Oxidation state of Fe in olivine in andesitic scoria from Kasayama volcano, Hagi, Yamaguchi Prefecture, Japan

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Author(s)

    • EJIMA Terumi
    • Department of Materials Creation and Circulation Technology, Graduate School of Science and Engineering, Shimane University
    • AKASAKA Masahide
    • Department of Materials Creation and Circulation Technology, Graduate School of Science and Engineering, Shimane University
    • NAGAO Takashi
    • Department of Earth Sciences, Graduate School of Science and Engineering, Yamaguchi University

Abstract

The oxidation state of an olivine phenocryst separate from clinopyroxene-olivine andesitic black scoria with red-brown tint from Kasayama volcano, Hagi, Yamaguchi Prefecture, was determined using <sup>57</sup>Fe Mössbauer spectroscopy, to examine the effect of high temperature oxidation on the oxidation state of Fe.<br>  The olivine phenocrysts examined were euhedral to subhedral in form, typically fractured, and about 0.2-1 mm in maximum dimension. Small amounts of Fe-bearing precipitate minerals often occur on the rims of olivine phenocrysts in the black scoria with red-brown tint, and near subhedral Cr-rich magnetite with about 5 μm in diameter. Olivine phenocrysts lacking such precipitates and inclusions were separated from a sample using an isodynamic separator and handpicking under a binocular microscope. Examination by optical microscopy, electron microprobe analysis, Raman spectroscopy, and high-resolution transmission microscopy proved no precipitates in the separated olivine phenocrysts. Average Fo value and Fe content of the olivines were 81 mol% and 0.36 atoms per formula unit (apfu), respectively. The <sup>57</sup>Fe Mössbauer spectrum of the olivine separate consisted of three doublets assigned to Fe<sup>2+</sup> at the M1, Fe<sup>2+</sup> at the M2 and Fe<sup>3+</sup> at the octahedral sites. The Fe<sup>2+</sup>:Fe<sup>3+</sup>-ratio is 95(3):5(1). By applying this value to the average Fe content, Fe<sup>2+</sup> and Fe<sup>3+</sup> are calculated to be 0.34(1) and 0.018(4) apfu, respectively. Since the Fe<sup>3+</sup> within olivine detected in this study is not due to any Fe<sup>3+</sup>-bearing impurity, Fe<sup>3+</sup> could be located at the octahedral site within the olivine structure. The quadrupole splitting value of the Fe<sup>3+</sup>-Mössbauer doublet [0.53(5) mm/s] in Kasayama olivine is significantly lower than published data for Fe<sup>3+</sup> at the M2 site in olivine, and in laihunite. This suggests possible distribution of Fe<sup>3+</sup> at the M1 site. Fe<sup>3+</sup> within olivine in the black scoria with red-brown tint is considered to have been generated at high temperatures (perhaps above 800 °C).

Journal

  • Journal of Mineralogical and Petrological Sciences

    Journal of Mineralogical and Petrological Sciences 107(6), 215-225, 2012-12-01

    Japan Association of Mineralogical Sciences

References:  44

Cited by:  1

Codes

  • NII Article ID (NAID)
    10031134516
  • NII NACSIS-CAT ID (NCID)
    AA11460926
  • Text Lang
    ENG
  • Article Type
    Journal Article
  • ISSN
    13456296
  • Data Source
    CJP  CJPref  J-STAGE 
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