Editing Intrusive rock (section)

{{Short description|Magmatic rock formed below the surface}}

[[File:Intrusive big.png|thumb|upright=1.5|[[QAPF diagram]] for the classification of plutonic rocks]]
[[Image:A Yool DevilsTower 04Sep03 exif.jpg|thumb|[[Devils Tower]], United States, an igneous ''intrusion'' exposed when the surrounding softer rock eroded away]]

'''Intrusive rock''' is formed when [[magma]] penetrates existing rock, crystallizes, and solidifies underground to form ''[[Igneous intrusion|intrusions]]'', such as [[batholith]]s, [[dike (geology)|dikes]], [[Sill (geology)|sills]], [[laccolith]]s, and [[volcanic neck]]s.<ref name="kids-fun-science.com">Intrusive Rocks: [http://www.kids-fun-science.com/intrusive-rocks.html Intrusive rocks], accessdate: March 27, 2017.</ref><ref name="geocases2.co.uk">Igneous intrusive rocks: [http://www.geocases2.co.uk/printable/rocks.htm Igneous intrusive rocks] {{Webarchive|url=https://web.archive.org/web/20180512145313/http://www.geocases2.co.uk/printable/rocks.htm |date=2018-05-12 }}, accessdate: March 27, 2017.</ref><ref name="britannica.com">Britannica.com: [https://www.britannica.com/science/intrusive-rock intrusive rock | geology | Britannica.com], accessdate: March 27, 2017.</ref>

Intrusion is one of the two ways [[igneous rock]] can form. The other is [[extrusive rock|extrusion]], such as a [[Types of volcanic eruptions|volcanic eruption]] or similar event. An intrusion is any body of intrusive igneous rock, formed from magma that cools and solidifies within the crust of the [[planet]]. In contrast, an ''extrusion'' consists of extrusive rock, formed above the surface of the crust.

Some geologists use the term '''plutonic rock''' synonymously with intrusive rock, but other geologists subdivide intrusive rock, by crystal size, into coarse-grained plutonic rock (typically formed deeper in the [[Earth's crust]] in batholiths or [[stock (geology)|stocks]]) and medium-grained [[Subvolcanic rock|subvolcanic or hypabyssal rock]] (typically formed higher in the crust in dikes and sills).<ref name="philpotts-ague-2009-53">{{cite book |last1=Philpotts |first1=Anthony R. |last2=Ague |first2=Jay J. |title=Principles of igneous and metamorphic petrology |date=2009 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=9780521880060 |page=52 |edition=2nd}}</ref>