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Quartz is a hard mineral composed of silica (silicon dioxide). Its are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen atom being shared between two tetrahedra, giving an overall chemical formula of Silicon dioxide. Therefore, quartz is classified structurally as a framework silicate mineral and compositionally as an oxide mineral. Quartz is the second most common mineral or mineral group in Earth's lithosphere, comprising about 12% by mass.
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 . Since the transformation is accompanied by a significant change in volume, it can easily induce microfracturing of ceramics or rocks passing through this temperature threshold.
There are many different varieties of quartz, several of which are classified as . Since antiquity, varieties of quartz have been the most commonly used minerals in the making of Jewellery and hardstone carvings, especially in Europe and Asia.
Quartz is the mineral defining the value of 7 on the Mohs scale of hardness, a qualitative Scratch hardness method for determining the hardness of a material to abrasion.
The Ancient Greece referred to quartz as κρύσταλλος () meaning "crystal", derived from the Ancient Greek κρύος () meaning "icy cold", because some (including Theophrastus) believed the mineral to be a form of supercooled ice. Today, the term Crystal is sometimes used as an alternative name for transparent, coarsely crystalline quartz. (2026). 9780195106916, Oxford University Press. ISBN 9780195106916
In the 17th century, Nicolas Steno's study of quartz paved the way for modern crystallography. He discovered that, regardless of a quartz crystal's size or shape, its long prism faces always meet at a perfect 60° angle, thereby establishing the law of constancy of interfacial angles.Nicolaus Steno (Latinized name of Niels Steensen) with John Garrett Winter, trans.. The Prodromus of Nicolaus Steno's Dissertation Concerning a Solid Body Enclosed by Process of Nature Within a Solid (New York, New York: Macmillan Co., 1916). On page 272 , Steno states his law of constancy of interfacial angles: "Figures 5 and 6 belong to the class of those which I could present in countless numbers to prove that in the plane of the axis both the number and the length of the sides are changed in various ways without changing the angles; … "
Both polymorphs of quartz can occur in two different depending on the chirality. Above the transition temperature, α-quartz in P3121 (space group 152) becomes β-quartz in P6422 (space group 181), and α-quartz in P3221 (space group 154) becomes β-quartz in P6222 (space group 180).Crystal Data, Determinative Tables, ACA Monograph No. 5, American Crystallographic Association, 1963
These space groups are truly chiral (they each belong to the 11 enantiomorphous pairs). Both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks (SiO4 tetrahedra in the present case). The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, without a change in the way they are linked. However, there is a significant change in volume during this transition, and this can result in significant microfracturing in ceramics during firing, in ornamental stone after a fire and in rocks of the Earth's crust exposed to high temperatures, thereby damaging materials containing quartz and degrading their physical and mechanical properties.
The crystal habit for quartz is a six-sided prism terminating with six-sided pyramid-like at each end. In nature, quartz crystals are often Crystal twinning (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 as a druse (a layer of crystals lining a void), of which quartz are particularly fine examples.
Quartz varieties were previously classified into three categories based on the visibility of their individual crystals. Macrocrystalline quartz varieties have individual crystals that are visible to the unaided eye (macroscopic). Microcrystalline quartz varieties are aggregates of tiny crystals that can only be seen through a microscope (microscopic). Cryptocrystalline quartz varieties are aggregates of crystals that are too small to be seen even with an optical microscope (sub-microscopic). Today, the microcrystalline and cryptocrystalline varieties are commonly grouped together and referred to as chalcedony. However, in the scientific literature, chalcedony is a specific form of silica consisting of fine intergrowths of both quartz and its monoclinic polymorph, moganite. Chalcedony is commonly translucent to opaque, while the macrocrystalline varieties of quartz tend to be more transparent. Color is a secondary identifier for the cryptocrystalline varieties and a primary identifier for the macrocrystalline varieties.
While the majority of quartz crystallizes from molten magma, quartz also chemically precipitates from hot hydrothermal veins as gangue, sometimes with ore minerals such as gold, silver and copper. Large crystals of quartz are found in magmatic . Well-formed crystals may reach several meters in length and mass hundreds of kilograms.
The largest documented single crystal of quartz was found near Itapore, Goyaz, Brazil; it measured approximately and weighed over .
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 has been heat-treated to deepen its color since prehistoric times.
Because natural quartz is often crystal twinning, 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.
While jade has been the most prized semi-precious stone for carving in East Asia and pre-Columbian America since earliest times, in Europe and the Middle East different varieties of quartz were the most commonly used for the various types of Jewellery and hardstone carving, including and cameo gems, rock crystal vases, and extravagant vessels. The tradition continued to produce highly valued objects until the mid-19th century, when it largely fell from fashion except in jewelry. Cameo technique exploits the bands of color in onyx and other varieties.
Efforts to synthesize quartz began in the mid-19th century as scientists attempted to create minerals under laboratory conditions that mimicked the conditions in which the minerals formed in nature. German geologist Karl Emil von Schafhäutl (1803–1890) was the first person to synthesize quartz when in 1845 he created microscopic quartz crystals in a Pressure cooking. From page 578: 5) Bildeten sich aus Wasser, in welchen ich im Papinianischen Topfe frisch gefällte Kieselsäure aufgelöst hatte, beym Verdampfen schon nach 8 Tagen Krystalle, die zwar mikroscopisch, aber sehr wohl erkenntlich aus sechseitigen Prismen mit derselben gewöhnlichen Pyramide bestanden. ( 5) There formed from water in which I had dissolved freshly precipitated silicic acid in a Papin pot i.e.,, after just 8 days of evaporating, crystals, which albeit were microscopic but consisted of very easily recognizable six-sided prisms with their usual pyramids.) However, the quality and size of the crystals that were produced by these early efforts were poor.Byrappa, K. and Yoshimura, Masahiro (2001) Handbook of Hydrothermal Technology. Norwich, New York: Noyes Publications. . Chapter 2: History of Hydrothermal Technology.
Elemental impurity incorporation strongly influences the ability to process and utilize quartz. Naturally occurring quartz crystals of extremely high purity, necessary for the crucibles and other equipment used for growing perfect large silicon boules to be sliced into silicon wafers in the semiconductor industry, are expensive and rare. These high-purity quartz are defined as containing less than 50 ppm of impurity elements. A major mining location for high-purity quartz is the Spruce Pine Mining District in Spruce Pine, North Carolina, United States. Quartz may also be found in Caldoveiro Peak in Asturias, Spain.
By the 1930s, the electronics industry had become dependent on quartz crystals. The only source of suitable crystals was Brazil; however, World War II disrupted supplies from Brazil, so nations attempted to synthesize quartz on a commercial scale. German mineralogist Richard Nacken (1884–1971) achieved some success during the 1930s and 1940s.Nacken, R. (1950) "Hydrothermal Synthese als Grundlage für Züchtung von Quarz-Kristallen" (Hydrothermal synthesis as a basis for the production of quartz crystals), Chemiker Zeitung, 74 : 745–749. After the war, many laboratories attempted to grow large quartz crystals. In the United States, the U.S. Army Signal Corps contracted with Bell Labs and with the Brush Development Company of Cleveland, Ohio to synthesize crystals following Nacken's lead. (Prior to World War II, Brush Development produced piezoelectric crystals for record players.) By 1948, Brush Development had grown crystals that were 1.5 inches (3.8 cm) in diameter, the largest at that time. "Record crystal", Popular Science, 154 (2) : 148 (February 1949).Brush Development's team of scientists included: Danforth R. Hale, Andrew R. Sobek, and Charles Baldwin Sawyer (1895–1964). The company's U.S. patents included:
An early use of the piezoelectricity of quartz crystals was in phonograph pickups. One of the most common piezoelectric uses of quartz today is as a crystal oscillator. Also called a quartz oscillator or resonator, it was first developed by Walter Guyton Cady in 1921. George Washington Pierce designed and patented quartz crystal oscillators in 1923.Pierce, George W. "Electrical system", , filed: 25 February 1924; issued: 18 October 1938. The quartz clock is a familiar device using the mineral; it is simply a clock that uses a quartz oscillator as its time reference. Warren Marrison created the first quartz oscillator clock based on the work of Cady and Pierce in 1927. 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. (NB. This was partially presented at Physikertagung in Heidelberg in October 1957.)
Almost all the industrial demand for quartz crystal (used primarily in electronics) is met with synthetic quartz produced by the hydrothermal process. However, synthetic crystals are less prized for use as gemstones. The popularity of crystal healing has increased the demand for natural quartz crystals, which are now often mined in developing countries using primitive mining methods, sometimes involving child labor.
(1964). 9780442276249, Van Nostrand. ISBN 9780442276249 The crystals are attached at one end to the enclosing rock, and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, for instance, within gypsum.
Varieties
Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent. Colored varieties of quartz are common and 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, emitting colored light.
+ Varieties of quartz (2026). 9781770856448, Firefly Books. ISBN 9781770856448 Milky quartz at Mineral Galleries . Galleries.com. Retrieved 2013-03-07.
Piezoelectricity
Quartz crystals have piezoelectricity properties; they develop an electric potential upon the application of mechanical stress. (2026). 9780081021354, Woodhead Publishing. ISBN 9780081021354 Quartz's piezoelectric properties were discovered by Jacques Curie and Pierre Curie in 1880.. Reprinted in:
Occurrence
Quartz is the second most abundant mineral or mineral group in the Earth's lithosphere; by mass, the feldspar group comprises 41% of the lithosphere, followed by quartz at 12% and the pyroxene group at 11%.
Quartz is a defining constituent of granite and other felsic . It is very common in such as sandstone and shale. It is a common constituent of schist, gneiss, quartzite and other . 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 . 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. (2026). 9780131547285, Pearson Prentice Hall. ISBN 9780131547285
Mining
Quartz is extracted from Open-pit mining. Miners occasionally use explosives to expose deep pockets of quartz. More frequently, and are used to remove soil and clay and expose quartz veins, which are then worked using hand tools. Care must be taken to avoid sudden temperature changes that may damage the crystals.
Related silica minerals
Tridymite and cristobalite are high-temperature polymorphs of SiO2 that occur in high-silica Volcano rocks. Coesite is a denser polymorph of SiO2 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 SiO2 found in some meteorite impact sites. Moganite is a monoclinic polymorph. Lechatelierite is an Amorphous solid silica glass SiO2 which is formed by lightning strikes in quartz sand.
Safety
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.
Synthetic and artificial treatments
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.Liccini, Mark, Treating Quartz to Create Color , International Gem Society website. Retrieved 22 December 2014
Robert Webster, Michael O'Donoghue (2006). 9780750658560, Butterworth-Heinemann. . ISBN 9780750658560
Uses
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. Quartz was also used in prehistoric Ireland, as well as many other countries, for ; both vein quartz and rock crystal were knapping as part of the lithic technology of prehistoric peoples.
By the 1950s, hydrothermal synthesis techniques were producing synthetic quartz crystals on an industrial scale, and today virtually all the quartz crystal used in the modern electronics industry is synthetic.
See also
External links
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