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the three main rock types: sedimentary, metamorphic, and igneous.

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+the three main rock types: sedimentary, metamorphic, and igneous.
-[[Image:Rockcycle.jpg|right|thumb|300px|A diagram of the ''rock cycle''. Legend: 1 = [[magma]]; 2 = [[crystallization]] (freezing of rock); 3 = [[igneous rocks]]; 4 = [[erosion]]; 5 = [[sedimentation]]; 6 = [[sediments]] & [[sedimentary rocks]]; 7 = [[tectonic burial]] & [[metamorphism]]; 8 = [[metamorphic rocks]]; 9 = [[melting]].]]The '''rock cycle''' is a fundamental concept in [[geology]] that describes the dynamic transitions through [[geologic time]] among the three main [[rock (geology)|rock]] types: [[sedimentary]], [[metamorphic rock|metamorphic]], and [[igneous]]. As the diagram to the right illustrates, each type of rock is altered or destroyed when it is forced out of its equilibrium conditions. An igneous rock such as [[basalt]] may break down and dissolve when exposed to the [[Earth's atmosphere|atmosphere]], or melt as it is [[subduction|subducted]] under a [[continent]]. Due to the driving forces of the rock cycle, [[plate tectonics]] and the [[water cycle]], rocks do not remain in equilibrium and are forced to change as they encounter new environments. The rock cycle is an illustration that explains how the 3 rock types are related to each other and how processes change from one type to another over time.
-==Historical development==
-The original concept of the ''rock cycle'' is usually attributed to [[James Hutton]], the eighteenth century ''father of geology''. The rock cycle was a part of Hutton's ''[[uniformitarianism]]'' and his famous quote: ''no vestige of a beginning, and no prospect of an end'', applied in particular to the rock cycle and the envisioned cyclical nature of geologic processes. This concept of a repetitive non-evolutionary rock cycle remained dominant until the plate tectonics revolution of the [[1960]]s. With the developing understanding of the driving ''engine'' of [[plate tectonics]], the rock cycle changed from endlessly repetitive to a gradually evolving process. The ''[[Wilson cycle]]'' (a plate tectonics based rock cycle) was developed by [[J. Tuzo Wilson]] during the 1960s and [[70s]].
-==The cycle==
-[[Image:Igneous structures.jpg|thumb|300px|Structures of Igneous Rock. Legend: A = [[magma chamber]] (batholith); B = [[dyke]]/dike; C = [[laccolith]]; D = [[pegmatite]]; E = [[sill]]; F = [[stratovolcano]]; '''processes''': 1 = newer intrusion cutting through older one; 2 = [[xenolith]] or roof pendant; 3 = contact metamorphism; 4 = uplift due to laccolith emplacement. ]]
-===Transition to igneous===
-When rocks are pushed deep under the [[Earth]]'s surface, they may melt into [[magma]]. If the conditions no longer exist for the magma to stay in its liquid state, it will cool and solidify into an igneous rock. A rock that cools within the Earth is called [[intrusive]] or plutonic and will cool very slowly, producing a coarse-grained texture. As a result of [[volcanic]] activity, magma (which is called Lava when it reaches Earth's surface) may cool very rapidly while being on Earth's surface exposed to the [[Earth's atmosphere|atmosphere]] and are called [[extrusive]] or volcanic rocks. These rocks are fine-grained and sometimes cool so rapidly that no crystals can form and result in a natural [[glass]], such as [[obsidian]]. Any of the three main types of rocks (Igneous, Sedimentary, and Metamorphic rocks) can melt into magma and cool into igneous rocks.
-====Post-volcanic changes====
-Rock masses of igneous origin have no sooner cooled than they begin to change.  The solids with which the magma is charged are slowly dissipated, lava flows often remain hot and steaming for many years.  These gases attack the components of the rock and deposit new minerals in cavities and fissures.  The [[zeolite]]s are largely of this origin.  Even before these "post-volcanic" processes have ceased, atmospheric decomposition or [[weathering]] begins as the [[mineral]] components of volcanic and igneous rocks are not stable under surface atmospheric conditions.  Rain, frost, [[carbonic acid]], oxygen and other agents operate continuously, and do not cease until the whole mass has crumbled down and most of its ingredients have been resolved into new products or carried away in aqueous solution.  In the classification of rocks these secondary changes are generally considered unessential: rocks are classified and described as if they were ideally fresh, though this is rarely the case in nature.
-====Secondary changes====
-Epigenitic change (secondary processes) may be arranged under a number of headings, each of which is typical of a group of rocks or rock-forming minerals, though usually more than one of these alterations will be found in progress in the same rock.  [[Silicification]], the replacement of the minerals by crystalline or crypto-crystalline silica, is most common in [[felsic]] rocks, such as [[rhyolite]], but is also found in serpentine, etc.  [[Kaolinization]] is the decomposition of the [[feldspar]]s, which are the most common minerals in igneous rocks, into [[kaolin]] (along with quartz and other [[clay minerals]]); it is best shown by [[granite]]s and [[syenite]]s.  [[Serpentinization]] is the alteration of [[olivine]] to [[serpentine]] (with [[magnetite]]); it is typical of [[peridotite]]s, but occurs in most of the [[mafic]] rocks.  In [[uralitization]] secondary [[hornblende]] replaces [[augite]]; this occurs very generally in [[diabase]]s; [[chloritization]] is the alteration of augite (biotite or hornblende) to [[Chlorite group|chlorite]], and is seen in many diabases, [[diorite]]s and [[greenstone]]s.  [[Epidosite|Epidotization]] occurs also in rocks of this group, and consists in the development of [[epidote]] from biotite, hornblende, augite or plagioclase feldspar.
-===Transition to metamorphic===
-[[Image:Rough diamond.jpg|right|thumb|200px|This [[diamond]] is a mineral from within an igneous or metamorphic rock that formed at high temperature and pressure.]]
-Rocks exposed to high temperatures and/or pressures can be changed physically or chemically to form a different rock, called metamorphic. Regional metamorphism refers to the effects on large masses of rocks over a wide area, typically associated with mountain building events within [[orogeny|orogenic belts]]. These rocks commonly exhibit distinct bands of differing mineralogy and colors, called [[Foliation (geology)|foliation]]. Another main type of metamorphism is caused when a body of rock comes into contact with an igneous intrusion that heats up this surrounding country rock. This ''contact metamorphism'' results in a rock that is altered and re-crystallized by the extreme heat of the magma and/or by the addition of fluids from the magma that add chemicals to the surrounding rock ([[metasomatism]]). Any pre-existing type of rock can be modified by the processes of metamorphism.
-===Transition to sedimentary===
-Rocks exposed to the [[Earth's atmosphere|atmosphere]] are variably unstable and subject to the processes of [[weathering]] and [[erosion]]. Weathering and erosion breaks the original rock down into smaller fragments and carries away dissolved material. This fragmented material accumulates and is buried by additional material. While an individual grain of sand is still a member of the class of rock it was formed from, a rock made up of such grains fused together is sedimentary. Sedimentary rocks can be formed from the [[lithification]] of these buried smaller fragments ([[clastic]] sedimentary rock), the accumulation and lithification of material generated by living [[organism]]s ([[biogenic]] sedimentary rock - [[fossil]]s), or lithification of chemically precipitated material from a mineral bearing solution due to [[evaporate|evaporation]] ([[precipitate]] sedimentary rock). Clastic rocks can be formed from fragments broken apart from larger rocks of any type, due to processes such as [[erosion]] or from organic material, like plant remains. Biogenic and precipitate rocks form from the deposition of [[mineral]]s from chemicals dissolved from all other rock types.
-==Forces that drive the rock cycle==
-===Plate tectonics===
-{{main|Plate Tectonics}}
-In 1967, J. Tuzo Wilson published an article in Nature describing the repeated opening and closing of ocean basins, in particular focusing on  the current [[Atlantic Ocean]] area. This concept, a part of the plate tectonics revolution, became known as the ''Wilson cycle''. The Wilson cycle has had profound effects on the modern interpretation of the rock cycle as Plate tectonics became recognized as the driving force for the rock cycle.
-====Spreading ridges====
-The ''start'' of the cycle can be placed at the [[mid-ocean ridge|mid-ocean divergent boundaries]] where new [[magma]] is produced by [[Earth's mantle|mantle]] upwelling and a shallow ''melting zone''. This ''new'' or ''juvenile'' [[basalt]]ic magma is the first phase of the igneous portion of the cycle. It should be noted that the least dense magma phases tend to be favored in eruptions. As the ridge ''spreads'' and the new rock is carried away from the ridge, the interaction of heated circulating [[seawater]] through crevices starts the initial ''retrograde'' metamorphism of the new rock.
-====Subduction zones====
-[[Image:JuandeFucasubduction.jpg|thumb|300px|The Juan de Fuca plate sinks below the North America plate at the [[Cascadia subduction zone]].]]
-{{main|Subduction}}
-The new basaltic [[oceanic crust]] eventually meets a [[subduction]] zone as it moves away from the spreading ridge. As this crust is pulled back into the mantle, the increasing pressure and temperature conditions cause a restructuring of the mineralogy of the rock, this metamorphism alters the rock to form [[eclogite]]. As the slab of basaltic crust and some included sediments are dragged deeper, water and other more [[Volatility (chemistry)|volatile]] materials are driven off and rise into the overlying wedge of rock above the subduction zone which is at a lower pressure. The lower pressure, high temperature, and now volatile rich material in this wedge melts and the resulting buoyant magma rises through the overlying rock to produce [[island arc]] or [[continental margin]] [[volcanism]]. This volcanism includes more silicic lavas the further from the edge of the island arc or continental margin, indicating a deeper source and a more differentiated magma.
-At times some of the metamorphosed downgoing slab may be thrust up or [[obduction|obducted]] onto the continental margin. These blocks of mantle [[peridotite]] and the metamorphic [[eclogite]]s are exposed as [[ophiolite]] complexes.
-The newly erupted volcanic material is subject to rapid erosion depending on the climate conditions. These sediments accumulate within the basins on either side of an island arc. As the sediments become more deeply buried lithification begins and sedimentary rock results.
-====Continental collision====
-On the closing phase of the classic Wilson cycle, two continental or smaller terranes meet at a convergent zone. As the two masses of [[continental crust]] meet, neither can be subducted as they are both ''low density'' silicic rock. As the two masses meet, tremendous compressional forces distort and modify the rocks involved. The result is regional metamorphism within the interior of the ensuing [[orogeny]] or mountain building event. As the two masses are compressed, folded and faulted into a mountain range by the continental collision the whole suite of pre-existing igneous, volcanic, sedimentary and earlier metamorphic rock units are subjected to this new metamorphic event.
-====Accelerated erosion====
-The high mountain ranges produced by continental collisions are immediately subjected to the forces of erosion. Erosion wears down the mountains and massive piles of sediment are developed in adjacent ocean margins, shallow seas, and as continental deposits. As these sediment piles are buried deeper they become lithified into sedimentary rock. The metamorphic, igneous, and sedimentary rocks of the mountains become the new piles of sediments in the adjoining basins and eventually become sedimentary rock.
-====An evolving process====
-The plate tectonics rock cycle is an evolutionary process. Magma generation, both in the spreading ridge environment and within the wedge above a subduction zone, favors the eruption of the more silicic and volatile rich fraction of the crustal or upper mantle material. This lower density material tends to stay within the crust and not be subducted back into the mantle. The magmatic aspects of plate tectonics tends to gradual segregation within or between the mantle and crust. As magma forms, the initial melt is composed of the more silicic phases that have a lower melting point. This leads to partial melting and further segregation of the [[lithosphere]]. In addition the silicic continental crust is relatively buoyant and is not normally subducted back into the mantle. So over time the continental masses grow larger and larger.
-===The role of water===
-{{main|Water cycle}}
-[[Image:YehliuTaiwan-HoneycombWeathering.jpg|right|250px|thumb|The surface pattern on this pedestal rock is honeycomb weathering, caused by salt crystallization. This example is at [[Yehliu]], [[Taiwan]].]]
-The presence of abundant [[water (molecule)|water]] on Earth is of great importance for the rock cycle. Most obvious perhaps are the water driven processes of [[weathering]] and [[erosion]]. Water in the form of precipitation and [[acid]]ic [[soil]] water and [[groundwater]] is quite effective at dissolving minerals and rocks, especially those igneous and metamorphic rocks and marine sedimentary rocks that are unstable under near surface and atmospheric conditions. The water carries away the [[ion]]s dissolved in solution and the broken down fragments that are the products of weathering. Running water carries vast amounts of sediment in rivers back to the ocean and inland basins. The accumulated and buried sediments are converted back into rock.
-A less obvious role of water is in the metamorphism processes that occur in fresh seafloor volcanic rocks as seawater, sometimes heated, flows through the fractures and crevices in the rock These processes, illustrated by [[serpentinite|serpentinization]], are an important part of the destruction of volcanic rock.
-The role of water and other volatiles in the melting of existing crustal rock in the wedge above a subduction zone is a most important part of the cycle. Along with water, the presence of [[carbon dioxide]] and other carbon compounds from abundant marine [[limestone]] within the sediments atop the downgoing slab is another source of melt inducing volatiles. This involves the [[carbon cycle]] as a part of the overall rock cycle.
-==References==
-<!-- ----------------------------------------------------------
-  See http://wiki.riteme.site/wiki/Wikipedia:Footnotes for a
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-  footnotes using the <ref>, </ref> and  <reference /> tags
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-<div class="references-small">
-<references />
-*{{cite book | author=Blatt, Harvey and Robert J. Tracy
-| title=Petrology; Igneous, Sedimentary, and Metamorphic, 2nd Ed.
-| publisher=W. H. Freeman
-| year=1996 | id=ISBN 0-7167-2438-3}}
-*Fichter, Lynn S., (2000), ''[http://csmres.jmu.edu/geollab/Fichter/Wilson/Wilson.html The Wilson Cycle and a Plate Tectonic Rock Cycle]'',  James Madison University, Department of Geology and Environmental Science. Retrieved 18 Aug. 2005.
-*{{cite book | author=Plummer, Charles; McGeary, David; Carlson, Diane
-| title=Physical Geology
-| publisher=Mc Graw Hill
-| year=2005 | id=ISBN 0-07-293353-4}}
-*{{1911|article=Petrology}}
-</div>
-==External links==
-*[http://rst.gsfc.nasa.gov/Sect2/Sect2_1a.html The Six Fundamental Concepts about the Earth's Geology - NASA]
-*[http://csmres.jmu.edu/geollab/Fichter/Wilson/Wilson.html Wilson cycle - a detailed Plate Tectonics rock cycle]
-*[http://www.chariho.k12.ri.us/curriculum/MISmart/ocean/rocksong.htm The Rock Cycle Song]
-*[http://www.acad.carleton.edu/curricular/GEOL/DaveSTELLA/Rock%20Cycle/rock_cycle.htm Modelling the rock cycle with STELLA]
-*[http://geowords.com/histbooknetscape/j23.htm Wilson cycle]
-*[http://csmres.jmu.edu/geollab/Fichter/Wilson/wilsoncircl.html A circular Wilson cycle?]
-[[Category:Petrology]]
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