Editing Silicon dioxide (section)

==Natural occurrence==
===Geology===
[[File:P-T Diagram for SiO2.svg|left|frameless|400x400px]]
{{chem2|SiO2}} is most commonly encountered in nature as [[quartz]], which comprises more than 10% by mass of the Earth's crust.<ref name="Ull">{{Ullmann|title=Silica|vauthors=Flörke OW, Graetsch HA, Brunk F, Benda L, Paschen S, Bergna HE, Roberts WO, Welsh WA, Libanati C, Ettlinger M, Kerner D, Maier M, Meon W, Schmoll R, Gies H, Schiffmann D|year=2018|doi=10.1002/14356007.a23_583.pub3|display-authors=3}}</ref> Quartz is the only polymorph of silica stable at the Earth's surface. Metastable occurrences of the high-pressure forms [[coesite]] and [[stishovite]] have been found around [[impact structure]]s and associated with [[eclogite]]s formed during [[ultra-high-pressure metamorphism]]. The high-temperature forms of [[tridymite]] and [[cristobalite]] are known from silica-rich [[volcanic rock]]s. In many parts of the world, silica is the major constituent of [[sand]].<ref>{{cite book|title=An Introduction to Forensic Geoscience|vauthors=Berslien E|publisher=Wiley & Sons|year=2012|isbn=9781405160544|pages=138}}</ref>

===Biology===
Even though it is poorly soluble, silica occurs in many plants such as [[rice]]. Plant materials with high silica [[phytolith]] content appear to be of importance to grazing animals, from chewing insects to [[ungulate]]s. Silica accelerates tooth wear, and high levels of silica in plants frequently eaten by insects may have developed as a defense mechanism against predation.<ref>{{cite journal|vauthors=Massey FP, Ennos AR, Hartley SE|year=2006|title=Silica in grasses as a defence against insect herbivores: Contrasting effects on folivores and a phloem feeder|journal=[[Journal of Animal Ecology|J. Anim. Ecol.]]|volume=75|issue=2|pages=595–603|doi=10.1111/j.1365-2656.2006.01082.x|pmid=16638012|doi-access=free|bibcode=2006JAnEc..75..595M }}</ref><ref>{{cite journal|vauthors=Keeping MG, Kvedaras OL|year=2008|title=Silicon as a plant defence against insect herbivory: Response to Massey, Ennos and Hartley|journal=[[Journal of Animal Ecology|J. Anim. Ecol.]]|volume=77|issue=3|pages=631–3|doi=10.1111/j.1365-2656.2008.01380.x|pmid=18341561|doi-access=free|bibcode=2008JAnEc..77..631K }}</ref>

Silica is also the primary component of [[rice husk ash]], which is used, for example, in filtration and as supplementary cementitious material (SCM) in [[cement]] and [[concrete]] manufacturing.<ref>{{Cite journal |last1=Zain |first1=M. F. M. |last2=Islam |first2=M. N. |last3=Mahmud |first3=F. |last4=Jamil |first4=M. |date=2011 |title=Production of rice husk ash for use in concrete as a supplementary cementitious material |url=https://www.sciencedirect.com/science/article/pii/S0950061810003703 |journal=Construction and Building Materials |series=Composite Materials and Adhesive Bonding Technology |volume=25 |issue=2 |pages=798–805 |doi=10.1016/j.conbuildmat.2010.07.003 |issn=0950-0618}}</ref>

[[Silicification]] in and by cells has been common in the biological world and it occurs in bacteria, protists, plants, and animals (invertebrates and vertebrates).<ref>{{Cite journal |last=Perry |first=Carole C. |date=2003 |title=Silicification: The Processes by Which Organisms Capture and Mineralize Silica |url=https://pubs.geoscienceworld.org/msa/rimg/article-abstract/54/1/291/87497/Silicification-The-Processes-by-Which-Organisms?redirectedFrom=fulltext |journal=Reviews in Mineralogy and Geochemistry |volume=1 |issue=54 |pages=291–327|doi=10.2113/0540291 |bibcode=2003RvMG...54..291P }}</ref>

Prominent examples include:
*[[Test (biology)|Tests]] or [[frustule]]s (i.e. shells) of [[diatom]]s, [[Radiolaria]], and [[testate amoebae]].<ref name=Fern/>
*Silica [[phytolith]]s in the cells of many plants<ref>{{cite encyclopedia|last=Radini |first=Anita |title=Archaeobotany: Plant Microfossils |date=2024 |encyclopedia=Encyclopedia of Archaeology |edition=Second |pages=698–707 |editor-last=Nikita |editor-first=Efthymia |url=https://www.sciencedirect.com/science/article/pii/B9780323907996001142 |access-date=2024-06-20 |place=Oxford |publisher=Academic Press |doi=10.1016/b978-0-323-90799-6.00114-2 |isbn=978-0-323-91856-5 |editor2-last=Rehren |editor2-first=Thilo}}</ref> including [[Equisetaceae]],<ref>{{Cite journal |last1=Neumann |first1=Mike |last2=Wagner |first2=Sandra |last3=Noske |first3=Robert |last4=Tiersch |first4=Brigitte |last5=Strauch |first5=Peter |date=2010 |title=Morphology and Structure of Biomorphous Silica Isolated from Equisetum hyemale and Equisetum telmateia |journal=Zeitschrift für Naturforschung B |language=en |volume=65 |issue=9 |pages=1113–1120 |doi=10.1515/znb-2010-0910 |issn=1865-7117|doi-access=free }}</ref> many grasses, and a wide range of [[dicotyledon]]s.<ref>{{Citation |last1=Tubaña |first1=Brenda Servaz |title=Silicon in Soils and Plants |date=2015 |work=Silicon and Plant Diseases |pages=7–51 |editor-last=Rodrigues |editor-first=Fabrício A. |url=https://link.springer.com/10.1007/978-3-319-22930-0_2 |access-date=2024-07-19 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-22930-0_2 |isbn=978-3-319-22929-4 |last2=Heckman |first2=Joseph Raymond |editor2-last=Datnoff |editor2-first=Lawrence E.}}</ref><ref>{{Cite journal |last1=Irzaman |first1=Irzaman |last2=Yustaeni |first2=Diah |last3=Aminullah |first3=Aminullah |last4=Irmansyah |first4=Irmansyah |last5=Yuliarto |first5=Brian |date=2021-04-19 |title=Purity, Morphological, and Electrical Characterization of Silicon Dioxide from Cogon Grass (Imperata cylindrica) Using Different Ashing Temperatures |url=https://ejchem.journals.ekb.eg/article_165191.html |journal=Egyptian Journal of Chemistry |volume=64 |issue=8 |language=en |pages=4143–4149 |doi=10.21608/ejchem.2019.15430.1962 |issn=2357-0245}}</ref>
*The [[Sponge spicule|spicules]] forming the skeleton of many [[sponge]]s.<ref>{{Cite journal |last1=Uriz |first1=MJ |last2=Turon |first2=Xavier |last3=Becerro |first3=Mikel A. |last4=Agell |first4=Gemma |date=2003 |title=Siliceous spicules and skeleton frameworks in sponges: Origin, diversity, ultrastructural patterns, and biological functions |url=https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/jemt.10395 |journal=Microscopy Research and Technique |language=en |volume=62 |issue=4 |pages=279–299 |doi=10.1002/jemt.10395 |pmid=14534903 |issn=1059-910X}}</ref>