Study of the MgGeO3 polymorphs (orthopyroxene, clinopyroxene, and ilmenite structures) by calorimetry, spectroscopy, and phase equilibria

N. L. Ross, A. Navrotsky

Research output: Contribution to journalArticlepeer-review

61 Scopus citations

Abstract

Below 6 GPa, MgGeO3 transforms with increasing pressure from an orthopyroxene, to a clinopyroxene, and finally to an ilmenite structure. Thermodynamic parameters for MgGeO3 (opx → cpx) and MgGeO3 (cpx → ilm) have been constrained by high-temperature solution calorimetric experiments, lattice vibrational calculations, and phase-equilibrium studies. The enthalpy and entropy of MgGeO3 (opx → cpx) determined in this study are -3440 ± 681 J.mol- 1 and -1.5 to -3.0 J.mol-1.K-1, respectively, which are comparable to magnitude to values for other phase transitions among pyroxenes and pyroxenoids. The values of ΔH0 973 and ΔS0 973 for MgGeO3 (cpx → ilm) determined from calorimetry and lattice vibrational calculations are 7808 ± 561 J.mol-1 and -7.5 ± 1.5 J.mol-1.K-1, respectively. These values are consistent with new experimental reversals of the MgGeO3 (cpx → ilm) phase boundary, P (in GPa) = 1.913 + 0.0018T (in K). -Authors

Original languageEnglish (US)
Pages (from-to)1355-1365
Number of pages11
JournalAmerican Mineralogist
Volume73
Issue number11-12
StatePublished - 1988
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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