Thermodynamic Aspects of Phase Boundary Among α-, β-, and γ-Mg2SiO4

  1. Murli H. Manghnani and
  2. Yasuhiko Syono
  1. Toshifumi Ashida1,
  2. Shoichi Kume1 and
  3. Eiji Ito2

Published Online: 21 MAR 2013

DOI: 10.1029/GM039p0269

High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto

High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto

How to Cite

Ashida, T., Kume, S. and Ito, E. (1987) Thermodynamic Aspects of Phase Boundary Among α-, β-, and γ-Mg2SiO4 , in High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto (eds M. H. Manghnani and Y. Syono), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM039p0269

Author Information

  1. 1

    College of General Education, Osaka University, Toyonaka, Osaka, Japan

  2. 2

    Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori, Japan

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1987

ISBN Information

Print ISBN: 9780875900667

Online ISBN: 9781118664124

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Keywords:

  • Mineralogy and Crystal Chemistry;
  • Phase transformations;
  • High Pressure-High Temperature Research

Summary

Molar heat capacities of three polymorphs (α, β, γ) of Mg2SiO4 were measured in the temperature range of 180–700 K by means of differential scanning calorimetry (DSC). The results were extrapolated towards low and high temperatures, and the entropy of each phase was evaluated in the range of 0–2000 K. The phase boundaries for α-β and for α-γ were determined by thermodynamic calculations using these entropies and additional reported data on enthalpies of formations, compressibilities, and thermal expansions. The boundaries of α-β ana α-γ above 1000 K were roughly approximated by the following linear relations

$$\eqalign{ & P = 11.68 + 0.0025\,T,\,{\rm for}\,{\rm \alpha } - \beta \cr & P = 11.08 + 0.0048\,T,\,{\rm for}\,\beta - \gamma \cr}$$

where P is in GPa and T is in degrees K.

The triple point, where the three phases coexist, was found to be located at 13±0.5 GPa and 400–600 K. The results for the boundaries were compared with those obtained by two synthesis experiments and found to be in agreement with the results reported by Suito (1977) for above 1000 K.