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Physics and Chemistry of Minerals

, Volume 14, Issue 5, pp 473–481 | Cite as

The Mg2GeO4 olivine-spinel phase transition

  • Nancy L. Ross
  • Alexandra Navrotsky
Article

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 andΔS973 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 forΔH973. 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 forΔS1000. The excellent agreement between these three independent determinations ofΔH andΔS 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.

Keywords

Entropy Enthalpy Phase Transition Olivine Raman Spectrum 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • Nancy L. Ross
    • 1
  • Alexandra Navrotsky
    • 2
  1. 1.Geophysical LaboratoryCarnegie Institute of WashingtonWashington, D.C.USA
  2. 2.Department of Geological and Geophysical Sciences, Guyot HallPrinceton UniversityPrincetonUSA

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