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A very hard mineral composed of silica, SiO2, found worldwide in many different types of rocks, including sandstone and granite. Varieties of quartz include agate, chalcedony, chert, flint, opal, and rock crystal.
[German Quarz, from Middle High German quarc, of Slavic origin.]
quartzose quartz'ose' (kwôrt'sōs') adj.The most common oxide on the Earth's surface, constituting 12% of the crust by volume. Quartz is a crystalline form of silicon dioxide (SiO2). Among the igneous rocks, quartz is especially common within granites, granodiorites, pegmatites, and rhyolites. In addition, quartz can be observed in low- to high-grade metamorphic rocks, including phyllites, quartzites, schists, granulites, and eclogites. Because hydrothermal fluids are enriched in dissolved silica, the passage of fluids through rock fractures results in the emplacement of quartz veins. See also Granite; Granodiorite;
Once quartz has formed, it persists through erosional reworking because of its low solubility in water (parts per million) and its high mechanical hardness (7 on Mohs scale). Consequently, quartz becomes increasingly concentrated in beach sands as they mature, and it is a major component of sandstone. In sedimentary environments, quartz also forms as the final crystallization product during silica diagenesis; amorphous silica on the sea floor that derives from the skeletons of diatoms, radiolarians, and sponges will transform to quartz upon prolonged exposure to increased temperatures (≤300°C or 572°F) and pressures (≤2 kilobars or 200 pascals) after burial. See also Diagenesis; Hardness scales; Sandstone.
As with virtually all silicates, the atomic framework of the quartz structure consists of Si4+ cations that are tetrahedrally coordinated by oxygen anions (O2−). Every oxygen anion is bonded to two silicon cations, so that the tetrahedral units are corner-linked to form continuous chains. In low-temperature quartz (or α-quartz), two distinct tetrahedral chains spiral about the crystallographic c axis.
Although the silica tetrahedra can be depicted as spirals about the c axis in a left-handed sense, right-handed quartz crystals are found in nature as abundantly as are left-handed crystals. These enantiomorphic varieties are known as the Brazil twins of quartz, and they may be distinguished by crystal shape (corresponding crystal faces occur in different orientations) and by opposite optical activities. See also Crystal optics.
Impurity concentrations in natural α-quartz crystals usually fall below 1000 parts per million. The violet and yellow hues observed in amethyst and citrine are associated with Fe, and black smoky quartz contains Al. The white coloration of milky quartz reflects light scattering off minute fluid inclusions, and the pink tint in rose quartz is believed to arise from fine-scale intergrowths of a pegmatitic mineral called dumortierite [Al27B4Si12O69(OH)3]. See also Amethyst; Dumortierite.
Quartz is used predominantly by the construction industry as gravel and as aggregate in concrete. In addition, quartz is important in advanced technologies. Quartz is piezoelectric and has an extremely high quality factor. The high quality factor means that a bell made of quartz would resonate (ring) for a very long time. This property, combined with its piezoelectric behavior, makes quartz the perfect crystal for oscillators in watches.
Compression of α-quartz perpendicular to the c axis creates an electrostatic charge, and this property is exploited in oscillator plates in electronic components. Large flawless crystals of quartz are routinely synthesized for oscillators and for prisms in laser optic systems. Quartz also is employed in abrasives, fluxes, porcelains, and paints. See also Concrete; Oscillator; Piezoelectricity.
The graphics subsystem in the Mac OS X operating system. It provides two-dimensional drawing and windowing, and its rendering engine is based on the Adobe PDF model. See Mac OS X. See also quartz crystal.
For more information on quartz, visit Britannica.com.
Opaque white crystalline silicate stone found in many parts of the world and variously used for toolmaking and in ceremonial contexts. In Atlantic Europe white quartz pebbles were used as talismans, perhaps representing the soul of a person, from the early Neolithic through into early Christian times. White quartz is frequently found deposited around stone circle and passage grave.
Quartzite is a metamorphic rock consisting mainly of quartz which was also used for making tools and weapons, as it is hard and has conchoidal fracturing properties just like flint.
Environment
Commonest of minerals, found in every class of rocks and forming in every conceivable condition.
Crystal descriptionQuartz can be divided into two groups on the basis of its appearance: crystallized and microcrystalline. The microcrystalline group can in turn be subdivided into a parallel, fibrous crystal arrangement and a heterogeneous, finely granular type.
1. Crystallized quartz often occurs in large, well-formed, colorless crystals or crystal crusts, often transparent and gemmy. Colorless crystals are known as rock crystal. Violet crystals are known as amethyst. Yellow-brown crystals are known as citrine. Gray to black crystals are known as smoky quartz. Also forms veins or central cores in pegmatites of coarsely crystallized material, which may be milky quartz or rose quartz.
2a. Chalcedony is a microscopically crystallized, translucent variety of the same mineral, in which layers of microscopic individual crystals have arranged themselves as layers of slender upright fibers arranged in parallel bands. The upper surface of a chalcedony-lined pocket tends to be botryoidal or mammillary, and is often uniformly smooth. White or cloudy banding irregularities commonly develop on cross-fractured weathering surfaces. In agate, the banding is colored and penetrating, often making a series of concentric rings lining geodes.
2b. The chert, flint, and jasper group are also tight and hard, microscopically grained quartz, but in these there is no definite banding nor translucency. They form dull-surfaced opaque masses. Usually chert and jasper have appreciable quantities of impurities, with lusters ranging from earthy to sub-glassy (flint) to matte. Jasper is often colorful, tinted by ocher or hematite.
Massive white quartz chunks, sometimes with gold, can originate in solid veins that slash older rocks. Massive quartz, quartz sand, and disseminated grains of quartz in other rocks, or in pebbles of quartz or quartzite, are very common, and usually are the most important constituents of any gravel or sand beach.
Free-growing quartz crystals vary in habit from long slender prisms to crusts or "points." Prism faces are usually horizontally striated; six terminal faces usually exhibit alternating development of larger and smaller faces (indicating the rhombohedral rather than a hexagonal symmetry). More than a thousand differently indexed faces have been described (on alphaquartz, see below).
Because of the composition, quartz and the other SiO 2 minerals, cristobalite, tridymite, and coesite were long grouped with the oxides, but their physical properties and crystal structure are more in accord with those of the silicate group, so it now seems appropriate to group them as silicates. Quartz itself has several crystal-class modifications, and although it has only right- or left-hand rhombohedral symmetry at normal temperatures, it is fully developed or paired rhombohedral at temperatures above 573°C. This higher symmetry form is known as beta-quartz (ȣ-quartz), and only forms when quartz crystallizes from truly hot solutions. However, after crystallizing -- as its surroundings cool below 573°C -- the structure then changes to alpha-quartz (ᅣ-quartz), and all quartz that we find in our temperate surroundings is of course ᅣ-quartz. Quartz has been useful as a geological thermometer, because the habit it assumes sometimes indicates whether it formed above or below 573°C.
Two chemically identical minerals to be described following quartz carry geological thermometry higher. SiO 2 crystallizing above 870°C forms platy orthorhombic crystals of a mineral known as tridymite (TRID ih mite) . Crystallizing above 1470°C, SiO 2 forms in white cubic-system crystals and is known as cristobalite. Hence, from the series of differently crystallizing compounds of this fortunately common substance, we can deduce the temperature of the formation of many rocks. The two high-temperature SiO 2 compounds are rarer than might be expected, for in solidifying, cooling rocks stay liquid down to far lower temperatures expected if we were to judge by the heat that is required to remelt them, once they have recrystallized. Under some conditions it is thought that tridymite and cristobalite can form at temperatures slightly lower than those at which they are really stable.
Physical propertiesColorless, white, smoky, rose, violet, green, yellow and brown; also translucent and tinted any hue by impurities. Luster glassy; hardness 7; specific gravity 2.6; fracture conchoidal (irregular for microcrystalline); cleavage rhombohedral, sometimes observable. Large crystals brittle, microcrystalline varieties tough to very tough; transparent to subtranslucent from impurities. Rock crystal often triboluminescent; electrically responsive to pressure (piezoelectric) and current; irradiation will make aluminous rock crystal smoky, and subsequent heating will then turn some examples yellow.
CompositionSilicon dioxide (46.7% Si, 53.3% O).
TestsInfusible (before the blowpipe; it melts at 1720°C), insoluble. The hardness of 7 is important. Powder mixed with sodium carbonate fuses to a clear glass.
Distinguishing characteristicsThe luster and fracture are typical, together with a hardness greater than that of most similar minerals. Crystals are easy to recognize if the hexagonal pattern (of usually alternating larger and smaller triangular faces) or the typical points can be seen. Horizontal striations on the prism are very helpful. Specific gravity is a useful test for this mineral. A crystal flake held in gas flame flies to pieces (as soon as it reaches 573°C). White beryl just frosts but stays intact, white topaz has a ready cleavage. On a diamond saw, a groove being cut in rock crystal shows an orange glow of constant sparking.
OccurrenceQuartz can occur almost anywhere. High-temperature veins are usually coarsely crystallized, whereas low-temperature veins and geodes in sedimentary rocks may be lined with crystals or show one of the finer-grained varieties.
Veins with colorless crystals of "rock crystal" are abundant everywhere: in Arkansas in the Hot Springs area; at Little Falls, New York, in small, brilliant, doubly terminated crystals ("Herkimer diamonds"); in Ontario near Lyndhurst. The smoky crystals of the Pikes Peak area of Colorado are often spectacular, and some fine crystals have come from the Maine and the California pegmatite areas. Foreign localities include the famous Alpine crystal-lined pocket occurrences (it seems that the higher their discovery elevation, the smokier their crystals) and the commercially important Madagascar and Brazilian rock crystals.
Beautiful amethyst is just too common to be in the precious category. It is found in Maine, Pennsylvania, Virginia, North Carolina, along the north shore of Lake Superior (Thunder Bay), Arizona, and elsewhere in the U.S. The purple variety is more often in points than in tall prismatic crystals, but Mexico is the home of two fine prismatic sources, one in Guerrero (veins) with steep rhombohedron faces, and a second at Las Vegas, in the state of Vera Cruz (pockets in andesitic lava). Bahia and Rio Grande do Sul are the two important amethyst-producing states in Brazil; also in neighboring Uruguay and Bolivia. For many years an occurrence in Kapnik, Hungary, was about the only known site for elongated amethysts; almost all the South American specimens were groups of points.
Citrine quartz is naturally yellow, but rather uncommon. An occurrence of internally gemmy, though superficially ugly, frosted prisms in veins in granite at Villasbuenos, Salamanca, Spain was the original site for "Spanish Topaz," long a popular jewelers' name for citrine. With heat of around 400-500°C, Brazilian amethysts bleach, and above 500°C (but under 573°C) turn golden to brown; others show green after such treatment. A combination, now called ametrine, which has citrine and amethyst sections in the same crystal, has been found in southern Bolivia. Irradiation turns heated amethyst-citrines back to amethyst, but ametrine appears to be natural
Slightly cloudy rose quartz, perhaps with microcrystalline rutile, is a pegmatite mineral often occupying the quartz core of a pegmatite. Pink crystals are scarce; token ones were found long ago at Newry, Maine, and more spectacular ones at two Brazilian localities. The failure to find large, well-formed crystals of rose quartz is a geological mystery, and even now there seem to be some possibly basic differences between the common solid rose quartz of pegmatite cores and the three occurrences of pink-hued, slightly cloudy, late-formed crystals often associated with pink chalcedony. Sapucaia and Taquaral in Minas Gerais, Brazil, have produced some beautiful specimens of pink crystals. Glass-clear pink bands have been noted in some Brazilian rock crystals but have not yet been studied.
Smoky quartz appears to have been naturally irradiated aluminum-bearing material. It is common in the Alps; there seems a relationship between the elevation of the source and the blackness of the crystals.
The best agate forms in cavities in basaltic rock, as in the w. U.S., northern Mexico, and in Rio Grande do Sul, Brazil, the chief source of commercial agate. The famous Idar gemcutting industry of Germany owes its start to the occurrence there of agate concretions in neighboring lava flows. Queensland, Australia has fine small agate nodules and much of the jadelike green chalcedony called chrysoprase.
While we prefer to designate as agate the abundant Brazilian banded material, the word is loosely used and often applied to nonbanded material, as in the dendritic black-stained chalcedony known as Montana agate, the green and red "moss"-saturated chalcedony known as moss agate, and the jasperized (inappropriately called agatized) Arizona petrified wood. There are various opaque microcrystalline examples. Bloodstone, for example, seems to be a moss agate so full of green and hematite specks, that it approaches jasper's opacity. Microcrystalline quartz that forms pseudomorphs after asbestos fibers can be cut into chatoyant stones known as "tiger eye." Similar material rich in red hematite is found in Australia and sold as "tiger iron."
Whole books have been written on quartz and its relatives. Volume 3 of the seventh edition of Dana is devoted to SiO 2 .
RemarksAn important industrial material from many standpoints. Sand is used in glass manufacture or to make fused silica. The clear rock crystal is of great value in electronic equipment, as in oscillators for controlling radio frequencies and in watches. The beautifully colored varieties have gem value. Rose quartz often shows asterism when cut in a sphere or hemisphere. White quartz veins are common guides to gold in some regions. Chalcedony and agate, which can be dyed in rainbow hues for decorative use, are also of value for bearings and in mortars. Flint, for which the Dover Cliffs are famous, is a gray to black, subvitreous and compact variety once valued for the sparks it gave when struck by steel. Chrysoprase is a natural, nickel-stained green chalcedony but it is perfectly duplicated with dyes in Idar Oberstein, Germany. Simple "onyx" is a dyed-black chalcedony (not to be confused with banded calcite onyx of cave and hot spring deposits). There is a rainbow of other dyed chalcedony-onyxes. Chert, the common light-colored nodule quartz in Midwest limestones, was used for arrowheads. Jasper is usually darker and more opaque and may contain as much as 20 percent impurities such as hematite and goethite. When fairly pure it can be very, very tough and has been used in ball mills for crushing sulfide ores. Cryptocrystalline (microcrystalline) quartz is a favorite medium for the gem carvers of Idar Oberstein, which owes its preeminence to the once-abundant agate mined in the hills and contained in stream cobbles.
Miners look for specific kinds of quartz in order to locate possible sources for gold.
| Quartz | |
|---|---|
 |
|
| General | |
| Category | Mineral |
| Chemical formula | Silica (silicon dioxide, SiO2) |
| Identification | |
| Color | Clear (if no impurities); also see Varieties |
| Crystal habit | 6-sided prism ending in 6-sided pyramid (typical) |
| Crystal system | rhombohedral class 32 |
| Twinning | Dauphine law, Brazil law and Japan law |
| Cleavage | None |
| Fracture | Conchoidal |
| Mohs Scale hardness | 7 - lower in impure varieties |
| Luster | Vitreous/glossy |
| Refractive index | nω = 1.543 - 1.545 nε = 1.552 - 1.554 |
| Optical Properties | Uniaxial (+) |
| Birefringence | +0.009 (B-G interval) |
| Pleochroism | None |
| Streak | White |
| Specific gravity | 2.65 constant; variable in impure varieties |
| Melting point | 1650 (±75) °C |
| Solubility | H2O insoluble |
| Diaphaneity | Transparent to translucent |
| Other Characteristics | Piezoelectric |
Quartz (from German 
Quarz?[1]) is the second most common mineral in the Earth's continental crust, feldspar being the first. It is made up of a lattice of
silica (SiO2) tetrahedra. Quartz has a hardness of 7 on the
Mohs scale and a density of 2.65
g/cm³.
Quartz belongs to the rhombohedral 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, 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, but because the crystals must be attached at the other end to a matrix, only one termination pyramid is present. A quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward.
Quartz goes by an array of different names. 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). Chalcedony is a generic term for cryptocrystalline quartz. The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline.
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. This does not always hold true.
Not all varieties of quartz are naturally occurring. 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-treated amethyst. Carnelian is widely heat-treated to deepen its color.
Because natural quartz is so often twinned, much quartz used in industry is synthesized. Large, flawless and untwinned crystals are produced in an autoclave via the hydrothermal process: emeralds are also synthesized in this fashion.
Quartz occurs in hydrothermal veins and pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. These veins may bear precious metals such as gold or silver, and form the quartz ores sought in mining. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals."
Quartz is a common constituent of
| Chalcedony | Any cryptocrystalline quartz, although generally only used for white or lightly coloured material. Otherwise more specific names are used. |
| Agate | Multi-coloured, banded Chalcedony, semi-translucent to translucent |
| Onyx | Agate where the bands are straight, parallel and consistent in size. |
| Jasper | Opaque chalcedony, impure |
| Aventurine | Translucent chalcedony with small inclusions (usually mica) that shimmer. |
| Tiger's eye | Fibrous gold to red-brown coloured quartz, exhibiting chatoyancy. |
| Rock crystal or mountain crystal | Clear, colourless |
| Amethyst | Purple, transparent |
| Citrine | Yellow to reddish orange to brown, greenish yellow |
| Prasiolite | Mint green, transparent |
| Rose quartz | Pink, translucent, may display diasterism |
| Milk quartz or snow quartz | White, translucent to opaque, may display diasterism |
| Smoky quartz | Brown to grey, opaque |
| Morion | Dark-brown, opaque |
| Carnelian | Reddish orange chalcedony, translucent |
Tridymite and cristobalite are high-temperature polymorphs of SiO2 that occur in high-silica volcanic rocks. Coesite is a denser polymorph of quartz 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 quartz found in some meteorite impace sites. Lechatelierite is an amorphous silica glass SiO2 which is formed by lightning strikes in quartz sand.
The name "quartz" comes from the German "Quarz", which is of Slavic origin (Czech miners called it křemen). Other sources insist the name is from the Saxon word "Querkluftertz", meaning cross-vein ore.[2]
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, eg. Newgrange or Carrowmore in Ireland. The Irish word for quartz is grian cloch, which means 'stone of the sun'.
Roman naturalist Pliny the Elder believed quartz to be water ice, permanently frozen after great lengths of time. (The word "crystal" comes from the Greek word for ice.) He supported this idea by saying that quartz is found near glaciers in the Alps, but not on volcanic mountains, and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of the ability of quartz to split light into a spectrum. This idea persisted until at least the 1600s.
Nicolas Steno's study of quartz paved the way for modern crystallography. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60 degree angle.
Charles Sawyer invented the commercial quartz crystal manufacturing process in Cleveland, OH. This initiated the transition from mined and cut quartz for electrical appliances to manufactured quartz.
The quartz oscillator or resonator was first developed by Walter Guyton Cady in 1921 [2]. George Washington Pierce designed and patented quartz crystal oscillators in 1923 [3]. Warren Marrison created the first quartz oscillator clock based on the work of Cady and Pierce in 1927 [4].
Quartz crystals are rotary polar (see rotary polarization) and have the ability to rotate the plane of polarization of light passing through them. They are also highly piezoelectric, becoming polarized with a negative charge on one end and a positive charge on the other when subjected to pressure. They will vibrate if an alternating electric current is applied to them. This proves them to be highly important in commerce for making pressure gauges, oscillators, resonators and watches.
Quartz crystals have piezoelectric properties, that is they generate an electric current 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 perhaps the most familiar device using the mineral. The same principle is also used for very accurate measurements of very small mass changes by means of the quartz crystal microbalance.
| Gemstones and crystals | |
|---|---|
| Gems: | Aquamarine · Emerald · Garnet · Jasper · Lapis lazuli · Pearl · Peridot · Ruby · Sunstone · Tiger's eye |
| Crystals: | Agate · Amethyst · Chalcedony · Diamond · Pyrite · Quartz · Rhodochrosite · Sapphire · Topaz · Tourmaline |
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
idioms:
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Ελληνική (Greek)
n. - (ορυκτολ.) χαλαζίας
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Português (Portuguese)
n. - quartzo (m) (Min.)
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中文（简体） (Chinese (Simplified))
石英
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中文（繁體） (Chinese (Traditional))
n. - 石英
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日本語 (Japanese)
n. - 石英, クォーツ, 水晶
idioms:
العربيه (Arabic)
(الاسم) مرو, الكوارتس, بلور
עברית (Hebrew)
n. - קוורץ (מינרל)
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