Quartz

Quartz (SiO₂), a common mineral, is the product of the two most prevalent elements in the earth's crust : silicon and oxygen . Quartz can be found as giant crystals or small grains, and is the main component of most types of sand . It is the hardest common mineral, and for this reason is often used in the making of sandpaper, grindstones, polishers, and industrial cleaners. Though quartz is clear and glassy in its large crystal form, called rock quartz, it also can be found in several shades of coloration, the most familiar being rose quartz (pink), smoky quartz (brown), and amethyst (purple).

Quartz has a variety of scientific and industrial uses, chiefly because it possesses piezoelectricity. Discovered by the French physicist and chemist Pierre Curie (1859–1906), the piezoelectric effect is a phenomenon demonstrated by certain crystals: when squeezed or stretched, a voltage is produced across the crystal's face. This effect is reversible as well, for when a voltage is applied to a piezoelectric crystal it will stretch; if the polarity of the voltage is alternated, the crystal will rapidly expand and contract, producing a vibration. It is this vibration that makes quartz especially useful. Every kind of piezoelectric crystal has a natural vibration frequency that is determined by its thickness—the thinner the crystal, the higher the frequency. When a crystal is made to vibrate at its natural frequency by the application of a voltage, the system is said to be in resonance. A crystal in resonance will maintain a constant, unfaltering frequency. When coupled with vacuum tubes or transistors, this constant frequency can be changed into a radio signal. Such was the design of the quartz radio, used primarily during World War II. Another common use of quartz is in timekeeping. All clocks rely upon some form of oscillator to keep regular time; for example, mechanical clocks sometimes use a pendulum to regulate the motion of their hands. In a quartz timepiece, a small ring-shaped piece of crystal is made to vibrate at its natural frequency. A microchip reads how many times the quartz vibrates each second and uses that information to keep accurate time. Because the crystal's vibration is unfaltering, quartz clocks are among the most precise timekeeping devices, losing less than one hundred thousandth of a second each day. Quartz crystals can be used to regulate both digital and analog clocks and watches.

Because of the many applications for quartz, the demand for clear, flawless rock crystal is often greater than the supply. Shortly after World War II, scientists developed a process by which quartz can be "grown" in the laboratory. Scientists begin with a small piece of natural crystal called a seed. Placing the seed within an alkaline solution, along with a supply of silica, they apply heat and pressure to the mixture. Slowly, the silica bonds with the seeds, eventually forming large, near-perfect crystals. Another type of man-made quartz, called fused quartz, is made by melting down many pieces of natural quartz and reforming it into almost any shape. Fused quartz displays many useful properties not found in natural quartz. First, because it neither expands nor contracts with changing temperatures, it makes an ideal component of precise scientific equipment, such as telescope and microscope lenses. It also is an unsurpassed conductor of heat, light, and ultraviolet rays , and in many cases it can be used to direct light rays through bends and angles. Additionally, fused quartz, which is nearly impervious to acids and other chemicals, is often used to make test tubes and other chemical containers.

See also Industrial minerals

quartz (rock crystal) Widely distributed rock-forming silicate mineral SiO₂ with the related semi-precious varieties rose quartz (pink), amethyst (purple), cairngorm (dark brown and similar to smoky quartz, although the original cairngorms from the Scottish mountain range were of topaz), citrine (light brown); sp. gr. 2.65; hardness 7; trigonal; commonly colourless or white, but can occur in a variety of colours; vitreous lustre; crystals usually six-sided prisms terminated by six-faced pyramids, the prisms often striated, also occurs extensively in massive form; no cleavage; conchoidal fracture; found in many igneous and metamorphic rocks, extensively in clastic rocks, and a common gangue mineral in mineral veins. See also AGATE; CHALCEDONY; COESITE; CRISTOBALITE; FLINT; JASPER; ONYX; OPAL; STISHOVITE; and TRIDYMITE.

quartz Rock-forming mineral, the natural form of silicon dioxide (silica), SiO₂. It is widely distributed, occurring in igneous and metamorphic rocks (notably granite and gneiss), and in clastic sediments. It is also found in mineral veins. It forms six-sided crystals. Pure quartz is clear and colourless but the mineral may be coloured by impurities. The most common varieties are colourless quartz (rock crystal), rose, yellow, milky, and smoky. The most usual cryptocrystalline varieties, whose crystals can be seen only under a microscope, are chalcedony and flint. Quartz crystals exhibit the piezoelectric effect and are used in electronic clocks and watches to keep accurate time. Hardness 7; r.d. 2.65.

quartz / kwôrts/ • n. a hard white or colorless mineral consisting of silicon dioxide, found widely in igneous, metamorphic, and sedimentary rocks. It is often colored by impurities (as in amethyst, citrine, and cairngorm).ORIGIN: mid 18th cent.: from German Quarz, from Polish dialect kwardy, corresponding to standard Polish twardy ‘hard.’

quartz XVIII. — (M)HG. quar(t)z; of uncert. orig.