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Transcript of Sedimentary Rocks
How they are Formed
How Fossils are Formed
Sedimentary rocks are formed when existing rocks are broken down into sediments with the forces of Weathering, Erosion, Deposition,Compaction and Cementation.
Weathering: The chemical or physical breakdown of rocks
Erosion: The weathering and removal of rocks such as wind, water, ice, gravity or acid.
Depostion: When the forces used to breakdown rocks drops sediments.
Compaction: The process that squeezes together sediment, like water or gravity.
Cementation: When dissolved minerals are deposited into tiny spaces among sediment.
Sedimentary rocks can be classified into two groups according to how they form:
weathered bits of rock compacted together. This is called clastic sedimentary rocks. (ex. quartz, clay minerals)
dissolved minerals in water precipitate. This is called chemical sedimentary rocks. (ex. limestone, rock salt, rock gypsum, chert, and flint)
Clastic sedimentary rocks: They are often classified by texture
Coarse: over 2mm thickness of sediment is coarse grade found in sediments such as gravel.
Medium: 1/16th to 2mm thickness is medium grade found in sediments such as sand.
Fine: 1/16th to less than 1/256th thickness is fine grade found in sediments like mud.
Chemical sedimentary rocks: They are often characterized by their composition
Calcite, CaCO3: limestone to chalk.
Quartz, SiO2: chert or flint.
Halite, NaCl: rock salt.
Altered Plant Fragments:Coal.
Fossils are formed when an organic life form dies and its body is quickly buried in sediments afterwords. Over time gravity and the continual deposit of sediments cause the sediments to replace the original bones. The result is a copy of the remains that were once there.