Editing Zircon (section)

==Properties==
[[Image:zircon microscope.jpg|left|150px|thumb|Optical microscope photograph; the length of the crystal is about 250 [[μm]]]]

Zircon is common in the [[Crust (geology)|crust]] of Earth. It occurs as a common [[accessory mineral]] in [[igneous rock]]s (as primary crystallization products), in [[metamorphic rock]]s and as detrital grains in [[sedimentary rock]]s.<ref name=HBM/> Large zircon crystals are rare. Their average size in [[granitoid|granite]] rocks is about {{cvt|0.1|–|0.3|mm}}, but they can also grow to sizes of several cm, especially in [[mafic]] [[pegmatite]]s and [[carbonatite]]s.<ref name=HBM/> Zircon is fairly hard (with a Mohs hardness of 7.5) and chemically stable, and so is highly resistant to weathering. It also is resistant to heat, so that detrital zircon grains are sometimes preserved in igneous rocks formed from melted sediments.<ref>{{cite book|last=Nesse|first=William D.|title=Introduction to mineralogy|date=2000|publisher=Oxford University Press|location=New York|isbn=9780195106916|pages=313–314}}</ref> Its resistance to weathering, together with its relatively high specific gravity (4.68), make it an important component of the heavy mineral fraction of sandstones.<ref name="hurlbut-klein"/>

Because of their [[uranium]]<ref name="Jackson-2019">{{Cite journal |last1=Jackson |first1=Robert A. |last2=Montenari |first2=Michael |date=2019 |title=Computer modeling of Zircon (ZrSiO4)—Coffinite (USiO4) solid solutions and lead incorporation: Geological implications |url=https://www.sciencedirect.com/science/article/abs/pii/S246851781930005X |journal=Stratigraphy & Timescales |volume=4 |pages=217–227 |doi=10.1016/bs.sats.2019.08.005 |isbn=9780128175521 |s2cid=210256739 |via=Elsevier Science Direct}}</ref> and [[thorium]] content, some zircons undergo [[metamictization]]. Connected to internal radiation damage, these processes partially disrupt the crystal structure and partly explain the highly variable properties of zircon. As zircon becomes more and more modified by internal radiation damage, the density decreases, the crystal structure is compromised, and the color changes.{{sfn|Nesse|2000|pp=93–94}}

Zircon occurs in many colors, including reddish brown, yellow, green, blue, gray, and colorless.<ref name=HBM/> The color of zircons can sometimes be changed by heat treatment. Common brown zircons can be transformed into colorless and blue zircons by heating to {{cvt|800|to|1000|C}}.<ref name=Gemdat>{{cite web|url=http://www.gemdat.org/gem-4421.html|title=Zircon gemstone information|website=www.gemdat.org|access-date=April 29, 2018}}</ref> In geological settings, the development of pink, red, and purple zircon occurs after hundreds of millions of years, if the crystal has sufficient trace elements to produce [[F-Center|color centers]]. Color in this red or pink series is annealed in geological conditions above temperatures of around {{cvt|400|C||}}.<ref>{{cite journal|doi=10.1016/S0040-1951(02)00054-9|title=Integration of zircon color and zircon fission-track zonation patterns in orogenic belts: Application to the Southern Alps, New Zealand |journal=Tectonophysics |volume=349 |issue=1–4 |pages=203–219 |year=2002 |last1=Garver |first1=John I. |last2=Kamp |first2=Peter J.J. |bibcode=2002Tectp.349..203G |citeseerx=10.1.1.570.3912}}</ref>

Structurally, zircon consists of parallel chains of alternating silica tetrahedra (silicon ions in fourfold coordination with oxygen ions) and zirconium ions, with the large zirconium ions in eightfold coordination with oxygen ions.{{sfn|Nesse|2000|p=313}}