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

• 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

• OHFUJI Hiroaki

  Geodynamics Research Center, Ehime 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 ⁵⁷Fe 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 ⁵⁷Fe Mössbauer spectrum of the olivine separate consisted of three doublets assigned to Fe²⁺ at the M1, Fe²⁺ at the M2 and Fe³⁺ at the octahedral sites. The Fe²⁺:Fe³⁺-ratio is 95(3):5(1). By applying this value to the average Fe content, Fe²⁺ and Fe³⁺ are calculated to be 0.34(1) and 0.018(4) apfu, respectively. Since the Fe³⁺ within olivine detected in this study is not due to any Fe³⁺-bearing impurity, Fe³⁺ could be located at the octahedral site within the olivine structure. The quadrupole splitting value of the Fe³⁺-Mössbauer doublet [0.53(5) mm/s] in Kasayama olivine is significantly lower than published data for Fe³⁺ at the M2 site in olivine, and in laihunite. This suggests possible distribution of Fe³⁺ at the M1 site. Fe³⁺ 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

  Japan Association of Mineralogical Sciences

Keywords

• Olivine
• Fe oxidation state
• High temperature oxidation
• Kasayama volcano
• Scoria

Details

• CRID: 1390282681523280896
• NII Article ID: 10031134516
• NII Book ID: AA11460926
• DOI: 10.2465/jmps.120605
• COI: 1:CAS:528:DC%2BC3sXjtlKjsLw%3D
• ISSN: 13493825
• ISSN: 13456296
• Text Lang: en
• Data Source:
  • JaLC
  • Crossref
  • CiNii Articles
  • KAKEN
• Abstract License Flag: Disallowed