Common Redox Buffers and Mineralogy
Common redox buffers
Redox buffers were developed in part to control oxygen fugacities in laboratory experiments to investigate mineral stabilities and rock histories. Each of the curves plotted in the fugacity-temperature diagram is for an oxidation reaction occurring in a buffer. These redox buffers are listed here in order of decreasing oxygen fugacity at a given temperature—in other words, from more oxidizing to more reducing conditions in the plotted temperature range. As long as all the pure minerals (or compounds) are present in a buffer assemblage, the oxidizing conditions are fixed on the curve for that buffer. Pressure has only a minor influence on these buffer curves for conditions in the Earth's crust.
MH magnetite-hematite
4 Fe3O4 + O2 = 6 Fe2O3
NiNiO nickel-nickel oxide
2 Ni + O2 = 2 NiO
FMQ fayalite-magnetite-quartz
3 Fe2SiO4 +O2 = 2 Fe3O4 + 3 SiO2
WM wustite-magnetite
3 Fe1-xO + O2 ~ Fe3O4
IW iron-wustite
2(1-x) Fe + O2 = 2 Fe1-xO
QIF quartz-iron-fayalite
2 Fe + SiO2 + O2 = Fe2SiO4
Read more about this topic: Mineral Redox Buffer
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