Calorimetric study of high-pressure polymorphs of MnSiO3

Masaki Akaogi, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

With increasing pressure, MnSiO3 rhodonite stable at atmospheric pressure transforms to pyroxmangite, then to clinopyroxene and further to tetragonal garnet, which finally decomposes into MnO (rocksalt) plus SiO2 (stishovite). High temperature solution calorimetry of synthetic rhodonite, clinopyroxene and garnet forms of MnSiO3 was used to measure the enthalpies of these transitions. ΔH9740for the rhodonite-clinopyroxene and ΔH2980for the clinopyroxene-garnet transition are 520±490 and 8,270±590 cal/mol, respectively. The published data on the enthalpy of the rhodonite-pyroxmangite transition, phase equilibrium boundaries, compressibility and thermal expansion data are used to calculate entropy changes for the transitions. The enthalpy, entropy and volume changes are very small for all the transitions among rhodonite, pyroxmangite and clinopyroxene. The calculated boundary for the clinopyroxene-garnet transition is consistent with the published experimental results. The pyroxene-garnet transition in several materials, including MnSiO3, is characterized by a relatively small negative entropy change and large volume decrease, resulting in a small positive P - T slope. The disproportionation of MnSiO3 garnet to MnO plus stishovite and of Mn2SiO4 olivine to garnet plus MnO are calculated to occur at about 17-18 and 14-15 GPa, respectively, at 1,000-1,500 K.

Original languageEnglish (US)
Pages (from-to)317-323
Number of pages7
JournalPhysics and Chemistry of Minerals
Volume12
Issue number6
DOIs
StatePublished - Nov 1985

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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