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 FeO + O ⇌ 6 FeO
NiNiO: nickel-nickel oxide:
: 2 Ni + O ⇌ 2 NiO
FMQ: fayalite-magnetite-quartz:
: 3 FeSiO + O ⇌ 2 FeO + 3 SiO
WM: wustite-magnetite:
: 3 FeO + O ~ FeO
IW: iron-wustite:
: 2 (1-x) Fe + O ⇌ 2 FeO
QIF: quartz-iron-fayalite:
: 2 Fe + SiO + O ⇌ FeSiO