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Infobox - Strunz classification - added "(Oxides)" |
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{{Short description|Tetragonal form of silicon dioxide}}
{{Infobox mineral
| name = Stishovite
| category =
| boxwidth =
| boxbgcolor =
| image = stishovite.png
| imagesize =
| caption = Crystal structure of stishovite
| formula = SiO<sub>2</sub>
| IMAsymbol = Sti<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.40 (Oxides)
| system = [[Tetragonal]]
|
| symmetry = ''P''4<sub>2</sub>/mnm (No. 136)
| unit cell = ''a'' = 4.1772(7) Å, <br />''c'' = 2.6651(4)
| color = Colorless (when pure)
| habit =
| twinning =
| cleavage =
| fracture =
| mohs =
| luster = Vitreous
| refractive = ''n''<sub>ω</sub> = 1.799–1.800 <br />''n''<sub>ε</sub> = 1.826–1.845
| opticalprop = Uniaxial (+)
| birefringence = δ = 0.027
| pleochroism =
| streak =
| gravity = 4.
| density =
| melt = (decomposes)
| fusibility =
| diagnostic =
| solubility =
| diaphaneity = Transparent to translucent
| other =
| references = <ref name=HBM>{{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]]|place= Chantilly, VA, US|url=http://rruff.geo.arizona.edu/doclib/hom/stishovite.pdf
}}
'''Stishovite''' is an extremely hard, dense [[tetragonal]] form ([[Polymorphism (materials science)|polymorph]]) of [[silicon dioxide]]. It is very rare on the Earth's surface, however, it may be a predominant form of silicon dioxide in the Earth, especially in the lower mantle.<ref>Dmitry L. Lakshtanov et al. "The post-stishovite phase transition in hydrous alumina-bearing SiO<sub>2</sub> in the lower mantle of the earth" PNAS 2007 104 (34) 13588-13590; {{doi|10.1073/pnas.0706113104}}</ref>▼
▲'''Stishovite''' is an extremely hard, dense [[tetragonal]] form ([[Polymorphism (materials science)|polymorph]]) of [[silicon dioxide]]. It is very rare on the Earth's surface
Stishovite was named after {{ill|Sergey M. Stishov|ru|Стишов, Сергей Михайлович}}, a Russian high-pressure physicist who first synthesized the mineral in 1961. It was discovered in [[Meteor Crater]] in 1962 by [[Edward C. T. Chao]].<ref name="Fleischer1962">{{cite journal |last1=Fleischer |first1=Michael|year=1962|title=New mineral names |journal=American Mineralogist |volume=47 |issue=2 |pages=172–174 |publisher=Mineralogical Society of America |url=http://rruff.info/uploads/AM47_805.pdf }}</ref>
Unlike other silica polymorphs, the crystal structure of stishovite resembles that of [[rutile]] (TiO<sub>2</sub>). The silicon in stishovite adopts an octahedral coordination geometry, being bound to six oxides. Similarly, the oxides are three-connected, unlike low-pressure forms of SiO<sub>2</sub>. In most silicates, silicon is tetrahedral, being bound to four oxides.<ref name="Ross1990">{{cite journal |last1=Ross |first1=Nancy L.|year=1990|title=High pressure crystal chemistry of stishovite|journal=American Mineralogist |volume=75 |issue=7 |pages=739–747 |publisher=Mineralogical Society of America Stishovite can be separated from quartz by applying [[hydrogen fluoride]] (HF); unlike quartz, stishovite will not react.<ref name="Fleischer1962"/>
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==Synthesis==
Until recently, the only known occurrences of stishovite in nature formed at the very high shock pressures (>100 kbar, or 10 GPa) and temperatures (> 1200 °C) present during [[hypervelocity]] [[meteorite]] [[impact
At 4.287 g/cm<sup>3</sup>, it is the second densest polymorph of silica, after [[seifertite]]. It has [[tetragonal]] crystal symmetry, P4<sub>2</sub>/mnm, No. 136, [[Pearson symbol]] tP6.<ref>{{cite journal|journal=American Mineralogist|year=1995 |volume=80|pages=454–456|title=H in rutile-type compounds: II. Crystal chemistry of Al substitution in H-bearing stishovite|url=http://rruff.geo.arizona.edu/doclib/am/vol80/AM80_454.pdf|author1=Smyth J. R. |author2=Swope R. J. |author3=Pawley A. R. |issue=5–6 |bibcode=1995AmMin..80..454S|doi=10.2138/am-1995-5-605|s2cid=196903109 }}</ref>▼
▲Until recently, the only known occurrences of stishovite in nature formed at the very high shock pressures (>100 kbar or 10 GPa) and temperatures (> 1200 °C) present during hypervelocity [[meteorite]] [[impact crater|impact]] into [[quartz]]-bearing [[Rock (geology)|rock]]. Minute amounts of stishovite have been found within diamonds,<ref>{{cite journal|doi=10.1016/j.epsl.2007.04.041|title=Inclusions of nanocrystalline hydrous aluminium silicate "Phase Egg" in superdeep diamonds from Juina (Mato Grosso State, Brazil) |year=2007 |last1=Wirth |first1=R|last2=Vollmer|first2=C|last3=Brenker|first3=F|last4=Matsyuk|first4=S|last5=Kaminsky|first5=F|journal=Earth and Planetary Science Letters|volume=259|pages=384 |bibcode=2007E&PSL.259..384W|issue=3–4}}</ref> and post-stishovite phases were identified within ultra-high-pressure mantle rocks.<ref>{{cite journal|doi=10.1016/j.epsl.2007.08.010|url=http://micron.ucr.edu/public/KNB-papers/Liu-et-al-2007.pdf|title=Evidence of former stishovite in metamorphosed sediments, implying subduction to >350 km|year=2007|last1=Liu|first1=L|last2=Zhang|first2=J |last3=Greenii|first3=H |last4=Jin|first4=Z|last5=Bozhilov|first5=K|journal=Earth and Planetary Science Letters|bibcode=2007E&PSL.263..180L|volume=263|issue=3–4|pages=180}}</ref> Stishovite may also be synthesized by duplicating these conditions in the laboratory, either isostatically or through shock (see [[shocked quartz]]).<ref>{{cite journal|title=Discovery of hardest known oxide|year=1996|journal=Nature|volume=383|pages=401|doi=10.1038/383401a0 |author=J. M. Léger, J. Haines, M. Schmidt, J. P. Petitet, A. S. Pereira & J. A. H. da Jornada|issue=6599|bibcode = 1996Natur.383..401L }}</ref>
▲At 4.287 g/cm<sup>3</sup> it is second densest polymorph of silica, after [[seifertite]]. It has [[tetragonal]] crystal symmetry, P4<sub>2</sub>/mnm, No.136, [[Pearson symbol]] tP6.<ref>{{cite journal|journal=American Mineralogist|year=1995 |volume=80|pages=454–456|title=H in rutile-type compounds: II. Crystal chemistry of Al substitution in H-bearing stishovite|url=http://rruff.geo.arizona.edu/doclib/am/vol80/AM80_454.pdf|author1=Smyth J.R. |author2=Swope R.J. |author3=Pawley A.R. }}</ref>
==See also==
* [[Coesite]], a related mineral
* [[Thaumasite]], another rare mineral with hexacoordinated octahedral silica
==References==
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==External links==
* [https://web.archive.org/web/20040216002413/http://mineral.galleries.com/minerals/oxides/stishovi/stishovi.htm Properties of stishovite]
* [http://www.umich.edu/~gs265/meteor.htm Stishovite's origin in meteor impacts]
{{Silica minerals}}
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[[Category:Superhard materials]]
[[Category:Impact event minerals]]
[[Category:Tetragonal minerals]]
[[Category:Minerals in space group 136]]
[[Category:Silica polymorphs]]
[[Category:Soviet inventions]]
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