Zircon
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2008-07-10T23:04:35Z
Melesse
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{{for|the spy satellite of this codename|Zircon (satellite)}}
{{otheruses4|the natural mineral Zircon|the chemically different synthetic diamond substitute|Cubic zirconia}}
{{Infobox mineral
| name = Zircon
| category =
| boxwidth =
| boxbgcolor =
| image = zircão.jpeg
| caption = Zircon crystal from Tocantins, [[Brazil]](unknown scale)
| formula = [[zirconium]] [[silicate]] ZrSiO<sub>4</sub>
| molweight =
| color = brown, red, yellow, green, black, and colorless
| habit = dipyramidal prismatic
| system = [[Tetragonal]]; 4/m 2/m 2/m
| twinning =
| cleavage = indistinct, two directions
| fracture = Subconchoidal to uneven—brittle
| mohs = 7.5
| luster = Adamantine
| refractive = nω=1.967–2.015</br>nε=1.920–1.960
| opticalprop =
| birefringence = δ=0.047–0.055
| pleochroism =
| streak = White
| gravity = 4.6–4.7
| melt =
| fusibility = Infusible
| diagnostic =
| solubility = Insoluble
| diaphaneity =
| other = [[Fluorescence|Fluorescent]] and [[radioactivity|radioactive]]
}}
'''Zircon''' is a [[mineral]] belonging to the group of [[Silicate minerals|nesosilicates]]. Its chemical name is [[zirconium silicate]] and its corresponding chemical formula is [[Zirconium|Zr]][[Silicon|Si]][[Oxygen|O]]<sub>4</sub>. [[Hafnium]] is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is [[tetragonal]] [[crystal class]]. The natural color of zircon varies between colorless, yellow-golden, red, brown, and green. Colorless specimens that show gem quality are a popular substitute for [[diamond]]; these specimens are also known as "Matura diamond". It is not to be confused with [[cubic zirconia]], a synthetic substance with a completely different chemical composition.
The name either derives from the [[Arabic language|Arabic]] word ''zarqun'', meaning [[vermilion]], or from the [[Persian language|Persian]] ''zargun'', meaning golden-colored. These words are corrupted into "[[jargoon]]", a term applied to light-colored zircons. Yellow zircon is called '''hyacinth''', from a word of East Indian origin; in the Middle Ages all yellow stones of East Indian origin were called hyacinth, but today this term is restricted to the yellow zircons.
Zircon is regarded as the traditional [[Birthstone#Birthstones|birthstone]] for December.
== Properties ==
[[Image:zircon microscope.jpg|left|150px|thumb|Optical microscope photograph; the length of the crystal is about 250 [[µm]].]]
Zircon is a remarkable mineral, if only for its almost ubiquitous presence in the [[Crust (geology)|crust]] of Earth. It is found in [[igneous rock]]s (as primary crystallization products), in [[metamorphic rock]]s and in [[sedimentary rock]]s (as detrital grains). Large zircon crystals are seldom abundant. Their average size, e.g. in [[granitoid|granite]] rocks, is about 100–300 µm, but they can also grow to sizes of several centimeters, especially in [[pegmatite]]s.
Owing to their [[uranium]] and [[thorium]] content, some zircons may undergo [[metamictization]]. This partially disrupts the crystal structure and explains the highly variable properties of zircon.
Zircon is a common accessory mineral and found worldwide. Noted occurrences include: in the [[Ural Mountains]]; Trentino, Monte Somma; and [[Vesuvius]], [[Italy]]; Arendal, [[Norway]]; [[Sri Lanka]], [[India]]; [[Thailand]]; [[Ratanakiri]], [[Cambodia]]; at the Kimberley mines, [[Republic of South Africa]]; [[Madagascar]]; and in [[Canada]] in Renfrew County, [[Ontario]], and [[Grenville, Quebec]]. In the [[United States]]: [[Litchfield, Maine]]; [[Chesterfield, Massachusetts]]; in Essex, Orange, and St. Lawrence Counties, [[New York]]; [[Henderson County, North Carolina]]; the [[Pikes Peak]] district of [[Colorado]]; and [[Llano County, Texas]].
[[Thorite]] (ThSiO<sub>4</sub>) is an isostructural related mineral.
Zircon can come in red, brown, yellow, hazel, black, or colorless. The color of zircons below gem quality can be changed by heat treatment. Depending on the amount of heat applied, colorless, blue, and golden-yellow zircons can be made.
== Uses ==
[[Image:ZirconUSGOV.jpg|thumb|Zircon dust]]
Zircons are commercially mined for the metal zirconium, and are used for abrasive and insulating purposes. It is the source of [[zirconium oxide]], one of the most [[refractory]] materials known. Crucibles of ZrO are used to fuse [[platinum]] at temperatures in excess of 1755 <sup>o</sup>C. Zirconium metal is used in [[nuclear reactors]] due to its [[neutron]] absorption properties. Large specimens are appreciated as [[gemstone]]s, owing to their high [[refractive index]] (zircon has a refractive index of around 1.95, [[diamond]] around 2.4).
== Occurrence ==
[[Image:Zirconium mineral concentrates - world production trend.svg|thumb|left|World production trend of zirconium mineral concentrates]]
Zircon is a common accessory to trace mineral constituent of most [[granite]] and felsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands. Zircon is rare within mafic rocks and very rare within ultramafic rocks aside from a group of ultrapotassic intrusive rocks such as [[kimberlite]]s, carbonatites and lamprophyre where zircon can occasionally be found as a trace mineral owing to the unusual magma genesis of these rocks.
Zircon forms economic concentrations within [[heavy mineral sands ore deposits]], within certain [[pegmatite]]s and within some rare alkaline volcanic rocks, for example the Toongi Trachyte, Dubbo, New South Wales Australia<ref>{{cite web | url=http://www.alkane.com.au/projects/nsw/dubbo/DZP%20Summary%20June07.pdf | title=Dubbo Zirconia Project Fact Sheet June 2007 | date= 06/2007 | first=Alkane Resources Limited | accessdate=2007-09-10}}</ref> in association with the zirconium-hafnium minerals [[eudiyalite]] and [[armstrongite]].
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== Zircons and radiometric dating ==
The pervasive occurrence of zircon has become more important since the discovery of [[radiometric dating]]. Zircons contain amounts of [[uranium]] and [[thorium]] (from 10 [[Parts per million|ppm]] up to 1 wt%) and can be dated using modern analytical techniques. Since zircons can survive geologic processes like [[erosion]], transport, even high-grade [[metamorphism]], they are used as [[protolith indicator]]s.
The [[oldest rock|oldest minerals]] found so far are zircons from [[Jack Hills]] in the [[Narryer Gneiss Terrane]], [[Yilgarn Craton]], [[Western Australia]], with an age of 4.404 billion years,<ref>http://www.geology.wisc.edu/%7Evalley/zircons/Wilde2001Nature.pdf</ref> interpreted to be the age of crystallization. These zircons might not only be the oldest minerals on earth, they also show another interesting feature. Their [[oxygen]] [[isotope|isotopic]] composition has been interpreted to indicate that more than 4.4 billion years ago there was already water on the surface of the Earth. This interpretation has been published in top scientific journals<ref>[http://dx.doi.org/10.1016/j.epsl.2008.05.032 Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust]</ref>, <ref>[http://www.physorg.com/news132583481.html Ancient mineral shows early Earth climate tough on continents] ''[[Physorg.com]]'', June 13, 2008</ref> but is the subject of debate. Perhaps the oxygen isotopes and other compositional features (the [[rare earth element]]s) record more recent [[hydrothermal]] alteration of the zircons rather than the composition of the magma at the time of their original crystallization.
==See also==
* [[Heavy mineral sands ore deposits]]
* [[History of Earth]]
* [[Ilmenite]]
* [[list of minerals]]
* [[List of English words of Persian origin]]
* [[Oldest rock]]
* [[Radiometric dating]]
==References==
{{commonscat|Zircon}}
{{Reflist}}
* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
* [http://www.geology.wisc.edu/zircon/zircon_home.html Geochemistry of old zircons]
* [http://mineral.galleries.com/minerals/silicate/zircon/zircon.htm Mineral galleries]
* [http://webmineral.com/data/Zircon.shtml Webmineral]
* [http://www.mindat.org/min-4421.html Mindat]
== Further reading ==
[[Image:Zirconcrystal-model.png|right|150px|thumb|The structure of zircon has a [[space group]] I41/amd.]]
*The most comprehensive and up-to-date work on zircon and its related disciplines is the Mineralogical Society of America monograph published in late 2003: John M. Hanchar & Paul W. O. Hoskin (eds.) (2003). [http://www.minsocam.org/MSA/RIM/Rim53.html "Zircon"]. ''Reviews in Mineralogy and Geochemistry'', '''53'''. ISBN 093995065-0.
* {{cite journal
| author = D. J. Cherniak and E. B. Watson
| year = 2000
| title = Pb diffusion in zircon
| journal = Chemical Geology
| volume = 172
| pages = 5–24
| doi = 10.1016/S0009-2541(00)00233-3
}}
* {{cite journal
| author = A. N. Halliday
| year = 2001
| title = In the beginning…
| journal = Nature
| volume = 409
| pages = 144–145
| doi = 10.1038/35051685 <!--Retrieved from CrossRef by DOI bot-->
}}
* {{cite journal
| author = Hermann Köhler
| year = 1970
| title = Die Änderung der Zirkonmorphologie mit dem Differentiationsgrad eines Granits
| journal = Neues Jahrbuch Mineralogische Monatshefte
| volume = 9
| pages = 405–420
}}
* {{cite journal
| author = K. Mezger and E. J. Krogstad
| year = 1997
| title = Interpretation of discordant U-Pb zircon ages: An evaluation
| journal = Journal of Metamorphic Geology
| volume = 15
| pages = 127–140
| doi = 10.1111/j.1525-1314.1997.00008.x <!--Retrieved from CrossRef by DOI bot-->
}}
* {{cite journal
| author = J. P. Pupin
| year = 1980
| title = Zircon and Granite petrology
| journal = Contributions to Mineralogy and Petrology
| volume = 73
| pages = 207–220
| doi = 10.1007/BF00381441 <!--Retrieved from CrossRef by DOI bot-->
}}
* {{cite journal
| author = Gunnar Ries
| year = 2001
| title = Zirkon als akzessorisches Mineral
| journal = Aufschluss
| volume = 52
| pages = 381–383
| doi = 10.1007/BF00381441
}}
*P. Tondar (1991). ''Zirkonmorphologie als Charakteristikum eines Gesteins.'' Dissertation an der Ludwig-Maximilians-Universität München, 87 pp.
* {{cite journal
| author = G. Vavra
| year = 1990
| title = On the kinematics of zircon growth and its petrogenetic significance: a cathodoluminescence study
| journal = Contributions to Mineralogy and Petrology
| volume = 106
| pages = 90–99
| doi = 10.1007/BF00306410 <!--Retrieved from CrossRef by DOI bot-->
}}
* {{cite journal
| author = John W. Valley, William H. Peck, Elizabeth M. King, Simon A. Wilde
| title = A Cool Early Earth
| journal = Geology
| year = 2002
| volume = 30
| pages = 351–354
| doi = 10.1130/0091-7613(2002)030<0351:ACEE>2.0.CO;2
| url = http://www.geology.wisc.edu/zircon/cool_early/cool_early_home.html
| accessdate=2005-04-11
}}
* {{cite journal
| author = G. Vavra
| year = 1994
| title = Systematics of internal zircon morphology in major Variscan granitoid types
| journal = Contributions to Mineralogy and Petrology
| volume = 117
| pages = 331–344
| doi = 10.1007/BF00307269 <!--Retrieved from CrossRef by DOI bot-->
}}
[[Category:Zirconium minerals]]
[[Category:Nesosilicates]]
[[Category:Refractory materials]]
[[Category:Gemstones]]
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