What is the difference between borosilicate glass and quartz?

There are many differences between borosilicate glass and quartz, either pure- or synthetic-fused silica types. The main differences are the percentage of compounds and the percentage of silica or SiO2 in the glass. Borosilicate is usually in the 80% range, while quartz is over 99%. Quartz is also capable of handling much higher temperatures up to 1,100° C. Quartz is typically used for high temperature applications, or where optical quality or dielectric properties are critical. Impurities in borosilicate glass are measured in percent; impurities in quartz are measured in PPM.