Quartz is one of the most common minerals in the Earth’s crust. As a mineral name, quartz refers to a specific chemical compound (silicon dioxide, or silica, SiO2), having a specific crystalline form (hexagonal). It is found is all forms of rock: igneous, metamorphic and sedimentary. Quartz is physically and chemically resistant to weathering. When quartz-bearing rocks become weathered and eroded, the grains of resistant quartz are concentrated in the soil, in rivers, and on beaches. The white sands typically found in river beds and on beaches are usually composed mainly of quartz, with some white or pink feldspar as well.
Quartz has great economic importance. Large amounts of quartz sand (also known as silica sand) are used in the manufacture of glass and ceramics and for foundry moulds in metal casting. Crushed quartz is used as an abrasive in sandpaper, silica sand is employed in sandblasting, and sandstone is still used whole to make whetstones, millstones, and grindstones. Silica glass (also called fused quartz) is used in optics to transmit ultraviolet light. Tubing and various vessels of fused quartz have important laboratory applications, and quartz fibres are employed in extremely sensitive weighing devices.
Quartz crystal is one of several minerals which are piezoelectric, meaning that when pressure is applied to quartz, a positive electrical charge is created at one end of the crystal and a negative electrical charge is created at the other. These properties make quartz valuable in electronics applications. Electronics-grade manufactured quartz is used in a large number of circuits for consumer electronics products such as computers, cell phones, televisions, radios, electronic games, etc. It is also used to make frequency control devices and electronic filters that remove defined electromagnetic frequencies.