<P> The rock cycle is a basic concept in geology that describes the time - consuming transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous . As the adjacent diagram illustrates, each of the types of rocks 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 atmosphere, or melt as it is 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 three rock types are related to each other, and how processes change from one type to another over time . This cyclical aspect makes rock change a geologic cycle and, on planets containing life, a biogeochemical cycle . </P> <P> The original concept of the rock cycle is usually attributed to James Hutton, from 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 1960s . 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 1950s and 1960s . </P> <P> 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 cools and solidifies into an igneous rock . A rock that cools within the Earth is called intrusive or plutonic and cools very slowly, producing a coarse - grained texture such as the rock granite . As a result of volcanic activity, magma (which is called lava when it reaches Earth's surface) may cool very rapidly while being on the Earth's surface exposed to the 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, however the most common fine grained rock would be known as basalt . Any of the three main types of rocks (igneous, sedimentary, and metamorphic rocks) can melt into magma and cool into igneous rocks . </P> <P> Epigenetic 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 is 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 feldspars, which are the most common minerals in igneous rocks, into kaolin (along with quartz and other clay minerals); it is best shown by granites and syenites . Serpentinization is the alteration of olivine to serpentine (with magnetite); it is typical of peridotites, but occurs in most of the mafic rocks . In uralitization, secondary hornblende replaces augite; chloritization is the alteration of augite (biotite or hornblende) to chlorite, and is seen in many diabases, diorites and greenstones . Epidotization occurs also in rocks of this group, and consists in the development of epidote from biotite, hornblende, augite or plagioclase feldspar . </P>

What part of the rock cycle occur deep in earth's crust
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