Metamorphic processes can also occur at the Earth’s surface due to meteorite impact events and pyrometamorphism taking place near burning coal seams ignited by lightning strikes. Metamorphism often produces apparent layering, or banding, because of the segregation of minerals into separate bands. The recrystallization that takes place does so essentially in the solid state, rather than by complete remelting, and can be aided by ductile deformation and the presence of interstitial fluids such as water. Metamorphic rocks are often formed by processes deep within the Earth that produce new minerals, textures, and crystal structures. The changes can be chemical (compositional) and physical (textural) in character. Metamorphic rocks are those formed by changes in preexisting rocks under the influence of high temperature, pressure, and chemically active solutions.
Layers may be distinguished by differences in colour, particle size, type of cement, or internal arrangement. Sedimentary rocks are generally stratified- i.e., they have layering. Most are deposited from the land surface to the bottoms of lakes, rivers, and oceans. Sedimentary rocks are those that are deposited and lithified (compacted and cemented together) at the Earth’s surface, with the assistance of running water, wind, ice, or living organisms.
Igneous rocks are subdivided into two categories: intrusive (emplaced in the crust), and extrusive (extruded onto the surface of the land or ocean bottom), in which case the cooling molten material is called lava. They originate from processes deep within the Earth-typically at depths of about 50 to 200 kilometres (30 to 120 miles)-in the mid- to lower-crust or in the upper mantle.
Since their constituent minerals are crystallized from molten material, igneous rocks are formed at high temperatures. Igneous rocks are those that solidify from magma, a molten mixture of rock-forming minerals and usually volatiles such as gases and steam. Learn how igneous, sedimentary, and metamorphic rock become one another in the rock cycle See all videos for this article SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.
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