The partition of Si, A1, Ti, Fe 3+, Mg, Fe 2+, Mn, Ca and Na between coexisting Carich and Ca-poor pyroxenes from a wide variety of igneous and metamorphic rocks have been investigated systematically. Many of the distributions, and especially those for the partition of Ti, Mg, Fe 2+, Mn and Na, indicate characteristic trends for pyroxenes from the various petrologic groups identified.
The partition of Mg, Fe 2+ and Mn correlate with inferred cooling rates, the partition coefficients of pyroxenes from extruded and other quickly cooled rocks most nearly approaching unity. In contrast, the partition of Si and Ti and the absolute amounts of ALl may be related to the physicoehemical conditions prevailing during original crystallisation; Ti being particularly relatively enriched in Ca-rich pyroxenes of ultramafie associations.
The trends of the compositions of the Ca-rich pyroxenes plotted in the pyroxene quadrilateral also correlate with cooling rates and comparison with the limited data available on the phase relations of coexisting pyroxenes suggests that sub-solidus chemical readjustments have occurred in both phases.