Editing Formation of rocks

{{short description|Process of rock formations}}
[[File:Two-parts stone nikogda takih ne videl vot.JPG|thumb|right|Stone]]
:''This article discusses how rocks are formed. There are also articles on physical [[rock formation]]s, rock layerings ([[stratum|strata]]), and the formal naming of [[geologic formation]]s.''

[[terrestrial planet|Terrestrial]] '''rocks are formed''' by three main mechanisms:
* [[Sedimentary rock]]s are formed through the gradual accumulation of [[sediment]]s: for example, sand on a beach or mud on a river bed. As the sediments are buried they get compacted as more and more material is deposited on top. Eventually the sediments will become so dense that they would  essentially form a [[rock (geology)|rock]]. This process is known as [[lithification]].
* [[Igneous rock]]s have [[crystal]]lised from a [[melt (geology)|melt]] or [[magma]]. The melt is made up of various components of pre-existing rocks which have been subjected to melting either at [[subduction zone]]s or within the [[Earth]]'s [[mantle (geology)|mantle]]. The melt is hot and so passes upward through cooler [[country rock (geology)|country rock]]. As it moves, it cools and various rock types will form through a process known as [[fractional crystallisation (geology)|fractional crystallisation]]. Igneous rocks can be seen at [[mid-ocean ridge]]s, areas of [[volcanic arc|island arc volcanism]] or in [[hotspot (geology)|intra-plate hotspots]].
* [[Metamorphic rock]]s once existed as igneous or sedimentary rocks, but have been subjected to varying degrees of pressure and heat within the Earth's crust. The processes involved will change the composition and fabric of the rock and their original nature is often hard to distinguish. Metamorphic rocks are typically found in areas of [[mountain formation|mountain building]].

Rock can also form in the absence of a substantial pressure gradient as material that condensed from a [[protoplanetary disk]], without ever undergoing any transformations in the interior of a large object such as a [[planet]] or [[natural satellite|moon]].  [[astrophysics|Astrophysicists]] classify this as a fourth type of rock:  '''primitive rock'''. This type is common in [[asteroid]]s and [[meteorite]]s.<ref name=lissauer2019/>{{rp|145}}

== Rock formation ==

=== 19th-century efforts to synthesize rocks === <!-- this section appears to be substantially from the 1911 edition of Encyclopedia Britanica -->

The [[Chemical synthesis|synthetic]] investigation of rocks proceeds by experimental work that attempts to reproduce different rock types and to elucidate their origins and structures. In many cases no experiment is necessary. Every stage in the origin of clays, sands and gravels can be seen in process around us, but where these have been converted into coherent shales, sandstone and conglomerates, and still more where they have experienced some degree of metamorphism, there are many obscure points about their history upon which experiment may yet throw light. Attempts have been made to reproduce igneous rocks, by fusion of mixtures of crushed minerals or of chemicals in specially contrived furnaces. The earliest researches of this sort are those of [[Barthélemy Faujas de Saint-Fond|Faujas St Fond]] and of [[Horace-Bénédict de Saussure|de Saussure]], but Sir [[Sir James Hall, 4th Baronet|James Hall]] really laid the foundations of this branch of petrology. He showed (1798) that the whinstones ([[diabase]]s) of Edinburgh were fusible and if rapidly cooled yielded black vitreous masses closely resembling natural pitchstones and [[obsidian]]s. If cooled more slowly they consolidated as crystalline rocks not unlike the whinstones themselves and containing [[olivine]], [[augite]] and [[feldspar]] (the essential minerals of these rocks).<ref name=EB1911>{{EB1911|wstitle=Petrology |volume=21 |pages=326–327 |inline=1 |first=John Smith |last=Flett}}</ref>

Many years later [[Gabriel Auguste Daubrée|Daubrée]], [[Achille Ernest Oscar Joseph Delesse|Delesse]] and others carried on similar experiments, but the first notable advance was made in 1878, when [[Ferdinand André Fouqué|Fouqué]] and [[Auguste Michel-Lévy|Lévy]] began their researches. They succeeded in producing such rocks as porphyrite, [[leucite]]-[[tephrite]], [[basalt]] and dolerite, and obtained also various structural modifications well known in igneous rocks, e.g. the [[porphyritic]] and the [[Poikilitic#Ophitic|ophitic]]. Incidentally, they showed that while many basic rocks (basalts, etc.) could be perfectly imitated in the laboratory, the acid rocks could not, and advanced the explanation that for the crystallization of the latter the gases never absent in natural rock magmas were indispensable mineralizing agents. It has subsequently been proved that steam, or such volatile substances as certain borates, molybdates, chlorides, fluorides, assist in the formation of [[orthoclase]], [[quartz]] and [[mica]] (the minerals of [[granite]]). Sir James Hall also made the first contribution to the experimental study of metamorphic rocks by converting [[chalk]] into [[marble]] by heating it in a closed gun-barrel, which prevented the escape of the [[carbonic acid]] at high temperatures. In 1901 [[Frank Dawson Adams|Adams]] and [[John Thomas Nicholson|Nicholson]] carried this a stage further by subjecting marble to great pressures in hydraulic presses and have shown how the foliated structures, frequent in natural marble may be produced artificially.<ref name=EB1911/>

== Extraterrestrial rock ==
Off-[[Earth]], rock can also form in the absence of a substantial pressure gradient as material that condensed from a [[protoplanetary disk]], without ever undergoing transformations in the interior of a large object such as [[planet]]s and [[Moon (generic)|moon]]s.  [[Astrophysics|Astrophysicists]] classify this as a fourth type of rock:  '''Primitive rock'''<!-- bolded per [[WP:MOSBOLD]], as a target of a redirect -->.<ref name=lissauer2019>{{Cite book |title=Fundamental Planetary Sciences : physics, chemistry, and habitability |last1=Lissauer|first1=Jack J. |last2=de Pater|first2=Imke |year=2019 |publisher=Cambridge University Press |pages=145, 287–308 |isbn=9781108411981 |location=New York, NY, USA }}</ref>  

Primitive rocks "have never been heated much, although some of their constituents may have been quite hot early in the history of our [[Solar System]]. Primitive rocks are common on the surfaces of many asteroids, and the majority of meteorites are primitive rocks."<ref name=lissauer2019/>{{rp|145}}

[[File:Widmanstätten pattern Staunton meteorite.jpg|thumb|Widmanstätten pattern in an iron-rich meteorite]]
An example of a primitive rock is the [[Achondrite|achondritic]] [[Iron–nickel clusters|iron-nickel]] [[octahedrite]] mineral seen in the [[Widmanstätten pattern]] that is found in a number of iron-rich [[meterorite|meteorite]]s.  Consisting of [[kamacite]] and [[taenite]] and formed under extremely slow cooling conditions—about 100 to 10,000&nbsp;°C/Myr, with total cooling times of 10 Myr or less—it will precipitate kamacite and grow kamacite plates along certain [[crystallographic planes]] in the taenite [[crystal lattice]].<ref name=goldstein2009>{{cite journal |title=Iron meteorites: Crystallization, thermal history, parent bodies, and origin |journal=Chemie der Erde - Geochemistry |volume=69 |issue=4 |pages=293–325 |doi=10.1016/j.chemer.2009.01.002 |year=2009 |last1=Goldstein|first1=J.I |last2=Scott|first2=E.R.D |last3=Chabot|first3=N.L |bibcode=2009ChEG...69..293G}}</ref>

== See also ==
{{div col|colwidth=30em}}
* {{annotated link|Chemical gardening}}
* [[List of individual rocks]]
* [[List of minerals]]
* [[List of rock types]]
* [[List of rocks on Mars]]
* [[Petrifaction]]
* [[Rock cycle]]
{{div col end}}

==References==
{{reflist}}

== External links==
* [http://sci-culture.com/advancedpoll/GCSE/rockformation.htm The rock forming process], on sci-culture.com
{{portal bar|Earth sciences|Geology}}

[[Category:Petrology]]