Quartz is a hard, glossy mineral made of silicon and oxygen. It is found in most kinds of rocks in colourless, often transparent form. There are also coloured varieties including semi-precious stones such as amethyst and citrine. Pure quartz is called rock crystal also. In appearance it looks like glass. It has six sided crystalline structure. It ranks 7 on the Mohs’ scale of hardness and is resistant to chemical or mechanical breakdown.
Quartz is extremely hard and will scratch glass. It melts at a very high temperature. It can be made into tubes, sheets or blocks. It can also be blown into various shapes by using oxy-hydrogen flame.
Quartz has great economic importance. Sandstone, composed mainly of quartz, is an important building stone. Large amount of quartz sand is used in the manufacture of glass and porcelain and in metal casting for foundry moulds. Quartz is used as an abrasive in sandpaper and grindstones. It is used to make prisms and lenses which can transmit ultra-violet light. Tubing and various vessels of fused quartz have important laboratory application. It is also used in ornamental work and industry where its reaction to electricity makes it valuable in electronic instruments. Quartz fibres are used in extremely sensitive weighing devices.
Quartz is a piezoelectric material, i.e. when pressure is applied across the two surfaces of a quartz crystal, an electric voltage develops across the crystal and when voltage is applied across the two faces of the crystal, and it expands, or contracts. Due to this property, it can help to change electric signals into sound waves and vice versa. The piezoelectric property of quartz plays an important role in radios, television and radar. Quartz oscillators are used in Quartz crystal watches to give accurate time.
Natural quartz crystals of commercial grade are obtained from Brazil. Quartz can also be made synthetically.