A re-assessment of phase equilibria involving two liquids in the system K2O-Al2O3-FeO-SiO2

In previously published papers the presentation of experimental results involving two liquids has not adequately addressed the quaternary aspects of the phase equilibria. A theoretical examination of the types of quaternary and pseudo-ternary phase diagrams to be expected is prestend here. When applied to much of the previous data, such quaternary diagrams cope with the variation in the K₂O∶Al₂O₃ ratio of coexisting liquids, and all the previous data are shown to be in agreement with the existence of the assemblage tridymite-fayalite-two liquids for a limited temperature range along the field boundary between primary tridymite and primary fayalite. The absolute values of temperature in the different investigations are not easily reconciled without appealing to differences in experimental techniques, to differences in oxygen pressure, or to differences in K₂O loss during the experiments, as possible explanations of temperature differences greater than reasonable interlaboratory variations.