Electrochemical measurement of the free energy of almandine (Fe3Al2Si3O12) garnet

Alan B. Woodland*, Bernard J. Wood

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    14 Citations (Scopus)


    The free energy of the reaction (GISQ): 2 Fe + 2 3 Al2SiO5 + 4 3 SiO2 + O2 = 2 3 Fe3Al2Si3O12 metal sillimanite quartz almandine has been measured electrochemically between 1073 and 1173 K at 1 atmosphere pressure. Relative to quartz-fayalite-iron (QFI) equilibrium we obtain: log f{hook}O2GISQ - log f{hook}O2QFI (± 0.1) = -2.23 + 2400 T (1073-1173 K). In the experimental temperature range this result is in excellent agreement with data obtained from studies of garnet-rutile-sillimanite-ilmenite-quartz (GRAIL) equilibrium and for Fe-Mg partitioning between garnet and olivine. It is also in good agreement with recently published estimates based on other phase equilibrium data (Berman, 1988; Anovitz and Essene, 1987). The measured f{hook}O2 for GISQ equilibrium was found to increase with increasing cell edge of the synthetic almandine. The above value is for almandine with ao = 11.527 (±0.001) A ̊. Almandine with a cell edge of 11.534 Å gave f{hook}o2 values about 0.3 log units more oxidized. This increase in f{hook}O2 correlates with increasing Fe+3 of the synthetic garnet. 57Fe Mössbauer spectroscopy indicates that between 3 and 6 percent of the iron is Fe+3 in the high cell-edge material, whereas almandine with ao = 11.527 A ̊ is essentially ferric-free.

    Original languageEnglish
    Pages (from-to)2277-2282
    Number of pages6
    JournalGeochimica et Cosmochimica Acta
    Issue number9
    Publication statusPublished - 1989


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