    The structural determinations of basaltic glass under pressure were conducted. The obtained structure factor, S(Q) indicates that the position of the first sharp diffraction peak (FSDP) shifts to higher–Q region with increasing pressure up to 6 GPa. This result indicates the intermediate–range order structure of glass becomes compact. The radial distribution function, RDF shows the shrinkage of the average T–T length with increasing pressure, but indicates no detectable change of the average T–O length (T = Si4+ and Al3+) and its coordination. This result implies that the positional shift of the FSDP is attributed to the polymerization of TO4 tetrahedra to form …–T–O–T–… linkage, with the concomitant narrowing of the mean T–O–T angle. The RDF also shows that the distances of Fe(Mg)–O extend due to the changes in the structural roles of Fe and Mg from the network modifiers to the charge–balancing cations. The structural data of the recovered condition imply that the tetrahedral networks of the present glass is permanently polymerized and densified after compression. On the other hand, the network modifier cations undergo both contraction and relaxation processes.

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  • Euis T. YUNINGSIH, Hiroharu MATSUEDA, Ildrem SYAFRIE
    2018 Volume 113 Issue 6 Pages 293-309
    Published: 2018
    Released: December 29, 2018
    [Advance publication] Released: December 14, 2018
    JOURNALS FREE ACCESS

    Tellurium–bearing gold, silver, and base metal assemblages characterize the epithermal mineralization in southwestern Hokkaido, Japan. The telluride deposits in this district consist of quartz–filled fracture systems of Late Miocene to Pliocene age. Most of the telluride mineralization in southwestern Hokkaido consists of vein systems or are massive in form. The dominant host rocks for this deposit type are intermediate to acid volcanic rocks. The gangue and alteration minerals are very fine to fine–grained quartz, chalcedony, anatase, zeolite, sericite, barite, adularia, chlorite, smectite or other clay mineral, while carbonate (calcite and rhodocrosite) and Mn minerals are poorly represented and rarely coexist with tellurides. The country rocks suffered argillic and propylitic alterations, silicification, and kaolinitization. Tellurium–bearing mineralization is related to or co–exists with sulfide and sulfosalt mineralization. The tellurides identified in the studied area consist of native tellurium, hessite, stutzite, petzite, sylvanite, calaverite, tellurobismuthite, tetradymite, Se–bearing tetradymite, tellurantimony, goldfieldite, altaite, coloradoite, tellurite, teineite, and poughite. The first crystallized telluride minerals such as native tellurium, stutzite, petzite, sylvanite and hessite are followed by calaverite, coloradoite, tellurobismuthite, tellurantimony, and altaite, indicating a decline in tellurium activity during telluride deposition with time. Microthermometry of fluid inclusions in quartz and barite indicate that the mineralization formed at moderate temperatures, ranging from 250–200 °C with low average salinity (1.9–5.7 wt% NaClequiv.). The shift in mineralogy reflects decreases in temperature and fugacity of sulfur, with a concomitant increase in fugacity of tellurium. Further decrease in fugacity of tellurium (coupled with decreasing fugacity of sulfur) resulted in deposition of Au–Ag–Te and other tellurides.

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LETTERS
  • Tomoya TAMURA, Ryo SUGAYA, Atsushi KYONO
    2018 Volume 113 Issue 6 Pages 310-315
    Published: 2018
    Released: December 29, 2018
    [Advance publication] Released: December 19, 2018
    JOURNALS FREE ACCESS

    Low–temperature hydrothermal experiments were conducted to investigate mineral formation on the magnetite surfaces. The synthesized magnetite single crystals grown up to approximately 100 µm in size had a truncated–octahedral shape enclosed by {111}, {100}, and {110} planes, but the {100} plane was composed of many micro/nano pyramid arrays. The as grown magnetite was hydrothermally treated in deoxidized water at 100 °C for 30 days. The molecular hydrogen generation was detected by methylene blue colorimetric measurement. SEM observations showed that after the hydrothermal reaction the magnetite (100) surfaces were selectively dissolved and enormous number of hematite (α–Fe2O3) nanoparticles were epitaxially grown on the magnetite (111) surfaces. At the shallow depth of the magnetite (100) surfaces within 200 nm, magnetite was transformed to maghemite (γ–Fe2O3). This is the first report that maghemite is formed as a Fe(III)–oxide by the low–temperature hydrothermal alteration of magnetite. Both the selective dissolution and maghemite formation on the magnetite (100) surfaces would be responsible for the anisotropic diffusion property of Fe2+ cations in magnetite.

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  • Keiko MORI, Tatsuki TSUJIMORI, Nelson BONIFACE
    2018 Volume 113 Issue 6 Pages 316-321
    Published: 2018
    Released: December 29, 2018
    [Advance publication] Released: December 19, 2018
    JOURNALS FREE ACCESS

    We report a newly discovered assemblage of talc–kyanite in an amphibolite from the Isimani Suite of the Paleoproterozoic Usagaran Belt, central Tanzania. The amphibolite is characterized by the mineral assemblage of clinoamphibole, kyanite, talc with minor rutile, quartz, dolomite, and rare barite. The high Fe3+/(Fe3+ + Fe2+) ratio (0.48–0.80) of clinoamphibole and the presence of sulfate (barite) indicate a very–high oxidation state during metamorphism. P–T pseudosection modelling predicts that the studied talc– and kyanite–bearing amphibolites formed at high–pressure conditions (P > 1.0 GPa). Moreover, the modelling suggests formation of talc + kyanite + clinoamphibole at a highly oxidizing condition with CO2 fluid. This talc–kyanite association provides an index of high–pressure metamorphism of the Usagaran Belt and marks the oldest record of the talc–kyanite association in regional metamorphism in the Earth’s history.

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