Summary: The system sanbornite-celsian has been investigated by the quenching method, and the results compared with earlier studies. The system is essentially a simple binary eutectic system with little or no solid solution. The eutectic is located at a composition of 69% sanbornite and 31% celsian (by weight) and at a temperature of 1227±3°C. No evidence for substantial solid solution of celsian in sanbornite, as reported in previous work, was found. Paracelsian, a naturally occurring polymorph of celsian, was not encountered in the study.