Editing Silicon dioxide (section)

==Crystalline forms==
SiO<sub>2</sub>, more so than almost any material, exists in many crystalline forms. These forms are called [[polymorphism (materials science)|polymorphs]].
{|class="wikitable"
|+ Crystalline forms of SiO<sub>2</sub><ref name="Wiberg&Holleman"/>
! Form
! Crystal symmetry <br/>[[Pearson symbol]], group no.
! ρ <br />(g/cm<sup>3</sup>)
! width=350|Notes
! Structure
|-
|α-quartz
|[[rhombohedral]] (trigonal)<br/>hP9, P3<sub>1</sub>21 No.152<ref>{{cite journal|journal=[[Journal of Applied Physics]] |year=1982|volume=53|pages=6751–6756|title=Crystal structure and thermal expansion of a-quartz SiO<sub>2</sub> at low temperature|author1=Lager G. A. |author2=Jorgensen J. D. |author3=Rotella F.J. |doi=10.1063/1.330062|issue=10|bibcode = 1982JAP....53.6751L }}</ref>
| 2.648
| Helical chains making individual single crystals optically active; α-quartz converts to β-quartz at 846 K
|[[File:a-quartz.png|100px]]
|-
|β-quartz
|[[Hexagonal crystal system|hexagonal]]<br/>hP18, P6<sub>2</sub>22, No. 180<ref>{{cite journal |doi=10.1016/0022-4596(81)90449-7 |title=The structure of quartz at 25 and 590&nbsp;°C determined by neutron diffraction |year=1981 |last1=Wright |first1=A. F. |last2=Lehmann |first2=M. S. |journal=Journal of Solid State Chemistry |volume=36 |issue=3 |pages=371–80|bibcode = 1981JSSCh..36..371W }}</ref>
| 2.533
| Closely related to α-quartz (with an Si-O-Si angle of 155°) and optically active; β-quartz converts to β-tridymite at 1140 K
|[[File:b-quartz.png|100px]]
|-
|α-tridymite
|[[orthorhombic]]<br/>oS24, C222<sub>1</sub>, No.20<ref name=trid>{{cite journal |doi=10.1524/zkri.1986.177.1-2.27 |title=Structural change of orthorhombic-Itridymite with temperature: A study based on second-order thermal-vibrational parameters |year=1986 |last1=Kihara |first1=Kuniaki |last2=Matsumoto |first2=Takeo |last3=Imamura |first3=Moritaka |journal=Zeitschrift für Kristallographie |volume=177 |issue=1–2 |pages=27–38|bibcode = 1986ZK....177...27K }}</ref>
| 2.265
| Metastable form under normal pressure
|[[File:a-tridymite.png|100px]]
|-
|β-tridymite
| hexagonal<br/>hP12, P6<sub>3</sub>/mmc, No. 194<ref name=trid/>
|
| Closely related to α-tridymite; β-tridymite converts to β-cristobalite at 2010 K
|[[File:b-tridymite.png|100px]]
|-
|α-cristobalite
|[[tetragonal]]<br/>tP12, P4<sub>1</sub>2<sub>1</sub>2, No. 92<ref>{{cite journal|journal=[[American Mineralogist]]|year=1994 |volume=79|pages=9–14|title=The pressure behavior of a cristobalite|url=http://www.geo.arizona.edu/xtal/group/pdf/AM79_9.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://www.geo.arizona.edu/xtal/group/pdf/AM79_9.pdf |archive-date=2022-10-10 |url-status=live|author1=Downs R. T. |author2=Palmer D. C. }}</ref>
| 2.334
| Metastable form under normal pressure
|[[File:a-cristobalite.png|100px]]
|-
|β-cristobalite
|[[Cubic crystal system|cubic]]<br/>cF104, Fd<u style="text-decoration:overline">3</u>m, No.227<ref>{{cite journal |doi=10.1080/00318087508228690 |title=The structures of the β-cristobalite phases of SiO<sub>2</sub> and AlPO<sub>4</sub> |year=1975 |last1=Wright |first1=A. F. |last2=Leadbetter |first2=A. J. |journal=[[Philosophical Magazine]] |volume=31 |issue=6 |pages=1391–401 |bibcode=1975PMag...31.1391W}}</ref>
|
| Closely related to α-cristobalite; melts at 1978 K
|[[File:b-cristobalite.png|100px]]
|-
|[[keatite]]
| tetragonal<br/>tP36, P4<sub>1</sub>2<sub>1</sub>2, No. 92<ref>{{cite journal |doi=10.1524/zkri.1959.112.1-6.409 |title=The crystal structure of keatite, a new form of silica |year=1959 |last1=Shropshire |first1=Joseph |last2=Keat |first2=Paul P. |last3=Vaughan |first3=Philip A. |journal=Zeitschrift für Kristallographie |volume=112 |issue=1–6 |pages=409–13|bibcode = 1959ZK....112..409S }}</ref>
| 3.011
| Si<sub>5</sub>O<sub>10</sub>, Si<sub>4</sub>O<sub>8</sub>, Si<sub>8</sub>O<sub>16</sub> rings; synthesised from glassy silica and alkali at 600–900 K and 40–400 MPa
|[[File:keatite.png|100px]]
|-
|[[moganite]]
|[[monoclinic]]<br/>mS46, C2/c, No.15<ref>{{cite journal |journal=European Journal of Mineralogy |year=1992 |volume=4 |issue=4 |pages=693–706 |title=Crystal structure of moganite: a new structure type for silica |first1=Gerhard |last1=Miehe |first2=Heribert |last2=Graetsch |doi=10.1127/ejm/4/4/0693|bibcode=1992EJMin...4..693M }}</ref>
|
| Si<sub>4</sub>O<sub>8</sub> and Si<sub>6</sub>O<sub>12</sub> rings
|[[File:Moganite.png|100px]]
|-
|[[coesite]]
| monoclinic<br/>mS48, C2/c, No.15<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 |archive-url=https://ghostarchive.org/archive/20221010/http://www.minsocam.org/ammin/AM66/AM66_324.pdf |archive-date=2022-10-10 |url-status=live|author1=Levien L. |author2=Prewitt C. T. }}</ref>
| 2.911
| Si<sub>4</sub>O<sub>8</sub> and Si<sub>8</sub>O<sub>16</sub> rings; 900 K and 3–3.5 GPa
|[[File:coesite.png|100px]]
|-
|[[stishovite]]
| tetragonal<br/>tP6, P4<sub>2</sub>/mnm, No.136<ref>{{cite journal|journal=[[American Mineralogist]] |year=1995|volume=80|issue=5–6|pages=454–456|title=H in rutile-type compounds: II. Crystal chemistry of Al substitution in H-bearing stishovite |author1=Smyth J. R. |author2=Swope R. J. |author3=Pawley A. R. |url=http://rruff.geo.arizona.edu/doclib/am/vol80/AM80_454.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://rruff.geo.arizona.edu/doclib/am/vol80/AM80_454.pdf |archive-date=2022-10-10 |url-status=live|doi=10.2138/am-1995-5-605|bibcode=1995AmMin..80..454S|s2cid=196903109}}</ref>
| 4.287
| One of the densest (together with seifertite) polymorphs of silica; [[rutile]]-like with 6-fold coordinated Si; 7.5–8.5 GPa
|[[File:stishovite.png|100px]]
|-
|[[seifertite]]
| orthorhombic<br/>oP, Pbcn<ref>{{cite journal|author1=Dera P. |author2=Prewitt C. T. |author3=Boctor N. Z. |author4=Hemley R. J. |journal=[[American Mineralogist]] |volume=87|issue=7 |year=2002|page=1018|title=Characterization of a high-pressure phase of silica from the Martian meteorite Shergotty|url=http://rruff.geo.arizona.edu/AMS/authors/Boctor%20N%20Z|doi=10.2138/am-2002-0728 |bibcode=2002AmMin..87.1018D |s2cid=129400258 |url-access=subscription }}</ref>
| 4.294
| One of the densest (together with stishovite) polymorphs of silica; is produced at pressures above 40 GPa.<ref>[http://www.mindat.org/min-26715.html Seifertite]. Mindat.org.</ref>
|[[File:SeifertiteStructure.png|100px]]
|-
|[[melanophlogite]]
| cubic (cP*, P4<sub>2</sub>32, No.208)<ref name="mel">{{cite journal|vauthors=Skinner BJ, Appleman DE|year=1963|title=Melanophlogite, a cubic polymorph of silica|url=http://www.minsocam.org/ammin/AM48/AM48_854.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://www.minsocam.org/ammin/AM48/AM48_854.pdf |archive-date=2022-10-10 |url-status=live|journal=[[American Mineralogist|Am. Mineral.]]|volume=48|pages=854–867}}</ref> or<br>tetragonal (P4<sub>2</sub>/nbc)<ref>{{cite journal |author1=Nakagawa T. |author2=Kihara K. |author3=Harada K. |journal=[[American Mineralogist]] |volume=86|issue=11–12 |year=2001|page=1506|title=The crystal structure of low melanophlogite|url=http://rruff.geo.arizona.edu/AMS/minerals/Melanophlogite|doi=10.2138/am-2001-11-1219 |bibcode=2001AmMin..86.1506N |s2cid=53525827 |url-access=subscription }}</ref>
| 2.04
| Si<sub>5</sub>O<sub>10</sub>, Si<sub>6</sub>O<sub>12</sub> rings; mineral always found with hydrocarbons in interstitial spaces - a [[clathrasil]] (silica [[Clathrate compound|clathrate]])<ref>{{cite book|author=Rosemarie Szostak|year=1998|title=Molecular sieves: Principles of Synthesis and Identification|publisher=Springer|isbn=978-0-7514-0480-7|url=https://books.google.com/books?id=lteintjA2-MC}}</ref>
|[[File:MelanophlogiteStucture.png|100px]]
|-
| fibrous<br/> W-silica<ref name="Greenwood"/>
| orthorhombic<br/>oI12, Ibam, No.72<ref>{{cite journal |doi=10.1002/zaac.19542760110 |title=Über Siliciumchalkogenide. VI. Zur Kenntnis der faserigen Siliciumdioxyd-Modifikation |year=1954 |last1=Weiss |first1=Alarich |last2=Weiss |first2=Armin |journal=Zeitschrift für Anorganische und Allgemeine Chemie |volume=276 |issue=1–2 |pages=95–112}}</ref>
| 1.97
| Like [[silicon sulfide|SiS<sub>2</sub>]] consisting of edge-sharing chains, melts at ~1700 K
|[[File:SiS2typeSilica.png|100px]]
|-
| [[2D silica]]<ref>{{cite journal|doi=10.1038/srep03482|pmid=24336488|pmc=3863822|title=Defects in bilayer silica and graphene: common trends in diverse hexagonal two-dimensional systems|journal=Scientific Reports|volume=3|pages=3482|year=2013|last1=Björkman|first1=T|last2=Kurasch|first2=S|last3=Lehtinen|first3=O|last4=Kotakoski|first4=J|last5=Yazyev|first5=O. V.|last6=Srivastava|first6=A|last7=Skakalova|first7=V|last8=Smet|first8=J. H.|last9=Kaiser|first9=U|last10=Krasheninnikov|first10=A. V.|bibcode=2013NatSR...3E3482B}}</ref>
| hexagonal
|
| Sheet-like bilayer structure
|[[File:2D silica structure.png|100px]]
|}