Additions of Al2O3, Na2O or K2O all lower the immiscibility temperature for liquid-liquid phase separation in the CaO-SiO2 system as the region of immiscibility is extended into the ternary field. Simultaneous additions of K2O and Al2O3 or Na2O and Al2O3 are found to further extend the compositional region of immiscibility which reaches a maximum with equimolar additions of alkali and alumina. These results are attributed to the ability of KAlO2 or NaAlO2 units to substitute for SiO2 in the liquid structure. As a consequence of liquid-liquid immiscibility, wollanstonite crystallizes from the calcia-rich liquid phase. STEM analysis has been applied to the phase-separated glasses to determine the approximate K2O-Al2O3 ratio and overall composition of each phase to locate tie-lines for the liquid-liquid immiscibility. The tie lines are roughly parallel to the CaO-SiO2 join.