The earth's crust is composed of many kinds of rocks, each of which is made up of one or more minerals. Rocks can be classified into three basic groups:
• igneous,
• sedimentary, and
• metamorphic.
In this section we will review these rock types in more detail as well as important internal and external processes in the rock cycle.
Igneous rocks
Igneous rocks are the most common rock type found in the earth's crust. They form when magma cools and crystallizes subsurface (intrusive igneous rocks) or lava cools and crystallizes on the surface (extrusive igneous rocks).
Granite is an example of an intrusive igneous rock, whereas basalt is an extrusive igneous rock.
Sedimentary rocks
Sedimentary rocks are formed by:
• the consolidation of the weathered fragments of pre-existing rocks,
• by the precipitation of minerals from solution, or
• by compaction of the remains of living organisms.
The processes involving weathered rock fragments include erosion and transport by wind, water or ice, followed by deposition as sediments.
Sedimentary rocks
As the sediments accumulate over time, those at the bottom are compacted. They are cemented by minerals precipitated from solution and become rocks. The process of compaction and cementation is known as lithification.
Some common types of sedimentary rocks are limestone, shale, and sandstone. Gypsum represents a sedimentary rock precipitated from solution. Fossil fuels such as coal and oil shale are sedimentary rocks formed from organic matter.
Metamorphic rocks
Metamorphic rocks are formed when solid igneous, sedimentary or metamorphic rocks change in response to elevated temperature and pressure and/or chemically active fluids. This alteration usually occurs subsurface.
Metamorphosis may involve a change in texture (recrystallization), a change in mineralogy or both. Marble is a metamorphosed form of limestone, while slate is transformed shale. Anthracite is a metamorphic form of coal.
The Rock Cycle
The rock cycle illustrates connections between the earth's internal and external processes and how the three basic rock groups are related to one another.
Internal processes include melting and metamorphism due to elevated temperature and pressure. Convective currents in the mantle keep the crust in constant motion (plate tectonics). Buried rocks are brought to the surface (uplift), and surface rocks and sediments are transported to the upper mantle region(subduction).
The Rock Cycle
Two important external processes in the rock cycle are weathering and erosion.
Weathering is the process by which rock materials are broken down into smaller pieces and/or chemically changed.
Once rock materials are broken down into smaller pieces, they can be transported elsewhere in a process called erosion. The main vehicle of erosion is moving water, but wind and glaciers can also erode rock.
The two important external processes in the rock cycle is call weathering and erosion.
Sedimentary rock production is a dynamic process, involving the accumulation of weathered particles to compensate for the denudation of land elsewhere. For example, in the southern coast of England, where white chalk cliffs are exposed to active wind and water erosion, large chunks of land regularly fall off after extensive weakening, causing coastal residences to be constantly reallocated. Some creationists (people who believe the earth is only 6,000 years old) say that the reduction of land by erosion could not have persisted for millions or billions of years because the continents would have been leveled by now. They calculate that in the 4.5 billion years geologists have assigned to earth's history, erosion could have reduced the continents to sea level as many as 340 times. This process is denudation, and it's estimated by geologists that the amount of sedimentary material continuously being dumped into the Atlantic Ocean by the Mississippi River represents a denudation rate that implies the continent of North America would be leveled in only 12 million years (still a far cry from the biblical timescale), far too short for current reconstructions of Geo-history. But geologists realize this argument ignores the dynamic nature of the rock cycling process. Material lost by denudation is compensated by sedimentary deposition and accumulation elsewhere. That, indeed, is a fundamental tenet of the geologist's principle of isostasy, without which the Flood's subsequent (postulated) tectonic upheavals could not have settled to the earth we now live in. Also, geologists recognize the argument for a young earth based on erosion rates is specious for another reason: namely, it ignores the process geologists used to call diastrophism. It is tectonic in nature and results in continents being uplifted at consistent rates over long periods of time, thus counterbalancing erosion. The Himalayan Mountains are being eroded, so creationists might argue that this orogenic belt could not be millions of years old or it would have been long since leveled by erosion. Actually, geologists observe that the mountains are being slowly uplifted by tectonic processes, so that erosion is not reducing its volume. Tectonic uplift is driven by radioactive elements in the continental crust. This major component of earth's geology is amply sufficient to prevent complete denudation of the continents and allow the landmasses of the lithosphere to persist for billions of years despite erosive forces acting on them constantly. Independent evidence, moreover, demonstrates that sea level was much higher relative to continental elevation for most of earth's history, so erosion wouldn't have been nearly as powerful an agent of topographical change as it is now: instead, deposition predominated, hence our remarkably rich rock record, spanning 3.7 billion years. Lastly, to turn the creationist's argument into an evolutionist one, erosion has leveled vast portions of uneven, irregular geology to a completely flat, erosional surface called a peneplain. This feature is evident at certain levels in the Grand Canyon and elsewhere and requires sustained operation of erosion for much more time than can be accommodated into a biblical, 6,000 year framework, much less a year-long Flood (which creationists use to explain the rock record).
There are a lot of sedimentary rocks along the rivers
here we studied three types of rocks and how they formed,we also studied about rocks cycle and its two important process due to which rock cycle take place
Entendido
Las rocas actualmente visibles en la superficie de la Tierra se han movido a través de etapas de transición que las transformaron de una forma en otra. La importancia del ciclo de las rocas está en cómo se forman y reciclan las distintas capas que componen la Tierra. De acuerdo con el Centro de Tecnologías de la Educación, estas transiciones ocurren cuando la roca se forma, se descompone y se vuelve a formar
How can we differentiate clearly igneous rocks from metamorphic rocks in the field?
existen diferentes tipos de rocas, como las rocas sedimentarias, entre otras, algunas se encuentran en la superficie y otras no ya que debido a su composición se encuentran en las capas inferiores de la tierra. el tipo de roca depende de muchos factores, como la composición, diferencia de temperaturas o ubicación, también debemos tener en cuenta la textura y minerales que contenga ya que pueden darle diversos usos para determinadas rocas.
según la ubicación de la roca gracias a las placas tectonicas estas pueden elevarse hasta la superficie o sedimentarse y caer por las grietas hasta las profundidades de la tierra.
The basic types of rocks are 3: Rocks igneous (formed by lava or margma solidified and compacted), sedimentary rocks (formed by the union of compacted segments) and metamorphic rocks (formed by the modification of the rocks due to high pressure and temperature). The rock cycle is given by the weathering and erosion where crustal rocks are subducted into the mantle, while internal arrive at the surface.