Quartz

Quartz

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Quartz is the second-most-abundant mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 in the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...

, after feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....

. It is made up of a continuous framework of SiO4 silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

. There are many different varieties of quartz, several of which are semi-precious gemstone
Gemstone
A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...

s. Especially in Europe and the Middle East, varieties of quartz have been since antiquity the most commonly used minerals in the making of jewelry and hardstone carving
Hardstone carving
Hardstone carving is a general term in art history and archaeology for the carving for artistic purposes of semi-precious stones, also known as gemstones, such as jade, rock crystal , agate, onyx, jasper, serpentine or carnelian, and for an object made in this way. Normally the objects are small,...

s.

Crystal habit and structure


Quartz belongs to the trigonal crystal system
Crystal system
In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals...

. The ideal crystal shape
Crystal habit
Crystal habit is an overall description of the visible external shape of a mineral. This description can apply to an individual crystal or an assembly of crystals or aggregates....

 is a six-sided prism
Prism (geometry)
In geometry, a prism is a polyhedron with an n-sided polygonal base, a translated copy , and n other faces joining corresponding sides of the two bases. All cross-sections parallel to the base faces are the same. Prisms are named for their base, so a prism with a pentagonal base is called a...

 terminating with six-sided pyramid
Pyramid
A pyramid is a structure whose outer surfaces are triangular and converge at a single point. The base of a pyramid can be trilateral, quadrilateral, or any polygon shape, meaning that a pyramid has at least three triangular surfaces...

s at each end. In nature quartz crystals are often twinned
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two 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, but because the crystals must be attached at the other end to a matrix, only one termination pyramid is present. There are exceptions as doubly terminated crystals do occur. An occurrence in Herkimer County, New York
Herkimer County, New York
Herkimer County is a county located in the U.S. state of New York. It was created in 1791 north of the Mohawk River out of part of Montgomery County. As of the 2010 census, the population was 64,519. It is named after General Nicholas Herkimer, who died from battle wounds in 1777 after taking part...

 is noted for these Herkimer diamond
Herkimer diamond
Herkimer diamond is a generic name for a double-terminated quartz crystal discovered within exposed outcrops of dolostone in and around Herkimer County, New York and the Mohawk River Valley...

s
with terminations at both ends. A quartz geode
Geode
Geodes are geological secondary sedimentary structures which occur in sedimentary and certain volcanic rocks. Geodes are essentially spherical masses of mineral matter that were deposited sygenetically within the rock formations they are found in. Geodes have a Chalcedony shell containing...

 is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward.

α-quartz and β-quartz


α-quartz crystallizes in the trigonal crystal system, space group P3121 or P3221. β-quartz belongs to the hexagonal system, space group P6221 or P6421. 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, this process is called the quartz inversion
Quartz inversion
The room-temperature form of quartz, α-quartz, undergoes a reversible change in crystal structure at 573 °C to form β-quartz. This phenomenon is called an inversion, and for the α to β quartz inversion is accompanied by a linear expansion of 0.45 %. This inversion can lead to cracking of...

.

Occurrence


Quartz is an essential constituent of granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

 and other felsic
Felsic
The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....

 igneous rock
Igneous rock
Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...

s. It is very common in sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

s such as sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

 and shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

 and is also present in variable amounts as an accessory mineral in most carbonate rock
Carbonate rock
Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite .Calcite can be either dissolved by groundwater or precipitated by...

s. It is also a common constituent of schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...

, gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...

, quartzite
Quartzite
Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...

 and other metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

s. Because of its resistance to weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...

 it is very common in stream sediments and in residual soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

s. Quartz, therefore, occupies the lowest potential to weather in the Goldich dissolution series
Goldich dissolution series
The Goldich dissolution series is a way of predicting the relative stability or weathering rate of various minerals on the Earth's surface. S. S. Goldich came up with the series in 1938 after studying soil profiles...

.

Quartz occurs in hydrothermal veins
Vein (geology)
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation...

 as gangue
Gangue
In mining, gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. The separation of mineral from gangue is known as mineral processing, mineral dressing or ore dressing and it is a necessary and often significant aspect of mining...

 along with ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

 minerals. Large crystals of quartz are found in pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....

s. Well-formed crystals may reach several meters in length and weigh
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 as much as 1400 lbs.

Naturally occurring quartz crystals of extremely high purity, necessary for the crucibles and other equipment used for growing silicon wafers in the semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 industry, are expensive and rare. A major mining location for high purity quartz is the Spruce Pine Gem Mine in Spruce Pine, North Carolina
Spruce Pine, North Carolina
Spruce Pine is a town in Mitchell County, North Carolina, United States. The population was 2,175 at the 2010 census.-History:Spruce Pine was founded in 1907 when the Clinchfield Railroad made its way up the North Toe River from Erwin, Tennessee...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

.

Related silica minerals


Tridymite
Tridymite
Tridymite is a high-temperature polymorph of quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal triclinic crystals, or scales, in cavities in acidic volcanic rocks. Its chemical formula is SiO2. Tridymite was first described in 1868 and the type location is in Hidalgo,...

 and cristobalite
Cristobalite
The mineral cristobalite is a high-temperature polymorph of silica, meaning that it has the same chemical formula, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group which also include coesite, tridymite and stishovite...

 are high-temperature polymorph
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

s of SiO2 that occur in high-silica volcanic rocks. Coesite
Coesite
Coesite[p] is a form of silicon dioxide SiO2 that is formed when very high pressure , and moderately high temperature , are applied to quartz. Coesite was first synthesized by Loring Coes, Jr., a chemist at the Norton Company, in 1953. In 1960, coesite was found by Edward C. T...

 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
Stishovite
Stishovite is an extremely hard, dense tetragonal form of silicon dioxide. It was long considered the hardest known oxide; however, boron suboxide has recently been discovered to be much harder...

 and Seifertite
Seifertite
Seifertite is a silicate mineral with the formula SiO2 and is one of the densest polymorphs of quartz. It has only been found in Martian and lunar meteorites where it is presumably formed from either tridymite or cristobalite – other polymorphs of quartz – as a result of heating during the...

 are yet denser and higher-pressure polymorphs of quartz found in some meteorite impact sites. Lechatelierite
Lechatelierite
Lechatelierite is silica glass, amorphous SiO2. One common way in which lechatelierite forms naturally is by very high temperature melting of quartz sand during a lightning strike...

 is an amorphous silica glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 SiO2 which is formed by lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

 strikes in quartz sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

.

Synthetic quartz


Most quartz used in microelectronics is produced synthetically. Large, flawless and untwinned crystals are produced in an autoclave
Autoclave
An autoclave is an instrument used to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents. It was invented by Charles Chamberland in 1879, although a precursor known as the...

 via the hydrothermal process
Hydrothermal synthesis
Hydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high vapor pressures; also termed "hydrothermal method". The term "hydrothermal" is of geologic origin. Geochemists and mineralogists have studied hydrothermal phase...

. The process involves treating crushed natural quartz with hot aqueous solution of a base such as sodium hydroxide. The hydroxide serves as a "mineralizer", i.e. it helps dissolve the "nutrient" quartz. High temperatures are required, often around 675 °C. The dissolved quartz then recrystallizes at a seed crystal
Seed crystal
A seed crystal is a small piece of single crystal/polycrystal material from which a large crystal of the same material typically is to be grown...

 at slightly lower temperatures. Approximately 200 tons of quartz were produced in the US in 2005; large synthesis facilities exist throughout the world. Synthetic quartz is often evaluated on the basis of its Q factor
Q factor
In physics and engineering the quality factor or Q factor is a dimensionless parameter that describes how under-damped an oscillator or resonator is, or equivalently, characterizes a resonator's bandwidth relative to its center frequency....

, a measure of its piezoelectric response and an indicator of the purity of the crystal.

Uses


Quartz is the source of many silicon compounds such as silicones (e.g. high performance polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

s), silicon (e.g. microelectronics
Microelectronics
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture of very small electronic components. Usually, but not always, this means micrometre-scale or smaller,. These devices are made from semiconductors...

), and many other compounds of commercial importance. Quartz in the form of sand is reduced by carbothermic reaction
Carbothermic reaction
Carbothermic reactions use carbon as reducing agent, usually for metal oxides. These chemical reactions are usually conducted at several hundreds of degree Celsius. Such processes are applied for production of the elemental forms of many elements. Carbothermic reactions are not however useful for...

 as a first step in these energy-intensive processes.

Owing to its high thermal and chemical stability and abundance, quartz is widely used many large-scale applications related to abrasive
Abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away...

s, foundry
Foundry
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...

 materials, ceramics, and cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

s.

Piezoelectricity


Quartz crystals have piezoelectric
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...

 properties: they develop an electric potential upon the application of mechanical stress. An early use of this property of quartz crystals was in phonograph
Phonograph
The phonograph record player, or gramophone is a device introduced in 1877 that has had continued common use for reproducing sound recordings, although when first developed, the phonograph was used to both record and reproduce sounds...

 pickups. A common piezoelectric use of quartz today is as a crystal oscillator
Crystal oscillator
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 very precise frequency...

. The quartz clock
Quartz clock
A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks...

 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
Quartz crystal microbalance
A quartz crystal microbalance measures a mass per unit area by measuring the change in frequency of a quartz crystal resonator. The resonance is disturbed by the addition or removal of a small mass due to oxide growth/decay or film deposition at the surface of the acoustic resonator...

 and in thin-film thickness monitor
Thin-film thickness monitor
Thin-film thickness monitors, deposition rate controllers, and so on, are a family of instruments used in high and ultra-high vacuum systems. They can measure the thickness of a thin film, not only after it has been made, but while it is still being deposited, and some can control either the final...

s.Quartz's piezoelectric properties were discovered by Jacques
Jacques Curie
Paul-Jacques Curie was a French physicist and professor at the University of Montpellier. He and his brother, Pierre Curie, studied pyroelectricity in the 1880s, leading to their discovery of some of the mechanisms behind piezoelectricity....

 and Pierre Curie
Pierre Curie
Pierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. He was the son of Dr. Eugène Curie and Sophie-Claire Depouilly Curie ...

 in 1880. The quartz oscillator or resonator was first developed by Walter Guyton Cady
Walter Guyton Cady
Dr. Walter Guyton Cady was a noted American physicist and electrical engineer. He was a pioneer in piezoelectricity, and in 1921 developed the first crystal oscillator....

 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.

Gemstone and lapidary varieties


The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline
Microcrystalline
A microcrystalline material is a crystallized substance or rock that contains small crystals visible only through microscopic examination.-See also:* Macrocrystalline* Microcrystalline silicon* Protocrystalline* Rock microstructure...

 or cryptocrystalline
Cryptocrystalline
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...

 varieties (aggregates of crystals visible only under high magnification).

Coarsely crystalline varieties


Pure quartz, traditionally called rock crystal (sometimes called clear quartz), is colorless and transparent or translucent. Common colored varieties include citrine, rose quartz, amethyst
Amethyst
Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek ἀ a- and μέθυστος methustos , a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief...

, smoky quartz and milky quartz.
Citrine



Citrine is a variety of quartz whose color ranges from a pale yellow to brown. Natural citrines are rare; most commercial citrines are heat-treated amethyst
Amethyst
Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek ἀ a- and μέθυστος methustos , a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief...

. Citrine contains traces of Fe3+ and is rarely found naturally. The name is derived from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 citrina which means "yellow".
Rose quartz


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
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, or manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

, in the massive material. Some types of quartz contain microscopic rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...

 needles which produces an asterism
Asterism (gemmology)
Asteria, or star stone is a name applied to ornamental stones that exhibit a luminous star when cut en cabochon. The typical asteria is the star-sapphire, generally a bluish-grey corundum, milky or opalescent, with a star of six rays...

 in transmitted light. Recent X-ray diffraction studies suggest that the color is due to thin microscopic fibers of possibly dumortierite
Dumortierite
Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, Al7BO33O3. Dumortierite crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet...

 within the massive quartz.

In crystal form (rarely found) it is called pink quartz and its color is thought to be caused by trace amounts of phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

 or aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

. The color in crystals is apparently photosensitive and subject to fading. The first crystals were found in a pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....

 found near Rumford, Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

, USA, but most crystals on the market come from Minas Gerais
Minas Gerais
Minas Gerais is one of the 26 states of Brazil, of which it is the second most populous, the third richest, and the fourth largest in area. Minas Gerais is the Brazilian state with the largest number of Presidents of Brazil, the current one, Dilma Rousseff, being one of them. The capital is the...

, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

.
Amethyst

Amethyst
Amethyst
Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek ἀ a- and μέθυστος methustos , a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief...

 is a form of quartz that ranges from a bright to dark or dull purple color.
Smoky quartz

Smoky quartz
Smoky quartz
Smoky or smokey quartz is a brown to black variety of quartz. 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.-Morion:...

 is a gray, translucent version of quartz. It ranges in clarity from almost complete transparency to a brownish-gray crystal that is almost opaque.
Milky quartz


Milky quartz may be the most common variety of crystalline quartz and can be found almost anywhere. The white color may be caused by minute fluid inclusions
Fluid inclusions
thumb|250px|Trapped in a time capsule the same size as the diameter of a human hair, the ore-forming liquid in this inclusion was so hot and contained so much dissolved solids that when it cooled, crystals of halite, sylvite, gypsum, and hematite formed. As the samples cooled, the fluid shrank more...

 of gas, liquid, or both, trapped during the crystal formation. The cloudiness caused by the inclusions effectively bars its use in most optical and quality gemstone applications.

Microcrystalline varieties


The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony
Chalcedony
Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic...

 is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite
Moganite
Moganite is a silicate mineral with the chemical formula SiO2 that was discovered in 1984. It crystallises in the monoclinic crystal system...

. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate
Agate
Agate is a microcrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.-Etymology...

, onyx
Onyx
Onyx is a banded variety of chalcedony. The colors of its bands range from white to almost every color . Commonly, specimens of onyx contain bands of black and/or white.-Etymology:...

, carnelian
Carnelian
Carnelian is a brownish-red mineral which is commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker...

, and jasper
Jasper
Jasper, a form of chalcedony, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone. It can be highly polished and is used for vases, seals, and at one time for...

.

Varieties (according to microstructure)


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.
Macrocrystalline varieties
Rock crystal Clear, colorless
Amethyst
Amethyst
Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek ἀ a- and μέθυστος methustos , a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief...

 
Purple, transparent
Citrine Yellow to reddish orange to brown, greenish yellow
Prasiolite
Prasiolite
Prasiolite, green-quartz or vermarine is a green form of quartz, a silicate mineral chemically silicon dioxide. Prasiolite is one of several quartz varieties....

 
Mint green, transparent
Rose quartz Pink, translucent
Rutilated quartz Contains acicular
Acicular (crystal habit)
Acicular, in mineralogy, refers to a crystal habit composed of a radiating mass of slender, needle-like crystals. Minerals with this habit tend to be fragile and complete, undamaged specimens can be uncommon.-Examples:...

 (needles) inclusion
Inclusion (mineral)
In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation.In gemology, an inclusion is a characteristic enclosed within a gemstone, or reaching its surface from the interior....

s of rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...

Milk quartz White, translucent to opaque
Smoky quartz
Smoky quartz
Smoky or smokey quartz is a brown to black variety of quartz. 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.-Morion:...

 
Brown to gray, opaque

Microcrystalline varieties
Chalcedony
Chalcedony
Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic...

 
Cryptocrystalline quartz and moganite mixture. The term is generally only used for white or lightly colored material. Otherwise more specific names are used.
Agate
Agate
Agate is a microcrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.-Etymology...

 
Multi-colored, banded chalcedony, semi-translucent to translucent
Onyx
Onyx
Onyx is a banded variety of chalcedony. The colors of its bands range from white to almost every color . Commonly, specimens of onyx contain bands of black and/or white.-Etymology:...

 
Agate where the bands are straight, parallel and consistent in size.
Jasper
Jasper
Jasper, a form of chalcedony, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone. It can be highly polished and is used for vases, seals, and at one time for...

 
Opaque cryptocrystalline quartz, typically red to brown
Aventurine
Aventurine
Aventurine is a form of quartz, characterised by its translucency and the presence of platy mineral inclusions that give a shimmering or glistening effect termed aventurescence....

 
Translucent chalcedony with small inclusions (usually mica) that shimmer.
Tiger's Eye
Tiger's eye
Tiger's eye is a chatoyant gemstone that is usually a metamorphic rock that is a golden to red-brown color, with a silky luster. A member of the quartz group, it is a classic example of pseudomorphous replacement by silica of fibrous crocidolite...

 
Fibrous gold to red-brown colored quartz, exhibiting chatoyancy
Chatoyancy
In gemology, chatoyancy , or chatoyance, is an optical reflectance effect seen in certain gemstones. Coined from the French "œil de chat," meaning "cat's eye," chatoyancy arises either from the fibrous structure of a material, as in tiger eye quartz, or from fibrous inclusions or cavities within...

.
Carnelian
Carnelian
Carnelian is a brownish-red mineral which is commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker...

 
Reddish orange chalcedony, translucent

Synthetic and artificial treatments


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
Carnelian
Carnelian is a brownish-red mineral which is commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker...

 is widely heat-treated to deepen its color.

History of naming and usage



The word "quartz" is derived from the German
German language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....

 word "quarz" and its Middle High German
Middle High German
Middle High German , abbreviated MHG , is the term used for the period in the history of the German language between 1050 and 1350. It is preceded by Old High German and followed by Early New High German...

 ancestor "twarc", which probably originated in Slavic
Slavic languages
The Slavic languages , a group of closely related languages of the Slavic peoples and a subgroup of Indo-European languages, have speakers in most of Eastern Europe, in much of the Balkans, in parts of Central Europe, and in the northern part of Asia.-Branches:Scholars traditionally divide Slavic...

 (cf. Czech tvrdý ("hard"), Polish twardy ("hard"))., which is of Slavic origin (Czech miners called it křemen). Other sources attribute the word's origin to the Saxon
Upper Saxon German
Upper Saxon is a Central German dialect spoken in much of the modern German states of Saxony and Thuringia. Contrary to its name it is not a descendant of Old Saxon. The degree of accent varies from place to place within the states, with it being anywhere from a relatively mild accent in the...

 word Querkluftertz, meaning cross-vein ore.

Quartz is the most common material identified as the mystical substance maban
Maban
Maban or Mabain is a material that is held to be magical in Australian Aboriginal mythology. It is the material from which the shamans and elders of indigenous Australia supposedly derive their magical powers.-References:...

 in Australian Aboriginal mythology
Australian Aboriginal mythology
Australian Aboriginal myths are the stories traditionally performed by Aboriginal peoples within each of the language groups across Australia....

. It is found regularly in passage tomb cemeteries in Europe in a burial context, such as Newgrange
Newgrange
Newgrange is a prehistoric monument located in County Meath, on the eastern side of Ireland, about one kilometre north of the River Boyne. It was built around 3200 BC , during the Neolithic period...

 or Carrowmore
Carrowmore
Carrowmore, County Sligo is one of the four major passage tomb cemeteries in Ireland. It is located at the centre of a prehistoric ritual landscape on the Cúil Irra Peninsula in County Sligo in Ireland....

 in the Republic of Ireland
Republic of Ireland
Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

. The Irish
Irish language
Irish , also known as Irish Gaelic, is a Goidelic language of the Indo-European language family, originating in Ireland and historically spoken by the Irish people. Irish is now spoken as a first language by a minority of Irish people, as well as being a second language of a larger proportion of...

 word for quartz is grian cloch, which means 'stone of the sun'. Quartz was also used in Prehistoric Ireland
Prehistoric Ireland
The prehistory of Ireland has been pieced together from archaeological and genetic evidence; it begins with the first evidence of Mesolithic hunter-gatherers settling in Ireland around 7000 BC and finishes with the start of the historical record, around AD 400. The prehistoric period covers the...

, as well as many other countries, for stone tool
Stone tool
A stone tool is, in the most general sense, any tool made either partially or entirely out of stone. Although stone tool-dependent societies and cultures still exist today, most stone tools are associated with prehistoric, particularly Stone Age cultures that have become extinct...

s; both vein quartz and rock crystal were knapped as part of the lithic technology
Lithic Technology
In archeology, lithic technology refers to a broad array of techniques and styles to produce usable tools from various types of stone. The earliest stone tools were recovered from modern Ethiopia and were dated to between two-million and three-million years old...

 of the prehistoric peoples.

Roman naturalist Pliny the Elder
Pliny the Elder
Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

 believed quartz to be water ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

, 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. He also knew of the ability of quartz to split light into a spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

. This idea persisted until at least the 17th century.

In the 17th century, Nicolas Steno
Nicolas Steno
Nicolas Steno |Latinized]] to Nicolaus Steno -gen. Nicolai Stenonis-, Italian Niccolo' Stenone) was a Danish pioneer in both anatomy and geology. Already in 1659 he decided not to accept anything simply written in a book, instead resolving to do research himself. He is considered the father of...

's study of quartz paved the way for modern crystallography
Crystallography
Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...

. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60° angle.

Charles B. Sawyer invented the commercial quartz crystal manufacturing process in Cleveland, Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. This initiated the transition from mined and cut quartz for electrical appliances to manufactured quartz.

See also


  • Fused quartz
    Fused quartz
    Fused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...

  • List of minerals
  • Shocked quartz
    Shocked quartz
    Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure , the crystalline structure of quartz will be deformed along planes inside the crystal...

  • Quartz reef mining
    Quartz reef mining
    Primary gold typically occurs in quartz veins. The extraction of gold ore from these hard quartz veins was historically referred to as quartz reef mining....


External links