Editing Ice crystal (section)

== Formation ==
[[File:Hexagonal Ice Crystals.svg|thumb|An example of a hexagonal plate (top) and a hexagonal column (bottom), typical ice crystal shapes.]]
 At ambient temperature and pressure, [[Properties of water|water molecules]] have a V shape. The two [[hydrogen]] atoms bond to the [[oxygen]] atom at a 105° angle.<ref name=":3">{{Cite web |last=Puiu |first=Tibi |date=2015-03-27 |title=Sandwiching water between graphene makes square ice crystals at room temperature |url=https://www.zmescience.com/science/chemistry/graphene-square-ice-0534534/ |access-date=2023-03-30 |website=ZME Science |language=en-US}}</ref> Ice crystals have a hexagonal [[Crystal structure|crystal lattice]], meaning the water molecules arrange themselves into layered [[Hexagon|hexagons]] upon freezing.<ref name=":0" />

Slower crystal growth from colder and drier atmospheres produces more hexagonal symmetry.<ref name=":1" /> Depending on environmental [[temperature]] and [[humidity]], ice crystals can develop from the initial hexagonal prism into many symmetric shapes.<ref>{{Cite book |last=Visconti |first=Guido |url=https://www.worldcat.org/oclc/46320998 |title=Fundamentals of physics and chemistry of the atmosphere |date=2001 |publisher=Springer |isbn=3-540-67420-9 |location=Berlin |oclc=46320998}}</ref> Possible shapes for ice crystals are columns, [[Needle ice|needles]], plates and [[Dendrite (crystal)|dendrites]]. Mixed patterns are also possible.<ref name=":0" /> The symmetric shapes are due to [[Deposition (chemistry)|depositional]] [[Crystal growth|growth]], which is when ice forms directly from water vapor in the atmosphere.<ref>{{Cite web |title=Sublimation and deposition - Energy Education |url=https://energyeducation.ca/encyclopedia/Sublimation_and_deposition#:~:text=An%20example%20of%20deposition%20is,as%20the%20formation%20of%20frost. |access-date=2023-04-10 |website=energyeducation.ca}}</ref> Small spaces in atmospheric [[Dust|particles]] can also collect water, freeze, and form ice crystals.<ref>{{Cite web |last=Utah |first=University of |title=We've been thinking of how ice forms in cirrus clouds all wrong |url=https://phys.org/news/2019-04-weve-ice-cirrus-clouds-wrong.html |access-date=2023-03-30 |website=phys.org |language=en}}</ref><ref>{{Cite web |title=How ice crystals form in clouds |url=https://analyticalscience.wiley.com/do/10.1002/micro.2104/ |access-date=2023-03-29 |website=Wiley Analytical Science Magazine|doi=<!-- --> }}</ref> This is known as [[nucleation]].<ref>{{Cite web |last=UCL |date=2016-12-09 |title=Understanding how ice crystals form in clouds |url=https://www.ucl.ac.uk/news/2016/dec/understanding-how-ice-crystals-form-clouds |access-date=2023-04-10 |website=UCL News |language=en}}</ref> [[Snowflake|Snowflakes]] form when additional vapor freezes onto an existing ice crystal.<ref>{{Cite web |title=Growth Rates and Habits of Ice Crystals between −20° and −70°C - Google Search |url=https://www.google.com/search?q=Growth+Rates+and+Habits+of+Ice+Crystals+between+%E2%88%9220%C2%B0+and+%E2%88%9270%C2%B0C |access-date=2024-03-10 |website=www.google.com}}</ref><ref>{{Cite web |title=How do snowflakes form? Get the science behind snow |url=https://www.noaa.gov/stories/how-do-snowflakes-form-science-behind-snow |access-date=2023-03-30 |website=www.noaa.gov |date=19 December 2016 |language=en}}</ref>[[File:Снежинка на разноцветном фоне.JPG|thumb|Further freezing of water on an ice crystal produces [[Snowflake|snowflakes]].]]
=== Trigonal and cubic crystals ===
[[Supercooling|Supercooled]] water refers to water below its [[Melting point|freezing point]] that is still liquid.<ref>{{Cite web |date=2014-12-20 |title=Supercool Clouds |url=https://earthobservatory.nasa.gov/images/84916/supercool-clouds#:~:text=Supercooling%20may%20sound%20exotic,%20but,of%20about%20-15%20degrees%20C. |access-date=2023-04-10 |website=earthobservatory.nasa.gov |language=en}}</ref> Ice crystals formed from supercooled water have [[Stacking fault|stacking defects]] in their layered hexagons. This causes ice crystals to display [[trigonal]] or [[Ice Ic|cubic]] symmetry depending on the temperature. Trigonal or cubic crystals form in the upper atmosphere where supercooling occurs.<ref>{{Cite journal |last1=Murray |first1=Benjamin J. |last2=Salzmann |first2=Christoph G. |last3=Heymsfield |first3=Andrew J. |last4=Dobbie |first4=Steven |last5=Neely |first5=Ryan R. |last6=Cox |first6=Christopher J. |date=2015-09-01 |title=Trigonal Ice Crystals in Earth's Atmosphere |journal=Bulletin of the American Meteorological Society |language=EN |volume=96 |issue=9 |pages=1519–1531 |doi=10.1175/BAMS-D-13-00128.1 |bibcode=2015BAMS...96.1519M |s2cid=120907603 |issn=0003-0007|doi-access=free }}</ref><ref>{{Cite web |title=Cubic ice (ice Ic) structure |url=https://water.lsbu.ac.uk/water/cubic_ice.html |access-date=2023-04-10 |website=water.lsbu.ac.uk}}</ref>

=== Square crystals ===
Water can pass through [[Lamination|laminated]] sheets of [[Graphite oxide|graphene oxide]] unlike smaller molecules such as [[helium]]. When squeezed between two layers of [[graphene]], water forms square ice crystals at room temperature. Researchers believe high pressure and the [[van der Waals force]], an [[Force|attractive force]] present between all molecules, drives the formation. The material is a new crystalline phase of ice.<ref name=":3" /><ref>{{Cite journal |last1=Algara-Siller |first1=G. |last2=Lehtinen |first2=O. |last3=Wang |first3=F. C. |last4=Nair |first4=R. R. |last5=Kaiser |first5=U. |last6=Wu |first6=H. A. |last7=Geim |first7=A. K. |last8=Grigorieva |first8=I. V. |date=2015 |title=Square ice in graphene nanocapillaries |url=https://www.nature.com/articles/nature14295 |journal=Nature |language=en |volume=519 |issue=7544 |pages=443–445 |doi=10.1038/nature14295 |pmid=25810206 |arxiv=1412.7498 |bibcode=2015Natur.519..443A |s2cid=4462633 |issn=1476-4687}}</ref>