Summary: The high-temperature phase equilibrium relationships in the system diopside-anorthite—åkermanite have been investigated by the quenching method. This system may be regarded as essentially a simple eutectic system. The eutectic is located at the composition 9 diopside:44 anorthite:47 åkermanite (by weight) and at a temperature of 1226° C. Åkermanite is a stable phase at least as low as this temperature. Triclinic anorthite is the only form of CaAl₂Si₂O₈ encountered in the liquidus range of temperatures.