View source for Coesite

{{short description|Silica mineral, rare polymorph of quartz}}
{{Infobox mineral
| name        = Coesite
| boxwidth    =
| boxbgcolor  =
| image       = Coesiteimage.jpg
| imagesize   = 260px
| alt         =
| caption     = Crossed-polars image of coesite grain (gray) ~1&nbsp;mm across in [[eclogite]]. Small, colored [[inclusion (mineral)|inclusion]] is [[pyroxene]]. Polycrystalline rim is quartz.
| category    = [[Tectosilicate]] [[minerals]], [[quartz]] [[Mineral group|group]]
| molweight   = 60.0843&nbsp;g/mol
| formula     = {{chem2|SiO2}}
| IMAsymbol=Coe<ref>{{cite journal |last=Warr|first=L. N. |date=2021 |title=IMA–CNMNC approved mineral symbols |journal=[[Mineralogical Magazine]] |volume=85 |issue=3 |pages=291–320 |doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616 |doi-access=free}}</ref>
| strunz      = 4.DA.35
| system      = [[monoclinic crystal system|Monoclinic]]
| class       = Prismatic (2/m) <br /><small>(same [[Hermann–Mauguin notation|H–M symbol]])</small>
| symmetry    = ''C2/c''
| unit cell   = ''a'' = 7.143<br>''b'' = 12.383<br>''c'' = 7.143&nbsp;[Å]<br>β = 120.00°<br>''Z'' = 16
| color       = Colorless
| colour      =
| habit       = [[inclusion (mineral)|Inclusions]] in UHP metamorphic minerals up to 3&nbsp;mm in size
| twinning    =
| cleavage    = 
| fracture    = [[conchoidal fracture|Conchoidal]]
| tenacity    = [[brittleness|Brittle]]
| mohs        = 7.5-8
| luster      = Vitreous
| streak      = White
| diaphaneity = Transparent
| gravity     =
| density     = 2.92 (calculated)
| polish      =
| opticalprop = Biaxial
| refractive  = ''n''<sub>x</sub> = 1.594<br>''n''<sub>y</sub> = 1.595<br>''n''<sub>z</sub> = 1.599
| birefringence = +0.006
| pleochroism = 
| 2V          = 60–70
| dispersion  =
| extinction  =
| length fast/slow =
| fluorescence =
| absorption  =
| melt        =
| fusibility  =
| diagnostic  =
| solubility  =
| impurities  =
| alteration  =
| other       =
| prop1       =
| references = <ref>{{cite book |editor1=Anthony, John W. |editor2=Bideaux, Richard A. |editor3=Bladh, Kenneth W. |editor4=Nichols, Monte C. |title=Handbook of Mineralogy |publisher=[[Mineralogical Society of America]] |location=[[Chantilly, Virginia]] |chapter-url=https://handbookofmineralogy.org/pdfs/coesite.pdf |chapter=Coesite |date=1995 |access-date=December 5, 2011 |isbn=0962209716 |volume=2 (Silica, Silicates)}}</ref>
}}

'''Coesite''' ({{IPAc-en|ˈ|k|oʊ|s|aɪ|t}})<ref>{{cite Dictionary.com|coesite}}</ref> is a form ([[polymorphism (materials science)|polymorph]]) of [[silicon dioxide]] ([[silicon|Si]][[oxide|O]]<sub>2</sub>) that is formed when very high pressure (2–3 [[gigapascal]]s), and moderately high temperature ({{cvt|700|C|F|disp=comma|sigfig=2}}), are applied to [[quartz]]. Coesite was first synthesized by Loring Coes, Jr., a chemist at the [[Norton Company]], in 1953.<ref name="C53">{{cite journal |last=Coes, Jr.|first=L. |date=31 July 1953 |title=A New Dense Crystalline Silica |journal=[[Science (journal)|Science]] |volume=118 |issue=3057 |pages=131–132 |doi=10.1126/science.118.3057.131 |pmid=17835139 |bibcode=1953Sci...118..131C }} The word ''coesite'' is pronounced as "Coze-ite", after chemist Loring Coes, Jr.</ref><ref>{{cite book |first=Robert M.|last=Hazen |author-link=Robert Hazen |title=The Diamond Makers |date=22 July 1999 |publisher=[[Cambridge University Press]] |isbn=978-0-521-65474-6 |page=91 |url=https://books.google.com/books?id=fNJQok6N9_MC&pg=PA91 |access-date=2012-06-06}}</ref>

==Occurrences==

In 1960, a natural occurrence of coesite was reported by [[Edward C. T. Chao]],<ref>{{cite journal|doi=10.1126/science.132.3421.220|title=First Natural Occurrence of Coesite|year=1960|last1=Chao|first1=E. C. T.|last2=Shoemaker|first2=E. M.|last3=Madsen|first3=B. M.|journal=Science|volume=132|pages=220–2|pmid=17748937|issue=3421|bibcode=1960Sci...132..220C|s2cid=45197811}}</ref> in collaboration with [[Eugene Shoemaker]], from [[Barringer Crater]], in Arizona, US, which was evidence that the crater must have been formed by an impact. After this report, the presence of coesite in unmetamorphosed rocks was taken as evidence of a meteorite [[impact event]] or of an [[atomic bomb]] explosion. It was not expected that coesite would survive in high pressure [[metamorphic rock]]s.
[[File:P-T Diagram for SiO2.svg|left|frameless|400x400px]]
In metamorphic rocks, coesite was initially described in [[eclogite]] [[xenoliths]] from the [[mantle (geology)|mantle]] of the Earth that were carried up by ascending [[magma]]s; [[kimberlite]] is the most common host of such xenoliths.<ref>{{cite journal|doi=10.1016/0012-821X(77)90012-7|bibcode=1977E&PSL..34..284S|title=A coesite-sanidine grospydite from the Roberts Victor kimberlite|year=1977|last1=Smyth|first1=Joseph R.|last2=Hatton|first2=C.J.|journal=Earth and Planetary Science Letters|volume=34|issue=2|pages=284}}</ref> In metamorphic rocks, coesite  is now recognized as one of the best mineral indicators of metamorphism at very high pressures (UHP, or [[ultrahigh-pressure metamorphism]]).<ref name="ReferenceA">{{cite journal|doi=10.1007/BF00381838|title=Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences|year=1984|last1=Chopin|first1=Christian|journal=Contributions to Mineralogy and Petrology|volume=86|pages=107–118|bibcode=1984CoMP...86..107C|issue=2|s2cid=128818052}}</ref> Such UHP metamorphic rocks record [[subduction]] or continental collisions in which [[crust (geology)|crustal]] rocks are carried to depths of {{convert|70|km|abbr=on}} or more.  Coesite is formed at pressures above about 2.5 GPa (25 kbar) and temperature above about 700&nbsp;°C. This corresponds to a depth of about 70&nbsp;km in the Earth. It can be preserved as mineral inclusions in other phases because as it partially reverts to [[quartz]], the quartz rim exerts pressure on the core of the grain, preserving the metastable grain as tectonic forces uplift and expose these rock at the surface. As a result, the grains have a characteristic texture of a polycrystalline quartz rim (see infobox figure).

Coesite has been identified in UHP metamorphic rocks around the world, including the western [[Geology of the Alps|Alps]] of Italy at Dora Maira,<ref name="ReferenceA"/> the [[Ore Mountains]] of Germany,<ref>{{cite journal| author= Massonne, H.-J. |year=2001|title= First find of coesite in the ultrahigh-pressure metamorphic area of the central Erzgebirge, Germany|journal= European Journal of Mineralogy|volume= 13|pages= 565–570| doi= 10.1127/0935-1221/2001/0013-0565| issue= 3|bibcode= 2001EJMin..13..565M}}</ref> the Lanterman Range of Antarctica,<ref>{{cite journal|author1=Ghiribelli, B. |author2=Frezzotti, M.L. |author3=Palmeri, R. |name-list-style=amp |year=2002|title= Coesite in eclogites of the Lanterman Range (Antarctica): Evidence from textural and Raman studies|journal= European Journal of Mineralogy|volume= 14|pages=355–360| doi=10.1127/0935-1221/2002/0014-0355| issue=2|bibcode=2002EJMin..14..355G}}</ref> in the [[Kokchetav Massif]] of Kazakhstan,<ref>{{cite journal|author1=Korsakov, A.V. |author2=Shatskiy, V. S.|author3=Sobolev N.V. |name-list-style=amp |year=1998|title= Первая находка коэсита в эклогитах Кокчетавского массива (First occurrence of coesite in eclogites from the Kokchetav Massif)|journal= Doklady Earth Sciences |volume=359|pages= 77–81}}</ref> in the [[Geology of Norway|Western Gneiss]] region of Norway,<ref>{{cite journal| author=Smith, D.C. |year=1984|title= Coesite in clinopyroxene in the Caledonides and its implications for geodynamics|journal= Nature |volume=310|pages= 641–644| doi=10.1038/310641a0| issue=5979|bibcode = 1984Natur.310..641S |s2cid=4330257}}</ref> the [[Dabie Mountains|Dabie-Shan]] Range in Eastern China,<ref>{{cite journal|author1=Schertl, H.-P.|author2=Okay, A.I. |year=1994|title= A coesite inclusion in dolomite in Dabie Shan, China: petrological and rheological significance|url=http://eurjmin.geoscienceworld.org/content/6/6/995.short|journal= Eur. J. Mineral.|volume= 6|pages= 995–1000|issue=6|doi=10.1127/ejm/6/6/0995|bibcode=1994EJMin...6..995S|url-access=subscription}}</ref><ref>{{Cite journal|last1=Wang|first1=Xiaomin|last2=Liou|first2=J. G.|last3=Mao|first3=H. K.|date=1989-12-01|title=Coesite-bearing eclogite from the Dabie Mountains in central China|url=https://doi.org/10.1130/0091-7613(1989)0172.3.CO;2|journal=Geology|volume=17|issue=12|pages=1085–1088|doi=10.1130/0091-7613(1989)017<1085:CBEFTD>2.3.CO;2|bibcode=1989Geo....17.1085W|issn=0091-7613|url-access=subscription}}</ref> the [[Geology of the Himalaya|Himalayas]] of Eastern Pakistan,<ref>{{cite journal| author1=O'Brien, P.J.|author2=N. Zotov|author3=R. Law|author4=M.A. Khan|author5=M.Q. Jan |year=2001|title= Coesite in Himalayan eclogite and implications for models of India-Asia collision|journal= Geology |volume=29|pages= 435–438| doi=10.1130/0091-7613(2001)029<0435:CIHEAI>2.0.CO;2| issue=5|bibcode = 2001Geo....29..435O }}</ref> and in the [[Appalachian Mountains]] of Vermont.<ref>{{cite journal|author=Joseph Gonzalez|author2=Suzanne Baldwin|author2-link=Suzanne Baldwin|author3=Jay B Thomas|author4=William O Nachlas|author5=Paul G Fitzgerald |year=2019|title=First Discovery of Coesite in the Appalachians: Characterization of Prograde Metamorphism in a Taconic Metapelite|journal=AGU Fall Meeting |volume=2019|pages=V51B–03|bibcode=2019AGUFM.V51B..03G|url=https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/552005}}</ref><ref>{{cite journal|author=Joseph Gonzalez|author2=Suzanne Baldwin|author2-link=Suzanne Baldwin|author3=Jay B Thomas|author4=William O Nachlas|author5=Paul G Fitzgerald |year=2020|title=Evidence for ultrahigh-pressure metamorphism discovered in the Appalachian orogen|journal=Geology|volume=48|issue=10|pages=947–951|doi=10.1130/G47507.1|bibcode=2020Geo....48..947G|s2cid=224854495}}</ref>

==Crystal structure==
[[File:coesite.png|150px|thumb|left|Atomic structure of coesite]]

Coesite is a [[tectosilicate]] with each silicon atom surrounded by four oxygen atoms in a tetrahedron. Each oxygen atom is then bonded to two Si atoms to form a framework. There are two crystallographically distinct Si atoms and five different oxygen positions in the unit cell. Although the unit cell is close to being [[hexagonal]] in shape ("a" and "c" are nearly equal and β nearly 120°), it is inherently [[monoclinic]] and cannot be hexagonal. The crystal structure of coesite is similar to that of [[feldspar]] and consists of four [[silicon dioxide]] [[tetrahedron|tetrahedra]] arranged in Si<sub>4</sub>O<sub>8</sub> and Si<sub>8</sub>O<sub>16</sub> rings. The rings are further arranged into chains. This structure is [[Metastability in molecules|metastable]] within the stability field of quartz: coesite will eventually decay back into quartz with a consequent volume increase, although the [[metamorphic reaction]] is very slow at the low temperatures of the Earth's surface. The crystal symmetry is monoclinic C2/c, No.15, [[Pearson symbol]] mS48.<ref>{{cite journal|journal=American Mineralogist|year=1981|volume=66|pages=324–333|title=High-pressure crystal structure and compressibility of coesite|url=http://www.minsocam.org/ammin/AM66/AM66_324.pdf|author1=Levien L.|author2=Prewitt C.T.|access-date=2009-12-15|archive-url=https://web.archive.org/web/20160604062422/http://www.minsocam.org/ammin/AM66/AM66_324.pdf|archive-date=2016-06-04|url-status=dead}}</ref>

==See also==
{{Portal|Science|Chemistry
}}
* [[Seifertite]], forming at higher pressure than stishovite
* [[Stishovite]], a higher-pressure polymorph

==References==
{{reflist}}

==External links==
* [https://web.archive.org/web/20040305170121/http://mineral.galleries.com/minerals/Silicate/COESITE/COESITE.htm Coesite page]
* [https://web.archive.org/web/20120718045423/http://barringercrater.com/education/ Barringer Meteor Crater science education page]
{{Impact cratering on Earth}}
{{Silica minerals}}

[[Category:Impact event minerals]]
[[Category:Silica polymorphs]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 15]]
[[Category:Silicon dioxide]]