SiO2 (Quartz Crystal)
Optically, Crystalline Quartz is used extensively as a wave retardation medium. The birefringent properties of Quartz are of use in quarter-wave plates and in polarisers. Quartz should not be processed or used at temperatures greater than 490 °C. Crystalline quartz is also used for electronic filters and resonators. However, Crystran Ltd. does not deal in material for this application.