Editing Formation of rocks (section)

{{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}}