Both Fused Silica and Fused Quartz are extremely pure materials featuring very low thermal expansion and excellent optical qualities. They both work well in areas that require good chemical resistance. Unlike fused quartz, which originates from mined, natural quartz or silica sand, fused silica is produced synthetically by the vapor phase hydrolysis of a silicon halide. The resulting product is vitreous, non-crystalline, of the highest purity and one of the most transparent glasses made. Its transmission and homogeneity exceed those of crystalline quartz without the problems of orientation and temperature instability inherent in the crystalline form. Fused silica, with a softening temperature of around 1,600 degrees Celsius, a very low coefficient of thermal expansion and resistance to thermal shock and effects of radiation, is the material of choice for various applications.