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Quartz is a hard, crystalline mineral composed of silicon and oxygen atoms. The atoms are linked in a continuous framework of SiO 4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO 2 . Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar. Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation from α-quartz to β-quartz takes place abruptly at 573 °C (846 K; 1,063 °F). Since the transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature threshold. There are many different varieties of quartz, several of which are semi-precious gemstones. Since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. Quartz is the mineral de

The word "quartz" is derived from the German word "Quarz", which had the same form in the first half of the 14th century in Middle High German and in East Central German and which came from the Polish dialect term kwardy , which corresponds to the Czech term tvrdý ("hard"). The Ancient Greeks referred to quartz as κρύσταλλος ( krustallos ) derived from the Ancient Greek κρύος ( kruos ) meaning "icy cold", because some philosophers (including Theophrastus) apparently believed the mineral to be a form of supercooled ice. Today, the term rock crystal is sometimes used as an alternative name for the purest form of quartz.

Quartz belongs to the trigonal crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end. In nature quartz crystals are often twinned (with twin right-handed and left-handed quartz crystals), distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. Well-formed crystals typically form in a 'bed' that has unconstrained growth into a void; usually the crystals are attached at the other end to a matrix, and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, for instance, within gypsum. A quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the trigonal crystal system, space group P 3 1 21 or P 3 2 21 depending on the chirality. β-q

Although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Major varieties of quartz Type Color & Description Transparent Herkimer diamond Colorless Transparent Rock crystal Colorless Transparent Amethyst Purple to violet colored quartz Transparent Citrine Yellow quartz ranging to reddish orange or brown, and occasionally greenish yellow Transparent Ametrine A mix of amethyst and citrine with hues of purple/violet and yellow or orange/brown Transparent Rose quartz Pink, may display diasterism Transparent Chalcedony Fibrous, variously translucent, cryptocrystalline quartz occurring in many varieties. The term is often used for white, cloudy, or lightly colored material intergrown with moganite. Ot

Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, and has often been used for hardstone carvings, such as the Lothair Crystal. Common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. These color differentiations arise from the presence of impurities which change the molecular orbitals, causing some electronic transitions to take place in the visible spectrum causing colors. Polymorphs of quartz include: α-quartz (low), β-quartz, tridymite, moganite, cristobalite, coesite, and stishovite. The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony i

Not all varieties of quartz are naturally occurring. Some clear quartz crystals can be treated using heat or gamma-irradiation to induce color where it would not otherwise have occurred naturally. Susceptibility to such treatments depends on the location from which the quartz was mined. Prasiolite, an olive colored material, is produced by heat treatment; natural prasiolite has also been observed in Lower Silesia in Poland. Although citrine occurs naturally, the majority is the result of heat-treating amethyst or smoky quartz. Carnelian is widely heat-treated to deepen its color. Because natural quartz is often twinned, synthetic quartz is produced for use in industry. Large, flawless, single crystals are synthesized in an autoclave via the hydrothermal process. Like other crystals, quartz may be coated with metal vapors to give it an attractive sheen.

Quartz is a defining constituent of granite and other felsic igneous rocks. It is very common in sedimentary rocks such as sandstone and shale. It is a common constituent of schist, gneiss, quartzite and other metamorphic rocks. Quartz has the lowest potential for weathering in the Goldich dissolution series and consequently it is very common as a residual mineral in stream sediments and residual soils. Generally a high presence of quartz suggests a "mature" rock, since it indicates the rock has been heavily reworked and quartz was the primary mineral that endured heavy weathering. While the majority of quartz crystallizes from molten magma, quartz also chemically precipitates from hot hydrothermal veins as gangue, sometimes with ore minerals like gold, silver and copper. Large crystals of quartz are found in magmatic pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. Naturally occurring quartz crystals of extremely high purit

Quartz is extracted from open pit mines. Miners only use explosives on rare occasions when they need to expose a deep seam of quartz. The reason for this is that although quartz is known for its hardness, it damages easily if it is suddenly exposed to a change in temperature, such as that caused by a blast. Instead, mining operations use bulldozers and backhoes to remove soil and clay, and expose the quartz crystal veins in the rock.

Tridymite and cristobalite are high-temperature polymorphs of SiO 2 that occur in high-silica volcanic rocks. Coesite is a denser polymorph of SiO 2 found in some meteorite impact sites and in metamorphic rocks formed at pressures greater than those typical of the Earth's crust. Stishovite is a yet denser and higher-pressure polymorph of SiO 2 found in some meteorite impact sites. Lechatelierite is an amorphous silica glass SiO 2 which is formed by lightning strikes in quartz sand.

As quartz is a form of silica, it is a possible cause for concern in various workplaces. Cutting, grinding, chipping, sanding, drilling, and polishing natural and manufactured stone products can release hazardous levels of very small, crystalline silica dust particles into the air that workers breathe. Crystalline silica of respirable size is a recognized human carcinogen and may lead to other diseases of the lungs such as silicosis and pulmonary fibrosis.

The word "quartz" comes from the German Quarz   ( help · info ) , which is of Slavic origin (Czech miners called it křemen ). Other sources attribute the word's origin to the Saxon word Querkluftertz , meaning cross-vein ore . Quartz is the most common material identified as the mystical substance maban in Australian Aboriginal mythology. It is found regularly in passage tomb cemeteries in Europe in a burial context, such as Newgrange or Carrowmore in Ireland. The Irish word for quartz is grianchloch , which means 'sunstone'. Quartz was also used in Prehistoric Ireland, as well as many other countries, for stone tools; both vein quartz and rock crystal were knapped as part of the lithic technology of the prehistoric peoples. While jade has been since earliest times the most prized semi-precious stone for carving in East Asia and Pre-Columbian America, in Europe and the Middle East the different varieties of quartz were the most commonly used for the various types

Some types of quartz crystals have piezoelectric properties; they develop an electric potential upon the application of mechanical stress. An early use of this property of quartz crystals was in phonograph pickups. One of the most common piezoelectric uses of quartz today is as a crystal oscillator. The quartz clock is a familiar device using the mineral. The resonant frequency of a quartz crystal oscillator is changed by mechanically loading it, and this principle is used for very accurate measurements of very small mass changes in the quartz crystal microbalance and in thin-film thickness monitors.