Studies in the System BaO‐Al ₂ O ₃ −SiO ₂ : V. The Ternary System Sanbornite‐Celsian‐Silica *

Phase relations in the BaSi 2 O 5 −BaAl 2 Si 2 O 8 −SiO 2 portion of the system BaO‐Al 2 O 3 −SiO 2 were reinvestigated by the standard quenching method. In contrast to the results of earlier studies, this portion is revealed as a simple ternary system; its features include a ternary eutectic at 1122°±7°C and a composition of BaO 35.2, Al 2 O 3 9.5, and SiO 2 55.3 wt%, involving the phases sanbornite, celsian, and silica. These results are compared with those of earlier quenching studies, with relations in analogous ternary systems, with data from hydrothermal experiments, and with observations of natural mineral assemblages.