Contributions to Mineralogy and Petrology

, Volume 82, Issue 1, pp 75–90

The system Fe-Si-O: Oxygen buffer calibrations to 1,500K

  • J. Myers
  • H. P. Eugster

DOI: 10.1007/BF00371177

Cite this article as:
Myers, J. & Eugster, H.P. Contr. Mineral. and Petrol. (1983) 82: 75. doi:10.1007/BF00371177


The five solid-phase oxygen buffers of the system Fe-Si-O, iron-wuestite (IW), wuestite-magnetite (WM), magnetite-hematite (MH), quartz-iron-fayalite (QIF) and fayalite-magnetite-quartz (FMQ) have been recalibrated at 1 atm pressure and temperatures from 800°–1,300° C, using a thermogravimetric gas mixing furnace. The oxygen fugacity, \(f_{{\text{O}}_{\text{2}} }\) was measured with a CaO-doped ZrO2 electrode. Measurements were made also for wuestite solid solutions in order to determine the redox behavior of wuestites with O/Fe ratios varying from 1.05 to 1.17. For FMQ, additional determinations were carried out at 1 kb over a temperature range of 600° to 800° C, using a modified Shaw membrane. Results agree reasonably well with published data and extrapolations.

The reaction parameters K, ΔGro, ΔHro, and ΔSrowere calculated from the following log \(f_{{\text{O}}_{\text{2}} }\)/T relations (T in K):

$$\begin{gathered} {\text{IW }}\log f_{{\text{O}}_{\text{2}} } = - 26,834.7/T + 6.471\left( { \pm 0.058} \right) \hfill \\ {\text{ }}\left( {{\text{800}} - 1,260{\text{ C}}} \right), \hfill \\ {\text{WM }}\log f_{{\text{O}}_{\text{2}} } = - 36,951.3/T + 16.092\left( { \pm 0.045} \right) \hfill \\ {\text{ }}\left( {{\text{1,000}} - 1,300{\text{ C}}} \right), \hfill \\ {\text{MH }}\log f_{{\text{O}}_{\text{2}} } = - 23,847.6/T + 13.480\left( { \pm 0.055} \right) \hfill \\ {\text{ }}\left( {{\text{1,040}} - 1,270{\text{ C}}} \right), \hfill \\ {\text{QIF }}\log f_{{\text{O}}_{\text{2}} } = - 27,517.5/T + 6.396\left( { \pm 0.049} \right) \hfill \\ {\text{ }}\left( {{\text{960}} - 1,140{\text{ C}}} \right), \hfill \\ {\text{FMQ }}\log f_{{\text{O}}_{\text{2}} } = - 24,441.9/T + 8.290\left( { \pm 0.167} \right) \hfill \\ {\text{ }}\left( {{\text{600}} - 1,140{\text{ C}}} \right). \hfill \\ \end{gathered}$$

These experimentally determined reaction parameters were combined with published 298 K data to determine the parameters Gf, Hf, and Sf for the phases wuestite, magnetite, hematite, and fayalite from 298 K to the temperatures of the experiments. The T−\(f_{{\text{O}}_{\text{2}} }\) data for wuestite solid solutions were used to obtain activities, excess free energies and Margules mixing parameters.

The new data provide a more reliable, consistent and complete reference set for the interpretation of redox reactions at elevated temperatures in experiments and field settings encompassing the crust, mantle and core as well as extraterrestrial environments.

Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • J. Myers
    • 1
  • H. P. Eugster
    • 2
  1. 1.Department of GeologyUniversity of Wyoming LaramieWyomingUSA
  2. 2.Department of Earth and Planetary SciencesThe Johns Hopkins UniversityBaltimoreUSA
  3. 3.Rockwell Hanford OperationsRichlandUSA