A laboratory reconnaissance of the liquidus surface in the pyroxene system En-Di-Hd-Fs (MgSiO₃-CaMgSi₂O₆-CaFeSi₂O₆-FeSiO₃)

Thirty-four relatively homogeneous synthetic glasses, melted in metallic iron crucibles in nitrogen at 1 atm., were made to fall as close as possible to the pyroxene quadrilateral plane in the system MgO-CaO-FeO-SiO₂. As exact control by synthesis of the total FeO content is impossible, the glasses were analyzed, corrected by minor additions, re-fused, and reanalyzed. Phase equilibrium quenching runs were made on these glasses, in pure iron foil envelopes, to determine the general shape of the liquidus surface. Although the data are fragmentary, the major phase boundaries can be drawn with moderate accuracy. A quaternary liquidus field of olivine solid solutions extends into the system to a maximum Fs content of ~35 mole per cent and a minimum En content of ~41 mole per cent. The steep liquidus for silica (also quaternary equilibrium) includes all of the diagram above ~53-59 mole per cent Fs. The ternary undifferentiated liquidus for pyroxenes (and presumably wollastonite) is a shallow trough with lowest temperatures near hedanbergite; the solidus is rather close beneath.