Eight compositions were synthesized along the join. Orthopyroxene crystallized at X = Mn/(Mn + Mg) = 0.0-0.3, clinopyroxene at X = 0.4-0.5, and pyroxmangite at X = 0.65-1.0, consistent with the composition ranges that have been inferred by examination of metamorphic rock assemblages. Unit cell dimensions for these phases and for rhodonite (X = 1.0) are presented. Microprobe chemical analyses reveal that compositional homogeneity was not always achieved, even in runs at 850°C and 1 kbar water pressure lasting 1000-2000 hours. For the bulk composition range X = 0.0-0.3, below 725°C, clinoam-phibole and/or talc occurred instead of orthopyroxene. Diagrams are used to suggest possible phase relations among the metasilicates, cummingtonite or anthophyllite, olivine, and talc.

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