purest form of quartz

Quartz glass is the purest form of SiO2 and therefore the most valuable and sophisticated variety. Extremely clear glass can be used for optical fibers. Therefore synthetic quartz glass is used to transmit light across many kilometers. Lots of glasses are impermeable for ultraviolet radiation, but only pure fused silica (only SiO2) is permeable for wavelengths
< 350 nm (UV). Quartz glass also exists as an opaque variety and with different coloration to change the physical and chemical properties like transmission or absorption for specific wavelength (filter glass). The opaque material at Heraeus, OM 100, is also used as a heat barrier or for diffuse scattering of IR radiation.