The equilibrium primary phases that precipitate from cryolite‐alumina melts are cryolite, to the left of the eutectic, and corundum, to the right of the eutectic. No solid solubility of alumina in the cryolite phase was found. Evidence is presented in the form of photomicrographs and x‐ray powder patterns that a new alumina phase is obtained by extremely rapid quenching of the liquid. The x‐ray pattern of this phase is similar to the aluminum silicate, mullite. It is thought to result from the disproportionation of an oxyfluoride complex in the melt and is perhaps a skeletal arrangement with some of the characteristics of the oxyfluoride precursor. This new alumina phase is metastable and transforms through eta‐alumina to corundum on heating.