Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy;Vol.XVIII, Nos.1-2


Acmite-Vanadium Acmite Solid Solution in the Presence of H2O at High Pressures

Hariya, Yu;Yoshikawa, Kazuo

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Vanadium acmite (NaV3+Si2O6) was synthesized in presence of H2O at high pressure. The refractive indices of synthetic vanadium acmite are a=1.736 (3), γ=1.785 (5) and the cell parameters are a=9.640 (1) Å, b=8.748 (2) Å, c=5.297 (1) Å, β=106.89 (1)° and V=427.4 (1) Å3 . This pyroxene is stable at least up to 30 kb at 800℃ with H2O under reducing environment, and it melts incongruently to occur opaque crystal and liquid. Acmite75 -vanadium acmite25, acmite50-vanadium acmite50 and acmite25-vanadium acmite75 compositions also crystallizes easily at 500 bars and 600℃ with H2O. The cell parameters of synthetic acmite-vanadium acmite series change linearlly with molar compositions. This systematic changes in cell parameters suggest that a continuous solid solution series exists between NaFe3+Si2O6 and NaV3+Si2O6, Melting of pyroxene of composition acmite50 -vanadium acmite50 is relatively insensitive to PH2O in the studied pressure range of 5 - 30 kb.