The Mg2GeO4 olivine-spinel phase transition

Nancy L. Ross, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

46 Scopus citations

Abstract

Enthalpies and entropies of transition for the Mg2GeO4 olivine-spinel transformation have been determined from self-consistency analyses of Dachille and Roy's (1960), Hensen's (1977) and Shiota et al.'s (1981) phase boundary studies. When all three data sets are analyzed simultaneously, ΔH973 and ΔS973 are constrained between -14000 to -15300 J mol-1 and -13.0 to -14.1·J mol-1 K-1, respectively. High-temperature solution calorimetric experiments completed on both polymorpha yield a value of -14046±1366 J mol-1 for ΔH973. Kieffer-type lattice vibrational models of Mg2GeO4 olivine and spinel based on newly-measured infrared and Raman spectra predict a value of -13.3±0.6 J mol-1 K-1 for ΔS1000. The excellent agreement between these three independent determinations of ΔH and ΔS suggests that the synthesis runs of Shiota et al. (1981) at high pressures and temperatures bracket equilibrium conditions. In addition, no configurational disorder of Mg and Ge was needed to obtain the consistent parameters quoted. The Raman spectrum and X-ray diffractogram show that little disorder, if any, is present in Mg2GeO4 spinel synthesized at 0.2 GPa and 973-1048 K.

Original languageEnglish (US)
Pages (from-to)473-481
Number of pages9
JournalPhysics and Chemistry of Minerals
Volume14
Issue number5
DOIs
StatePublished - Sep 1987
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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