| Formula |
|Strunz classification||4.DA.05 (Oxides)|
|Dana classification||75.01.03.01 (tectosilicates)|
|Crystal system||α-quartz: trigonal |
|Crystal class||α-quartz: trapezohedral (class 3 2); β-quartz: trapezohedral (class 6 2 2)|
|Unit cell||a = 4.9133 Å, c = 5.4053 Å; Z=3|
|Formula mass||60.083 g·mol−1|
|Color||Colorless through various colors to black|
|Crystal habit||6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive|
|Twinning||Common Dauphine law, Brazil law and Japan law|
|Mohs scale hardness||7 – lower in impure varieties (defining mineral)|
|Luster||Vitreous – waxy to dull when massive|
|Diaphaneity||Transparent to nearly opaque|
|Specific gravity||2.65; variable 2.59–2.63 in impure varieties|
|Optical properties||Uniaxial (+)|
|Refractive index||nω = 1.543–1.545 |
nε = 1.552–1.554
|Birefringence||+0.009 (B-G interval)|
|Melting point||1670 °C (β tridymite) 1713 °C (β cristobalite)|
|Solubility||Insoluble at STP; 1 ppmmass at 400 °C and 500 lb/in2 to 2600 ppmmass at 500 °C and 1500 lb/in2|
|Other characteristics||lattice: hexagonal, Piezoelectric, may be triboluminescent, chiral (hence optically active if not racemic)|
Quartz is a hard, crystalline mineral composed of silicon and oxygen atoms. The atoms are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. 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.
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 in East Central Germanand 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 P3121 or P3221 depending on the chirality. β-quartz belongs to the hexagonal system, space group P6222 and P6422, respectively.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 change in the way they are linked.
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.
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 chromophores which have been incorporated into the crystal structure of the mineral. 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 is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite.Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, and jasper.
Amethyst is a form of quartz that ranges from a bright vivid violet to dark or dull lavender shade. The world's largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia and Morocco. Sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine. An amethyst is formed when there is iron in the area where it was formed.
Blue quartz contains inclusions of fibrous magnesio-riebeckite or crocidolite.
Inclusions of the mineral dumortierite within quartz pieces often result in silky-appearing splotches with a blue hue, shades giving off purple and/or grey colors additionally being found. "Dumortierite quartz" (sometimes called "blue quartz") will sometimes feature contrasting light and dark color zones across the material.Interest in the certain quality forms of blue quartz as a collectible gemstone particularly arises in India and in the United States.
Citrine is a variety of quartz whose color ranges from a pale yellow to brown due to ferric impurities. Natural citrines are rare; most commercial citrines are heat-treated amethysts or smoky quartzes. However, a heat-treated amethyst will have small lines in the crystal, as opposed to a natural citrine's cloudy or smokey appearance. It is nearly impossible to differentiate between cut citrine and yellow topaz visually, but they differ in hardness. Brazil is the leading producer of citrine, with much of its production coming from the state of Rio Grande do Sul. The name is derived from the Latin word citrina which means "yellow" and is also the origin of the word "citron". Sometimes citrine and amethyst can be found together in the same crystal, which is then referred to as ametrine.Citrine has been referred to as the "merchant's stone" or "money stone", due to a superstition that it would bring prosperity.
Citrine was first appreciated as a golden-yellow gemstone in Greece between 300 and 150 BC, during the Hellenistic Age. The yellow quartz was used prior to that to decorate jewelry and tools but it was not highly sought after.
Milk quartz or milky quartz is the most common variety of crystalline quartz. The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation,making it of little value for optical and quality gemstone applications.
Rose quartz is a type of quartz which exhibits a pale pink to rose red hue. The color is usually considered as due to trace amounts of titanium, iron, or manganese, in the material. Some rose quartz contains microscopic rutile needles which produces an asterism in transmitted light. Recent X-ray diffraction studies suggest that the color is due to thin microscopic fibers of possibly dumortierite within the quartz.
Additionally, there is a rare type of pink quartz (also frequently called crystalline rose quartz) with color that is thought to be caused by trace amounts of phosphate or aluminium. The color in crystals is apparently photosensitive and subject to fading. The first crystals were found in a pegmatite found near Rumford, Maine, US and in Minas Gerais, Brazil.
Smoky quartz is a gray, translucent version of quartz. It ranges in clarity from almost complete transparency to a brownish-gray crystal that is almost opaque. Some can also be black. The translucency results from natural irradiation creating free silicon within the crystal.
Prasiolite, also known as vermarine, is a variety of quartz that is green in color. Since 1950, almost all natural prasiolite has come from a small Brazilian mine, but it is also seen in Lower Silesia in Poland. Naturally occurring prasiolite is also found in the Thunder Bay area of Canada. It is a rare mineral in nature; most green quartz is heat-treated amethyst.
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; emeralds are also synthesized in this fashion.
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.
While the majority of quartz crystallizes from molten magma, much 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 purity, necessary for the crucibles and other equipment used for growing silicon wafers in the semiconductor industry, are expensive and rare. A major mining location for high purity quartz is the Spruce Pine Gem Mine in Spruce Pine, North Carolina, United States.Quartz may also be found in Caldoveiro Peak, in Asturias, Spain.
The largest documented single crystal of quartz was found near Itapore, Goiaz, Brazil; it measured approximately 6.1×1.5×1.5 m and weighed 39,916 kilograms.
Tridymite and cristobalite are high-temperature polymorphs of SiO2 that occur in high-silica volcanic 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. Lechatelierite is an amorphous silica glass SiO2 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
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 of jewelry and hardstone carving, including engraved gems and cameo gems, rock crystal vases, and extravagant vessels. The tradition continued to produce objects that were very highly valued 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.
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 κρύσταλλος, "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. This idea persisted until at least the 17th century. He also knew of the ability of quartz to split light into a spectrum.
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 joined at a perfect 60° angle.
Quartz's piezoelectric properties were discovered by Jacques and Pierre Curie in 1880.The quartz oscillator or resonator was first developed by Walter Guyton Cady in 1921. George Washington Pierce designed and patented quartz crystal oscillators in 1923. Warren Marrison created the first quartz oscillator clock based on the work of Cady and Pierce in 1927.
Efforts to synthesize quartz began in the mid nineteenth 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 cooker. However, the quality and size of the crystals that were produced by these early efforts were poor.
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 the 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. cm) in diameter, the largest to date. 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.After the war, many laboratories attempted to grow large quartz crystals. In the United States, the U.S. Army Signal Corps contracted with Bell Laboratories 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
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.
Amethyst is a violet variety of quartz. The name comes from the Koine Greek ἀμέθυστος (Amethustos) where ἀ-(A) means "not" and μεθύσκω (methustos) means "intoxicate". It was a reference to the belief that the Amethyst stone protects the wearer from drunkenness. The ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.
Agate is a rock consisting primarily of cryptocrystalline silica, chiefly chalcedony, alternating with microgranular quartz. It is characterized by its fineness of grain and variety of color. Although agates may be found in various kinds of host rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.
Beryl ( BERR-əl) is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red (the rarest), and white. Beryl is also an ore source of beryllium.
A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks and occasionally organic materials that are not minerals are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.
A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. Minerals are most commonly associated with rocks due to the presence of minerals within rocks. These rocks may consist of one type of mineral, or may be an aggregate of two or more different types of minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic or are organic compounds in the sense of chemistry. Moreover, living beings often synthesize inorganic minerals that also occur in rocks.
Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.
A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency. This frequency is often used to keep track of time, as in quartz wristwatches, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits incorporating them became known as crystal oscillators, but other piezoelectric materials including polycrystalline ceramics are used in similar circuits.
Cryptocrystalline is a rock texture made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically in thin section by transmitted polarized light. Among the sedimentary rocks, chert and flint are cryptocrystalline. Carbonado, a form of diamond, is also cryptocrystalline. Volcanic rocks, especially of the acidic type such as felsites and rhyolites, may have a cryptocrystalline groundmass as distinguished from pure obsidian (acidic) or tachylyte (basic), which are natural rock glasses. Onyx is also a cryptocrystalline. Agates such as the fairburn agate are also composed of cryptocrystalline silica.
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2, most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant families of materials, existing as a compound of several minerals and as synthetic product. Notable examples include fused quartz, fumed silica, silica gel, and aerogels. It is used in structural materials, microelectronics (as an electrical insulator), and as components in the food and pharmaceutical industries.
Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Chalcedony's standard chemical structure (based on the chemical structure of quartz) is SiO2 (silicon dioxide).
The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words χρυσός chrysos and βήρυλλος beryllos, meaning "a gold-white spar". Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones, although they both contain beryllium. Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the Mohs scale of mineral hardness, between corundum (9) and topaz (8).
Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Opal is the national gemstone of Australia.
Smoky quartz is a grey, translucent variety of quartz that ranges in clarity from almost complete transparency to an almost-opaque brownish-gray or black crystal. Like other quartz gems, it is a silicon dioxide crystal. The smoky colour results from free silicon formed from the silicon dioxide by natural irradiation.
Cristobalite is a mineral polymorph of silica that is formed at very high-temperatures. It is used in dentistry as a component of alginate impression materials as well as for making models of teeth
Tridymite is a high-temperature polymorph of silica and usually occurs as minute tabular white or colorless pseudo-hexagonal crystals, or scales, in cavities in felsic volcanic rocks. Its chemical formula is SiO2. Tridymite was first described in 1868 and the type location is in Hidalgo, Mexico. The name is from the Greek tridymos for triplet as tridymite commonly occurs as twinned crystal trillings (compound crystals comprising three twinned crystal components).
Chrysoprase, chrysophrase or chrysoprasus is a gemstone variety of chalcedony that contains small quantities of nickel. Its color is normally apple-green, but varies to deep green. The darker varieties of chrysoprase are also referred to as prase.
Ametrine, also known as trystine or by its trade name as bolivianite, is a naturally occurring variety of quartz. It is a mixture of amethyst and citrine with zones of purple and yellow or orange. Almost all commercially available ametrine is mined in Bolivia.
Prasiolite is a green variety of quartz, a silicate mineral chemically silicon dioxide.
Moganite is an oxide mineral with the chemical formula SiO2 (silicon dioxide) that was discovered in 1984. It crystallises in the monoclinic crystal system. Moganite is considered a polymorph of quartz: it has the same chemical composition as quartz, but a different crystal structure.
Apart from Prague and Florence, the main Renaissance centre for crystal cutting was Milan.
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