Quartz

Quartz is a very common mineral, a chemical compound of silicon and oxygen, silicon dioxide SiO2, commonly called silica. If pure, quartz is a colorless, transparent, and very hard crystalline material of glass-like look. The well-known rock crystals - six-sided prisms with a six-sided pyramid at their ends - are simply well formed crystals of quartz.

Pure Quartz is needed for producing glass, ceramics, and chemical apparatus. Quartz glass, also known as "fused quartz" or "fused silica" (produced by quickly cooling molten quartz) has a number of interesting properties: its thermal expansion coefficient is very low, it is transparent for ultraviolet light, it is chemically almost inert, and it can form very thin but strong threads used in physical instruments.