Crystal chemistry and Raman spectroscopy of momoiite from Japan

• ENDO Shunsuke

  Department of Earth Science, Interdisciplinary Faculty of Science and Engineering, Shimane University

• NAGASHIMA Mariko

  Graduate School of Sciences and Technology for Innovation, Yamaguchi University

• ENAMI Masaki

  Institute for Space–Earth Environmental Research, Nagoya University

抄録

Momoiite, a Mn²⁺– and V³⁺–dominant member of the garnet group, has been reported from metamorphosed manganese deposits in Japan. Near end–member momoiite (Mn₃V₂Si₃O₁₂) has not yet been found in nature, and the chemical composition of natural momoiite is written as (Mn,Ca)₃(V,Al)₂Si₃O₁₂, which represents intermediate compositions in solid–solution series between spessartine and Mn–rich goldmanite. Single–crystal X–ray diffraction data were obtained for an optically isotropic momoiite crystal from the Fujii mine, Fukui Prefecture, Japan. Structural refinement in the Ia3d space group converged to R₁ = 1.45%, and the lattice constant is a = 11.8745(7) Å (Z = 8). The refined structural formula is ^X(Mn_1.763Ca_1.237)_Σ3.000^Y(V_1.461Al_0.539)_Σ2.000^ZSi₃O₁₂, which is consistent with electron microprobe analysis. Raman spectra of the solid–solution series between spessartine and Mn–rich goldmanite show continuous change in peak positions. The Si–O stretching and O–Si–O bending vibrations show downward frequency shifts with decreasing Mn/(Mn + Ca) and increasing V/(V + Al), which are associated with increase in mean ionic radii in the X and Y sites. The Al–V substitution controls the frequency shifts of the O–Si–O bending vibrations much more effectively than the Mn–Ca substitution. In contrast, the frequency shift of the SiO₄ rotation mode shows strong correlation with the Mn–Ca substitution and is apparently independent on the Al–V substitution. This behavior suggests that the rotation of the SiO₄ tetrahedron is strongly influenced by sharing two edges with XO₈–dodecahedra. Crystal–chemical and Raman spectroscopic data of natural momoiite are consistent with those expected as an intermediate composition in the solid–solution series.

収録刊行物

• Journal of Mineralogical and Petrological Sciences

  Journal of Mineralogical and Petrological Sciences 114 (4), 161-169, 2019

  一般社団法人　日本鉱物科学会

キーワード

• Crystal chemistry
• Garnet
• Momoiite
• Raman spectroscopy
• Solid–solution

詳細情報

• CRID: 1390845702292408448
• NII論文ID: 130007719449
• DOI: 10.2465/jmps.190219
• ISSN: 13493825
• ISSN: 13456296
• Web Site: https://www.jstage.jst.go.jp/article/jmps/114/4/114_190219/_pdf
• 本文言語コード: en
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