Abstract
The solubility of alumina in orthopyroxene coexisting with spinel and forsterite has been discussed using a simple mixing model of orthopyroxene and it was revealed that the recent experimental results in MgO–Al2O3–SiO2 system (MacGregor, 1974) do not agree with the model. Reexamination of the system gave the results which are in good agreement with thermodynamically calculated alumina solubility in orthopyroxene and indicated that, in the spinel-stability field, it is not sensitive to pressure.
