Ferric iron in orthopyroxene: a Mössbauer spectroscopic study |
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| Authors: | Hans Annersten Martin Olesch Friedrich A Seifert |
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| Institution: | Mineralogisches Institut der Universität Kiel, D-2300, Kiel, Germany |
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| Abstract: | Ferric iron solid solution in synthetic orthopyroxene has been studied along the joins MgSiO3-Al2O3 · Fe2O3 and MgSiO3-Fe2O3. The partially reduced synthetic orthopyroxenes showed that major incorporation of ferric iron can only occur together with a concomitant incorporation of Al. Maximum solid solution of ferric iron along the join MgSiO3-Fe2O3 was found to be only 0.63 wt% Fe2O3 at 1000°C and 2 kb total pressure. From the observed Mössbauer parameters octahedral ferric iron can be assigned to the MI position in orthopyroxene. Incorporation of Fe3+ and/or Al will increase the disorder of Fe2+ and Mg between the M1 and M2 sites, which is also observed in a ferric iron-containing aluminous orthopyroxene of metamorphic origin. In the assemblage orthopyroxene + sillimanite + quartz the ferric iron content of orthopyroxene is directly related to oxygen fugacity. |
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