Editing Formation of rocks (section)

== 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>