· The glass fiber process. Textilegrade glass fibers are made from silica (SiO 2) sand, which melts at 1720°C/3128° 2 is also the basic element in quartz, a naturally occurring rock. Quartz, however, is crystalline (rigid, highly ordered atomic structure) and is 99% or more SiO SiO 2 is heated above 1200°C/2192°F then cooled ambiently, it crystallizes and becomes quartz.