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In geology, '''metamorphic''' rock is formed when existing rock formations are exposed to great heat, pressure or chemical interaction for an extended period. Because its elemental composition remains essentially the same, the type of metamorphic rock that forms will depend on the rock from which it was formed and the temperature to which it was exposed.<ref name=Cairncross>B. Cairncross - ''Field guide to rocks and minerals of Southern Africa'' 2004. ISBN 978-1-86872-985-2 p. 260-261</ref>

Metamorphic rock formations can often be found adjacent to [[intrusive igneous rock]], where the cooling magma that formed the intrusive rock heated rock that had already existed in the area.

==Examples==
* Some [[graphite]] formations formed from [[coal]], though this is unlikely to have happened on Mars. (Igneous and meteoric graphite should be present.)
* [[Marble]] forms from [[limestone]], though some limestones are from biological sources and unlikely to exist on Mars.
* [[Gneiss]] forms from [[granite]].

==References==
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[[Category:Geology]]