View source for Quartz

{{About|the mineral|the quartz-based component in a crystal oscillator|Crystal oscillator|other uses|Quartz (disambiguation)}}
{{Infobox mineral
| name = '''Quartz'''
| category = Silicate mineral
| boxwidth = 24
| boxbgcolor =
| image = Quartz, Tibet.jpg
| caption = Quartz crystal cluster from [[Tibet]]
| formula = Silica ([[silicon dioxide]], SiO<sub>2</sub>)
| molweight =
| strunz = 04.DA.05
| dana = 75.01.03.01
| symmetry  = Trigonal [[H–M Symbol]] 32
| unit cell = a = 4.9133 [[Ångstrom|Å]], c = 5.4053 Å; Z = 3
| color = From colorless to black, through various colors 
| habit = 6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive
| system = α-quartz: [[trigonal]] trapezohedral class 3 2; β-quartz: [[Hexagonal crystal system|hexagonal]] 622<ref name=Deer>Deer, W. A., R. A. Howie and J. Zussman, ''An Introduction to the Rock Forming Minerals'', Logman, 1966, pp. 340–355 ISBN 0-582-44210-9</ref>
| lattice = [[hexagonal lattice system|hexagonal]]
| twinning = Common Dauphine law, Brazil law and Japan law
| cleavage = {0110} Indistinct
| fracture = Conchoidal
| tenacity = Brittle
| mohs = 7 – lower in impure varieties (defining mineral)
| luster = Vitreous – waxy to dull when massive
| refractive = n<sub>ω</sub> = 1.543–1.545 <br/>n<sub>ε</sub> = 1.552–1.554
| opticalprop = Uniaxial (+)
| birefringence = +0.009 (B-G interval)
| pleochroism = None
| streak = White
| gravity = 2.65; variable 2.59–2.63 in impure varieties
| density =
| melt = 1670 °C (β [[tridymite]]) <br>1717 °C (β [[cristobalite]])<ref name=Deer/>
| fusibility =
| diagnostic =
| solubility = Insoluble at [[Standard conditions for temperature and pressure|STP]]; 1&nbsp;ppm<sub>mass</sub> at 400&nbsp;°C and 34 [[bar (unit)|bar]] to 2600&nbsp;ppm<sub>mass</sub> at 500&nbsp;°C and 103 bar<ref name=Deer/>
| diaphaneity = Transparent to nearly opaque
| other = [[Piezoelectric]], may be [[triboluminescent]], chiral (hence optically active if not racemic)
| references = <ref name=Handbook>{{cite book|editor=Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. and Nichols, Monte C.  |title= Handbook of Mineralogy|publisher= Mineralogical Society of America|place= Chantilly, VA, US|url=http://rruff.geo.arizona.edu/doclib/hom/quartz.pdf|format=PDF|chapter=Quartz |accessdate=December 5, 2011|isbn=0962209716 |volume=II (Silica, Silicates)|year=1995}}</ref><ref name=Mindat>[http://www.mindat.org/min-3337.html Quartz]. Mindat.org</ref><ref name=Webmin>[http://www.webmineral.com/data/Quartz.shtml Quartz]. Webmineral. com</ref><ref name=Klein>{{cite book|author=Hurlbut, Cornelius S.; Klein, Cornelis|year=1985|title=Manual of Mineralogy|edition=20|isbn=0-471-80580-7}}</ref>
}}

'''Quartz''' is an abundant [[mineral]] in the [[Earth]]'s [[continental crust]]. It is made up of a continuous framework of SiO<sub>4</sub> [[silicon]]–[[oxygen]] [[tetrahedra]], with each oxygen being shared between two tetrahedra, giving an overall formula [[Silicon dioxide|SiO<sub>2</sub>]]. There are many different varieties of quartz, several of which are semi-precious [[gemstone]]s. Throughout the world, varieties of quartz have been, since antiquity, the most commonly used minerals in the making of [[jewelry]] and [[hardstone carving]]s.

==Crystal habit and structure==

Quartz belongs to the [[trigonal crystal system]]. The [[crystal habit|ideal crystal shape]] is a six-sided [[prism (geometry)|prism]] terminating with six-sided [[pyramid]]s at each end. In nature quartz crystals are often [[Crystal twinning|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. There are exceptions as ''doubly terminated'' crystals do occur. An occurrence in [[Herkimer County, New York]] is noted for these ''[[Herkimer diamond]]s'' with terminations at both ends. 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 and β-quartz===
[[File:a-quartz.png|thumb|left|100px|Crystal structure of α-quartz]]
[[File:b-quartz.png|thumb|left|100px|β-quartz]]

α-quartz crystallizes in the trigonal crystal system, space group ''P''3<sub>1</sub>21 or ''P''3<sub>2</sub>21. β-quartz belongs to the hexagonal system, space group ''P''6<sub>2</sub>22 or ''P''6<sub>4</sub>22.<ref>Crystal Data, Determinative Tables, ACA Monograph No. 5, American Crystallographic Association, 1963</ref> 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 (SiO<sub>4</sub> 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]].

==Occurrence==
Quartz is an essential constituent of [[granite]] and other [[felsic]] [[igneous rock]]s. It is very common in [[sedimentary rock]]s such as [[sandstone]] and [[shale]] and is also present in variable amounts as an accessory mineral in most [[carbonate rock]]s. It is also a common constituent of [[schist]], [[gneiss]], [[quartzite]] and other [[metamorphic rock]]s. Because of its resistance to [[weathering]] it is very common in stream sediments and in residual [[soil]]s.  Quartz, therefore, occupies the lowest potential to weather in the [[Goldich dissolution series]].

Quartz occurs in [[hydrothermal]] [[Vein (geology)|veins]] as [[gangue]] along with [[ore]] minerals. Large crystals of quartz are found in [[pegmatite]]s. Well-formed crystals may reach several meters in length and [[mass|weigh]] as much as {{convert|1400|lbs|kg}}.<ref>Deere, Howie and Zussman, ''Rock Forming Minerals: Framework Silicates,'' vol. 4, Wylie, 1964,  p.213</ref>

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]].<ref>{{cite news|url=http://news.bbc.co.uk/2/hi/technology/8178580.stm |last=Nelson |first=Sue |author-link=Sue Nelson |title=Silicon Valley's secret recipe|publisher=BBC News|date=2 August 2009}}</ref>

===Related silica minerals===
[[Tridymite]] and [[cristobalite]] are high-temperature [[Polymorphism (materials science)|polymorph]]s of SiO<sub>2</sub> 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]] and [[Seifertite]] are yet denser and higher-pressure polymorphs of quartz found in some meteorite impact sites. [[Lechatelierite]] is an [[amorphous]] silica [[glass]] SiO<sub>2</sub> which is formed by [[lightning]] strikes in quartz [[sand]].

===Synthetic quartz===
Most quartz used in microelectronics is produced synthetically. Large, flawless and untwinned crystals are produced in an [[autoclave]] via the [[Hydrothermal synthesis|hydrothermal process]].  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]] 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]], a measure of its piezoelectric response and an indicator of the purity of the crystal.<ref name=Ullmann/>
[[File:Synthetic quartz crystal.jpg|thumb|A synthetic silicon dioxide crystal grown by the [[Hydrothermal synthesis|hydrothermal method]], about 19&nbsp;cm long and weighing about 127 grams]]
High-temperature glass composed of silicon dioxide with no (or only small amounts of) other components is referred to as "quartz glass" or [[fused quartz]], although it is amorphous in structure, rather than crystalline.

==Uses==
Quartz is the source of many silicon compounds such as silicones (e.g. high performance [[polymer]]s), silicon (e.g. [[microelectronics]]), and many other compounds of commercial importance.  Quartz in the form of sand is reduced by [[carbothermic reaction]] as a first step in these energy-intensive processes.

Owing to its high thermal and chemical stability and abundance, quartz is widely used in many large-scale applications related to [[abrasive]]s, [[foundry]] materials, [[ceramics]], and [[cement]]s.<ref name=Ullmann>Otto W. Flörke et al. Silica" in Ullmann's Encyclopedia of Industrial Chemistry,, 2008, Wiley-VCH, Weinheim. {{DOI|10.1002/14356007.a23_583.pub3}}</ref>

===Piezoelectricity===
Quartz crystals have [[piezoelectricity|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. A common piezoelectric use 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 monitor]]s. Quartz's [[piezoelectric]] properties were discovered by [[Jacques Curie|Jacques]] and [[Pierre Curie]] in 1880. The [[quartz oscillator]] or resonator was first developed by [[Walter Guyton Cady]] in 1921.<ref>{{cite web|url=http://invention.smithsonian.org/centerpieces/quartz/inventors/cady.html|title=The Quartz Watch – Walter Guyton Cady|work=The Lemelson Center, National Museum of American History|publisher=[[Smithsonian Institution]]}}</ref> [[G. W. Pierce|George Washington Pierce]] designed and patented quartz crystal oscillators in 1923.<ref>{{cite web|url=http://invention.smithsonian.org/centerpieces/quartz/inventors/pierce.html|title=The Quartz Watch – George Washington Pierce|work=The Lemelson Center, National Museum of American History|publisher=[[Smithsonian Institution]]}}</ref> Warren Marrison created the first quartz oscillator clock based on the work of Cady and Pierce in 1927.<ref>{{cite web|url=http://invention.smithsonian.org/centerpieces/quartz/inventors/clock.html|title=The Quartz Watch – Warren Marrison|work=The Lemelson Center, National Museum of American History|publisher=[[Smithsonian Institution]]}}</ref>

===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]] or [[cryptocrystalline]] 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 materials|transparent]] or [[translucent]].  Common colored varieties include citrine, rose quartz, [[amethyst]], smoky quartz and milky quartz. 

=====Citrine=====
[[File:Citrin cut.jpg|thumb|150px|Citrine]]
{{Redirect|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]]. Citrine contains traces of Fe<sup>3+</sup> and is rarely found naturally. The name is derived from [[Latin]] citrina which means "yellow".<ref>[http://www.mindat.org/min-1054.html Citrine]. Mindat.org</ref>

=====Rose quartz=====
[[File:Quartz-51109.jpg|thumb|150px|Rose quartz crystals, Minas Gerais]]
''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 massive material. Some types of quartz contain microscopic [[rutile]] needles which produces an [[asterism (gemmology)|asterism]] in transmitted light. Recent [[X-ray diffraction]] studies suggest that the color is due to thin microscopic fibers of possibly [[dumortierite]] within the massive quartz.<ref>[http://www.mindat.org/show.php?id=3456 Rose Quartz]. Mindat.org</ref>

In crystal form (rarely found) it is called ''pink quartz'' and its color 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|Rumford]], [[Maine]], US, but most crystals on the market come from [[Minas Gerais]], [[Brazil]].<ref>[http://minerals.caltech.edu/ge114/Lecture_Topics/Quartz/Index.htm Colored Varieties of Quartz], Caltech</ref>

=====Amethyst=====

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

=====Smoky quartz=====

[[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.

=====Milky quartz=====
[[File:QuartzUSGOV.jpg|thumb|150px|Milky quartz sample]]
''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]] 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.<ref>[http://www.galleries.com/minerals/silicate/milky_qu/milky_qu.htm Milky quartz, the cloudy white variety of quartz]. galleries.com</ref>

====Microcrystalline varieties====
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]].<ref name="heany_1994">{{cite journal|last=Heaney |first=Peter J. |year=1994 |title=Structure and Chemistry of the low-pressure silica polymorphs |journal=Reviews in Mineralogy and Geochemistry |volume=29 |pages=1–40|url=http://rimg.geoscienceworld.org/cgi/content/abstract/29/1/1|issue=1}}</ref> Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are [[agate]], [[onyx]], [[carnelian]], and [[jasper]].

====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.

{| class="wikitable"
|+ Macrocrystalline varieties
| Rock crystal || Clear, colorless
|-
| [[Amethyst]] || Purple, transparent
|-
| Citrine || Yellow to reddish orange to brown, greenish yellow
|-
| [[Prasiolite]] || Mint green, transparent
|-
| Rose quartz || Pink, translucent
|-
| Rutilated quartz || Contains [[Acicular (crystal habit)|acicular]] (needles) [[Inclusion (mineral)|inclusion]]s of [[rutile]]
|-
| Milk quartz || White, translucent to opaque
|-
|[[Smoky quartz]] || Brown to gray, opaque
|}

{| class="wikitable"
|+ Microcrystalline varieties
| [[Chalcedony]] || Cryptocrystalline quartz and moganite mixture. The term is generally only used for white or lightly colored material. Otherwise more specific names are used.
|-
| [[Agate]] || Multi-colored, banded chalcedony, semi-translucent to translucent
|-
| [[Onyx]] || Agate where the bands are straight, parallel and consistent in size.
|-
| [[Jasper]] || Opaque cryptocrystalline quartz, typically red to brown
|-
| [[Aventurine]] || Translucent chalcedony with small inclusions (usually mica) that shimmer.
|-
| [[Tiger's Eye]] || Fibrous gold to red-brown colored quartz, exhibiting [[chatoyancy]].
|-
| [[Carnelian]] || 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]] is widely heat-treated to deepen its color.

==History of naming and usage==

[[File:Transparency.jpg|right|thumb|Quartz crystal showing [[transparent materials|transparency]]]]
The word "quartz" is derived from the [[German language|German]] word "quarz" and its [[Middle High German]] ancestor "twarc", which probably originated in [[Slavic languages|Slavic]] (cf. Czech tvrdý ("hard"), Polish twardy ("hard")).<ref>{{OEtymD|quartz}}</ref>{{Audio|De-Quarz.ogg|''Quarz''}},<ref>[http://german.about.com/library/blvoc_gerloan.htm German Loan Words in English]. german.about.com</ref> which is of Slavic origin (Czech miners called it ''křemen''). Other sources attribute the word's origin to the [[Upper Saxon German|Saxon]] word ''Querkluftertz'', meaning ''cross-vein ore''.<ref>[http://www.mineralatlas.com/mineral%20general%20descriptions/Q/quartzpcd.htm ''Mineral Atlas''], Queensland University of Technology</ref>

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 the [[Republic of Ireland]]. The [[Irish language|Irish]] word for quartz is ''grian cloch'', which means 'stone of the sun'. Quartz was also used in [[Prehistoric Ireland]], as well as many other countries, for [[stone tool]]s; both vein quartz and rock crystal were [[knapping|knapped]] as part of the [[lithic technology]] of the prehistoric peoples.<ref>Driscoll, Killian. 2010. [http://www.scribd.com/doc/34574206/Driscoll-K-2010-Understanding-quartz-technology-in-early-prehistoric-Ireland-Volumes-1-and-2-PhD-thesis-UCD-School-of-Archaeology-University-Col Understanding quartz technology in early prehistoric Ireland]. PhD thesis, UCD School of Archaeology, University College Dublin</ref>

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. He also knew of the ability of quartz to split light into a [[spectrum]]. This idea persisted until at least the 17th century.

In the 17th century, [[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° angle.

[[Charles B. Sawyer]] invented the commercial quartz crystal manufacturing process in [[Cleveland]], [[Ohio]], [[United States]]. This initiated the transition from mined and cut quartz for electrical appliances to manufactured quartz.

==See also==
{{Wikisource|1911 Encyclopædia Britannica/Quartz}}
*[[Fused quartz]]
*[[List of minerals]]
*[[Shocked quartz]]
*[[Quartz reef mining]]
*[[Flint]]

==References==
{{Reflist|35em}}

==External links==
{{Commons|Quartz}}
*[http://www.quartzpage.de/ Quartz varieties, properties, crystal morphology. Photos and illustrations]
*[http://rockhoundingar.com/quartz.php ''Arkansas quartz'', Rockhounding Arkansas]
*Gilbert Hart, "[http://www.minsocam.org/MSA/collectors_corner/arc/silicanom.htm Nomenclature of Silica]," ''American Mineralogist'', Volume 12, pages 383–395, 1927
*[http://labs.sci.qut.edu.au/minerals/mineral%20general%20descriptions/Q/quartzpcd.htm Queensland University of Technology] Origin of the word quartz.
*Charles Sawyer's [https://goby.nrl.nav.mil/branch/UFFC_Archive/cd01/fc/proceed/1959/proceed/s5910462.pdf cultured quartz process description] (inventor of the commercial quartz crystal manufacturing process) (pdf) 
*{{Cite web|url=http://invention.smithsonian.org/centerpieces/quartz/inventors/index.html|title=The Quartz Watch – Inventors|work=The Lemelson Center, National Museum of American History|publisher=[[Smithsonian Institution]]}}
*[http://www.connogue.com/quartslab/html/terminology.html Terminology used to describe the characteristics of Quartz Crystals when used as oscillators]
*[http://www.iom-world.org/pubs/IOM_TM9503.pdf A follow-up study of miners exposed to unusual concentrations of quartz] by BG Miller and others. [[Institute of Occupational Medicine]] Research Report TM/95/03
*[http://www.iom-world.org/pubs/IOM_TM9105.pdf Further studies on the importance of quartz in the development of coalworkers’ pneumoconiosis] by JMG Davis and others. [[Institute of Occupational Medicine]] Research Report TM/91/05

{{Jewellery}}
{{Silica minerals}}
{{Use dmy dates|date=December 2010}}

[[Category:Quartz varieties]]
[[Category:Piezoelectric materials]]
[[Category:Dielectrics]]
[[Category:German loanwords]]
[[Category:Symbols of Georgia (U.S. state)]]
[[Category:Trigonal minerals]]

{{Link GA|de}}

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