Editing Shocked quartz

{{Short description|Form of the mineral quartz, found in nuclear test sites and meteor impact zones}}
{{Distinguish|Fused quartz}}
[[File:Suvasvesi shocked quartz.jpg|thumb|right|upright=1.2|[[Photomicrograph]] of shocked quartz]]
'''Shocked quartz''' is a form of [[quartz]] that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the [[crystalline structure]] of quartz is deformed along planes inside the crystal. These planes, which show up as lines under a microscope, are called [[planar deformation features]] (PDFs), or shock lamellae.

==Discovery==
Shocked quartz was discovered following [[underground nuclear weapons testing]], which generated the intense pressures required to alter the quartz lattice. [[Eugene Shoemaker]] showed that shocked quartz is also found inside [[Impact crater|craters]] created by [[Meteoroid|meteor]] impact, such as the [[Barringer Crater]] and [[Chicxulub crater]].<ref>{{cite report |author=Eugene Merle Shoemaker|author-link=Eugene Merle Shoemaker|title=Impact mechanics at Meteor crater, Arizona |website=US Geological Survey |doi=10.3133/ofr59108 |doi-access=free |date=1959}}</ref> The presence of shocked quartz supports that such craters were formed by impact, because a volcanic eruption would not generate the required pressure.<ref>{{cite conference|last1=de Silva|first1=SL|last2=Sharpton|first2=VL|title = Explosive Volcanism, Shock Metamorphism and the K-T Boundary|conference = Global Catastrophes in Earth History: An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality|year = 1988|series = LPI Contributions|volume = 673|page = 38|bibcode=1988LPICo.673...38D}}</ref>

Lightning is now known to contribute to the surface record of shocked quartz grains, complicating identification of [[hypervelocity impact]] features.<ref name="ammin.geoscienceworld.org">{{cite journal|url=http://ammin.geoscienceworld.org/content/100/7/1645.abstract |title=Lightning-induced shock lamellae in quartz |publisher=Ammin.geoscienceworld.org |date=2015-07-01 |doi=10.2138/am-2015-5218 |access-date=2018-08-07|last1=Gieré |first1=Reto |last2=Wimmenauer |first2=Wolfhard |last3=Müller-Sigmund |first3=Hiltrud |last4=Wirth |first4=Richard |last5=Lumpkin |first5=Gregory R. |last6=Smith |first6=Katherine L. |journal=American Mineralogist |volume=100 |issue=7 |pages=1645–1648 |bibcode=2015AmMin.100.1645G |s2cid=130973907 |url-access=subscription }}</ref>

==Formation==
[[File:820qtz.jpg|thumb|right|Photomicrograph of a shocked quartz grain (0.13&nbsp;mm across) from the [[Chesapeake Bay impact crater]], showing shock lamellae]]
Shocked quartz is usually associated in nature with two high-pressure [[polymorphism (materials science)|polymorphs]] of [[silicon dioxide]]: [[coesite]] and [[stishovite]]. These polymorphs have a crystal structure different from standard quartz. This structure can be formed only by intense pressure (more than 2 [[Pascal (unit)|gigapascals]]), but at moderate temperatures. Coesite and stishovite are usually viewed as indicative of [[impact event]]s or [[eclogite facies]] metamorphism (or [[nuclear explosion]]), but are also found in sediments prone to [[lightning]] strikes and in [[fulgurite]]s.<ref>{{cite journal |last=Melosh |first=H.J. |title=Impact geologists, beware! |journal=Geophysical Research Letters |volume=44 |issue=17 |pages=8873–8874 |doi=10.1002/2017GL074840 |year=2017 |bibcode=2017GeoRL..44.8873M |s2cid=134575031 }}</ref><ref name="ammin.geoscienceworld.org"/>

==Occurrence==
Shocked quartz is found worldwide, and occurs in the thin [[Cretaceous–Paleogene boundary]] layer, which occurs at the contact between [[Cretaceous]] and [[Paleogene]] rocks. This is further evidence (in addition to [[iridium]] enrichment) that the transition between the two geologic periods was caused by a large impact.<ref>{{cite conference|last=Bohor|first=BF|title=Shocked Quartz and More: Impact Signatures in K-T Boundary Clays and Claystones|conference=Global Catastrophes in Earth History: An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality|year = 1988|series=LPI Contributions|volume=673|page=17|bibcode=1988LPICo.673...17B}}</ref>

Lightning also generates [[planar deformation features]] in quartz and is capable of propagating appropriate pressure/temperature gradients in rocks and sediments alike.<ref>{{cite journal |last1=Gieré |first1=Reto |last2=Wimmenauer |first2=Wolfhard |last3=Müller-Sigmund |first3=Hiltrud |last4=Wirth |first4=Richard |last5=Lumpkin |first5=Gregory R. |last6=Smith |first6=Katherine L. |title=Lightning-induced shock lamellae in quartz |url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/100/7/1645/40585/Lightning-induced-shock-lamellae-in-quartz |journal=American Mineralogist |year=2015 |volume=100 |issue=7 |pages=1645–1648 |doi=10.2138/am-2015-5218 |bibcode=2015AmMin.100.1645G |s2cid=130973907 |url-access=subscription }}</ref> This very common mechanism may significantly contribute to the accumulation of shocked quartz in the geologic record. Mantle xenoliths and sediments derived from them may contain coesite or stishovite.<ref>{{cite journal|first1=JG|last1=Liou|first2=WG|last2=Ernst|first3=RY|last3=Zhang|first4=T|last4=Tsujimori|first5=BM|last5=Jahn|title=Ultrahigh-pressure minerals and metamorphic terranes – The view from China|journal=Journal of Asian Earth Sciences|volume=35|issue=3–4|year=2009|pages=199–231|doi=10.1016/j.jseaes.2008.10.012|bibcode=2009JAESc..35..199L}}</ref>

Though shocked quartz is only recently recognized, [[Eugene Shoemaker]] discovered it prior to its crystallographic description in building stones in the [[Bavaria]]n town of [[Nördlingen]], derived from [[shock metamorphism|shock-metamorphic]] rocks, such as [[breccia]] and [[pseudotachylite]], of [[Nördlinger Ries|Ries crater]].<ref name=Shoemaker_1961>{{cite journal|first1=EM|last1=Shoemaker|first2=ECT|last2=Chao|year=1961|title=New Evidence for the Impact Origin of the Ries Basin, Bavaria, Germany|journal=J. Geophys. Res.|volume=66|issue=10|pages=3371–3378|doi=10.1029/JZ066i010p03371|bibcode=1961JGR....66.3371S}}</ref><ref name=Cokinos_2009>{{cite book|title=The Fallen Sky|last=Cokinos|first=C|date=2009|publisher=Penguin|url=https://books.google.com/books?id=1uFRVyFxA04C&q=coesite&pg=PT246|isbn=978-1-101-13322-4}}</ref>

== See also ==
* [[Lechatelierite]]
* [[Seifertite]]
* [[Shatter cone]]
* [[Shock metamorphism]]

==References==
{{Reflist|colwidth=33em}}

==External links==
* [http://arquivo.pt/wayback/20160522184111/http://www.scn.org/~bh162/shocked_quartz.html Shocked quartz page]
* [https://web.archive.org/web/20040305170121/http://mineral.galleries.com/minerals/Silicate/COESITE/COESITE.htm Coesite page]
* [https://web.archive.org/web/20040216002413/http://mineral.galleries.com/minerals/oxides/stishovi/stishovi.htm Stishovite page]

{{Silica minerals}}
{{Impact cratering on Earth}}

[[Category:Quartz varieties]]
[[Category:Impact geology]]