Sedimentary Rock
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A sedimentary rock is one made up of particles of minerals that have settled out of water or wind in layers that have been subsequently lithified. Think of mud settling at the bottom of a lake, this is a sedimentary deposit.
How Sedimentary rocks form:
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As the sediments become buried under other sediment layers, pressures and temperatures increase. The sediment hardens into a sedimentary rock, or lithifies, after it has gone through the stages of compaction, dewatering, and cementation. During compaction, the grains of sediment are packed more tightly together. With increasing pressure some of the water between the sediment particles is squeezed out, dewatering the sediment. This process reduces the pore space, or open spaces between the grains. At this point, pressure and temperature conditions are such that certain minerals, usually calcite or quartz, fill some or all of the pore spaces and adhere to the sediment fragments, cementing them into a sedimentary rock.
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4 types of Sedimentary rocks:
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Chert- is a microcrystalline or cryptocrystalline sedimentary rock material composed of silicon dioxide (SiO2). It occurs as nodules and concretionary masses and less frequently as a layered deposit. It breaks with a conchoidal fracture, often producing very sharp edges. Early people took advantage of how chert breaks and used it to fashion cutting tools and weapons
Coal-is an organic sedimentary rock that forms mainly from plant debris. The plant debris usually accumulates in a swamp environment. Coal is combustible and is often mined for use as a fuel.
Shale-is a clastic sedimentary rock that is made up of clay-size (less than 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces.
Sandstone-is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering debris. Environments where large amounts of sand can accumulate include beaches, deserts, floodplains and deltas.
Coal-is an organic sedimentary rock that forms mainly from plant debris. The plant debris usually accumulates in a swamp environment. Coal is combustible and is often mined for use as a fuel.
Shale-is a clastic sedimentary rock that is made up of clay-size (less than 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces.
Sandstone-is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering debris. Environments where large amounts of sand can accumulate include beaches, deserts, floodplains and deltas.
Links:http://geology.com/rocks/sedimentary-rocks.shtml
http://www.rocksandminerals4u.com/sedimentary.html
http://www.rocksandminerals4u.com/sedimentary.html
Uses of Sedimentary rock
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Geologists use their understanding of sedimentary rock to do more than reconstruct the history of the Earth's surface. Most of the economically valuable resources that are extracted from the Earth's crust come from sedimentary rock. Most people know that sedimentary rocks are the source of fossil fuels, such as oil, natural gas, and coal, but the economic value of sedimentary rock influences almost every part of our lives.