Preferential dissolution of SiO2 from enstatite to H2 fluid under high pressure and temperature

Ayako Shinozaki, Hiroyuki Kagi, Hisako Hirai, Hiroaki Ohfuji, Taku Okada, Satoshi Nakano, Takehiko Yagi

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Stability and phase relations of coexisting enstatite and H2 fluid were investigated in the pressure and temperature regions of 3.1–13.9 GPa and 1500–2000 K using laser-heated diamond-anvil cells. XRD measurements showed decomposition of enstatite upon heating to form forsterite, periclase, and coesite/stishovite. In the recovered samples, SiO2 grains were found at the margin of the heating hot spot, suggesting that the SiO2 component dissolved in the H2 fluid during heating, then precipitated when its solubility decreased with decreasing temperature. Raman and infrared spectra of the coexisting fluid phase revealed that SiH4 and H2O molecules formed through the reaction between dissolved SiO2 and H2. In contrast, forsterite and periclase crystals were found within the hot spot, which were assumed to have replaced the initial orthoenstatite crystals without dissolution. Preferential dissolution of SiO2 components of enstatite in H2 fluid, as well as that observed in the forsterite H2 system and the quartz H2 system, implies that H2-rich fluid enhances Mg/Si fractionation between the fluid and solid phases of mantle minerals.

Original languageEnglish
Pages (from-to)277-285
Number of pages9
JournalPhysics and Chemistry of Minerals
Issue number4
Publication statusPublished - 2016 Apr 1


  • H fluid
  • Laser-heated diamond-anvil cell
  • Pyroxene
  • SEM
  • TEM


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