Editing Metastability (section)

===Condensed matter and macromolecules===
Metastable phases are common in condensed matter and crystallography. This is the case for [[anatase]], a metastable polymorph of [[titanium dioxide]], which despite commonly being the first phase to form in many synthesis processes due to its lower [[surface energy]], is always metastable, with [[rutile]] being the most stable phase at all temperatures and pressures.<ref>{{Cite journal |last1=Hanaor |first1=Dorian A. H. |last2=Sorrell |first2=Charles C. |date=2011-02-01 |title=Review of the anatase to rutile phase transformation |journal=Journal of Materials Science |language=en |volume=46 |issue=4 |pages=855–874 |doi=10.1007/s10853-010-5113-0 |bibcode=2011JMatS..46..855H |s2cid=97190202 |issn=1573-4803|doi-access=free }}</ref>
As another example, [[diamond]] is a stable phase only at very high pressures, but is a metastable form of carbon at [[standard temperature and pressure]]. It can be converted to [[graphite]] (plus leftover kinetic energy), but only after overcoming an [[activation energy]] – an intervening hill. [[Martensite]] is a metastable phase used to control the hardness of most steel. Metastable [[polymorphism (materials science)|polymorphs]] of [[quartz|silica]] are commonly observed. In some cases, such as in the [[allotropes]] of solid [[boron]], acquiring a sample of the stable phase is difficult.<ref>{{cite journal|author=van Setten|last2=Uijttewaal|last3=de Wijs|last4=de Groot|journal=Journal of the American Chemical Society|volume=129|issue=9|pages=2458–2465|year=2007|title=Thermodynamic stability of boron: the role of defects and zero point motion|doi=10.1021/ja0631246|pmid=17295480|s2cid=961904|url=https://pure.rug.nl/ws/files/2796591/2007JAmChemSocvSetten.pdf|access-date=2019-07-08|archive-date=2021-04-15|archive-url=https://web.archive.org/web/20210415015024/https://pure.rug.nl/ws/files/2796591/2007JAmChemSocvSetten.pdf|url-status=dead}}</ref>

The bonds between the building blocks of [[polymer]]s such as [[DNA]], [[RNA]], and [[protein]]s are also metastable. [[Adenosine triphosphate]] (ATP) is a highly metastable molecule, colloquially described as being "full of energy" that can be used in many ways in biology.<ref>{{cite book|last1=Haldane|first1=J. B. S.|editor1-last=D. R.|editor1-first=Bates|title=The Planet Earth|date=1964|publisher=Pergamon Press|location=Germany|isbn=1483135993|page=332|edition=2nd|chapter-url=https://books.google.com/books?id=GNc_DQAAQBAJ&pg=PA332|access-date=May 29, 2017|language=en|chapter=Eighteen: Genesis of Life|quote=This is a highly stable molecule. About 11,500 calories of free energy are liberated when it is hydrolized to phosphate and adenosine-diphosphate (ADP).}}</ref>

Generally speaking, [[emulsion]]s/[[colloid]]al systems and [[glass]]es are metastable. The metastability of silica glass, for example, is characterised by lifetimes on the order of 10<sup>98</sup> years<ref>M.I. Ojovan, W.E. Lee, S.N. Kalmykov. An introduction to nuclear waste immobilisation. Third edition, Elsevier, Amsterdam, p.323 (2019)</ref> (as compared with the lifetime of the universe, which is thought to be around {{val|1.3787e10}} years).<ref name="Planck 2018">{{cite journal |author=Planck Collaboration |year=2020 |title=Planck 2018 results. VI.&nbsp;Cosmological parameters |journal=Astronomy & Astrophysics |volume=641 |at=page&nbsp;A6 (see PDF page&nbsp;15, Table&nbsp;2: "Age/Gyr", last&nbsp;column) |doi=10.1051/0004-6361/201833910 |arxiv=1807.06209 |bibcode=2020A&A...641A...6P |doi-access=free |s2cid=119335614}}</ref>

[[Abelian sandpile model|Sandpile]]s are one system which can exhibit metastability if a steep slope or tunnel is present. [[Sand|Sand grain]]s form a pile due to [[friction]]. It is possible for an entire large sand pile to reach a point where it is stable, but the addition of a single grain causes large parts of it to collapse.

The [[avalanche]] is a well-known problem with large piles of snow and ice crystals on steep slopes. In dry conditions, snow slopes act similarly to sandpiles. An entire mountainside of snow can suddenly slide due to the presence of a skier, or even a loud noise or vibration.