Fusion of Quartz and Cristobalite

The melting point of quartz is established to be below 1450°C. and possibly above 1400°C. The product of fusion is a liquid of high viscosity which undergoes slow transformation to give the commonly encountered vitreous silica. At temperatures between 1450deg; and 1700°C., both cristobalite and glass are formed when quartz is heated in air for periods in excess of 15 minutes. The quartz‐cristobalite transformation is sensitive to the ambient atmosphere. After heating to temperatures above 1730°C., inhomogeneities are still present in both fused quartz and fused cristobalite in the form of unmelted microcrystals. Their presence is indicated by X‐ray diffraction, metallographic, infrared, and hardness measurements.