The thermal expansion coefficient of quartz glass is only 1 / 10-1 / 20 of that of ordinary glass. The purity of quartz glass has an effect on the coefficient of thermal expansion. The linear expansion coefficient (0-1000oc) of transparent quartz glass is 5.4 × 10-7, that of opaque quartz glass is 5.5 × 10-7, and that of high-purity synthetic quartz glass is 4.9 × 10-7 (0-200oc) - 5.0 × 10-7 (5-35oc).