Orthopyroxene magnesian

Reactions 4 and 5. Bohlen and Boettcher (1981) studied the effect of the presence of magnesian and manganoan terms in the mixture on the distribution of ferrous component between orthopyroxene and olivine according to the reaction... 

Reactions 12 and 13. The coexistence of plagioclase, orthopyroxene, garnet, and quartz may be expressed as an equilibrium involving ferrous and/or magnesian components, as seen in the preceding case ... 

Fig. 93. Equilibrium of magnesian-iron minerals in rocks with excess silica. A. In silicate iron-formations (aqueous fluid. Cum + Px -t- OH- Q association). B. In carbonate iron-rich rocks (carbonic acid fluid. Car -(- Px -I- 01 -t- Q association). Figures indicate maximum iron content of orthopyroxene in association with quartz and olivine.

Fig. 3. Three possible mechanisms that could allow the segregation and accumulation near the surface of the Earth of highly magnesian olivine and orthopyroxene.

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