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.
Quartz appears in a number of colored varieties, like amethyst (violet), citrine (yellow), or smoky quartz (gray, brown to black), It also occurs in dense forms with no visible crystals like the multi-colored agate and the gray flint.
Quartz is an important rock-forming mineral being a constituent of many common rocks like granite.
Colored quartz varieties have been used for jewelry for ages, but most quartz is used as a component of concrete: quartz sand and quartz gravel.
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.
A well-known application of quartz is its use as an oscillator in electric circuits in watches and computers. Less well known is, for example, its use as a membrane in ultrasonic devices.
Quartz is of course the major “ore” of silicon used in the integrated circuits “chips” of your computer.