What is Rock cycle?
[[File:Rock cycle nps.PNG|thumb|The Rock Cycle]] The '''rock cycle''' is how rocks of one kind change into rocks of another kind.<ref name=credo/> There are three main kinds of rocks: [[igneous rock]], [[metamorphic rock]], and [[sedimentary rock]]. Each of these rocks can change into the other kinds by physical processes: cooling, melting, heat, [[weathering]]/[[erosion]], compacting (squeezing tightly together), [[cementation|cementing]], and pressure.<ref>{{Cite web|title=Earth Floor: Cycles|url=http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html|access-date=2021-02-17|website=www.cotf.edu}}</ref> When heated deep under ground, rocks become [[magma]] (liquid rock). Above ground, it is called [[lava]]. [[Sediment]], the particles from rock erosion and weathering, is the basis for sedimentary rock of the future.<ref>Blatt, Harvey and Robert J. Tracy 1996. ''Petrology; igneous, sedimentary, and metamorphic. 2nd ed, Freeman. {{ISBN|0-7167-2438-3}}</ref> '''Igneous rock''' is hardened magma, which can happen above or below ground.<ref name=credo>{{cite web |url= http://www.credoreference.com/topic/rock_cycle |title=Rock Cycle (2010)|first= |last= |work=The Hutchinson unabridged encyclopedia with atlas and weather guide |year=2011 |accessdate=25 May 2011}}</ref> It can melt into magma, erode into sediment, or be pressed tightly together to become metamorphic. '''Metamorphic rock''' is igneous or sedimentary rock that has been heated and squeezed.<ref name=credo/> It can erode into sediment or melt into magma. It is formed under extreme pressure and temperature deep inside [[mountain chain]]s. '''Sedimentary rock''' is compacted sediments which can come from any of the other rocks,<ref name=credo/> plus remains of living things. It can erode back into sediment, or be pressurized into metamorphic rock and can be melted to magma, which forms igneous rocks. These processes can occur in different orders, and the cycle goes on forever. Earth has several processes for changing rocks. Wind and water can creat