Sedimentary+Rocks

Sedimentary Rocks Weathering and Erosion Sediments are small pieces of rock that are moved and deposited by water, wind, glaciers, Citification Compaction- Citification begins with compaction. The weight of overlying sediments forces the sediment grains closer together, causing physical changes. Cementation-cementation occurs when dissolved minerals precipitate out of groundwater and their growth glues sediment grains together n2 solid rock. Bedding- the primary feature of sedimentary rock is horizontal layering called bedding, which results from the way sediment settles out of water or wind. Bedding n which the particle sizes become progressively heavier and coarser toward the bottom layers is called graded bedding. Cross-bedding is formed as inclined layers of sediment r deposited across a horizontal surface. Sedimentary Features Ripple Marks- when sediment is moved n2 small ridges by wind or wave action or by a river current, ripple marks form. Visualizing cross- bedding and ripple marks- moving water and loose sediment result n the formation of sedimentary structures such as cross-bedding and ripple marks. Sorting and rounding- as sediment is transported, pieces that began w/an angular shape knock n2 each other and become rounded as their edges r broken off. Evidence of past life- fossils r the preserved remains, impressions, or any other evidence of once-living organisms. During citification, parts of an organism can b replaced by minerals and turned n2 rocks, such as shells that have been turned n2 stone. Elastic Sedimentary Rocks- the most common sedimentary rocks, clastic sedimentary rocks, r formed from the abundant deposits of loose sediments that accumulate on earth's surface. Clastic refers to rock and mineral fragments produced by weathering and erosion. These rocks r further classified according to the sizes of their particles. Clastic Sedimentary rocks Coarse-grained rocks- sedimentary rocks consisting of gravel-sized rock and mineral fragments r classified as coarse-grained rocks. Conglomerates have rounded gravel-sized particles. Breccias r composed of angular, gravel-sized particles. Medium-grained rocks- sedimentary rocks that contain sand-sized rock and mineral fragments r classified as medium grained clastic rocks. Porosity is the percentage of open spaces between grains n mineral, such ad rock. When open spaces between grains n a rock t connected to one another, fluids can move through porous rock such as sandstone. Sandstone layers can b valuable as underground reservoirs of oil, natural gas, and groundwater. Fine-grained rocks- sedimentary rocks consisting of silt-and clay-sized particles r called fine-grain rocks. Fine-grained sedimentary rock has low porosity and often forms barriers that hinder the movement of groundwater and oil. Chemical and Biochemical Sedimentary Rocks- the formation of chemical and biochemical rocks involves the processes of evaporation and precipitation of minerals. Chemical sedimentary rocks- when the concentration of dissolved minerals n a body of water reaches saturating, crystal grains precipitate out of solution and settle to the bottom. The resulting layers of chemical sedimentary rocks r called evaporate. The constant evaporation from a body of salt water results n precipitation of large amounts of salts. Biochemical sedimentary rocks- biochemical sedimentary rocks r formed from the remains of once-living organisms. The most abundant of dies type of rock is limestone, which is composed primarily of calcite. After the death of organisms that used calcium carbonate to make their shells, the shells settle to the bottom of the ocean and can form thick layers of carbonate sediment. During burial n lithification of the carbonate sediment formed from the shells of once-living organisms, calcium carbonated precipitates out of the water, crystallizes between the grains of carbonate sediment, and forms limestone. Recognizing Metamorphic rock Metamorphic textures- Nonaffiliated metamorphic rocks r composed mainly of minerals that form w/blocky crystal shapes. Increasing grain size parallels changes n composition and development of foliation. Grain size is not a factor in nonaffiliated rocks. Grades of metamorphism- different combinations of temp. And pressure result n different grades of metamorphism. Each of the grades-low, intermediate, and high-is associated w/a diff. suite of minerals and textures. Metamorphism of shale results n the formation of minerals that provide the wide variety of color observed n slate. Types of Metamorphism Regional Metamorphism- when high temp. And pressure affect large regions of earths crust, dye produce large belts of regional metamorphism, ranging from low grade to high grade. Regional metamorphism results n changes n minerals and rock type, plus folding and deforming of the rock layers that make up the area. Contact Metamorphism-when molten material, such as that n an igneous intrusion, comes n contact w/ solid rock, a local effect called contact metamorphism occurs. High temp. And moderate-to-low pressure form mineral assemblages that r characteristic of contact metamorphism. Hydrothermal metamorphism- when very hot water reacts w/rock and alters its chemical and mineral composition, hydrothermal metamorphism occurs. Chemical changes r common during contact metamorphism near igneous intrusion and active volcanoes. Economic Importance of Metamorphic rocks and minerals- many of the economic mineral resources that make the modern way of life possible r produced by metamorphic processes. Metallic mineral resources- although deposits of pure metals r occasionally discovered, many metallic deposits r precipitated from hydrothermal solutions. Nonmetallic mineral resources- many nonmetallic resources r also produced by metamorphism, including talc, asbestos, and graphite. The rock cycle- the 3 types of rock r grouped according to how dye form. Igneous rock crystallizes from magma; sedimentary rocks form from cemented of precipitated sediments; and metamorphic rocks form from changes n temp. And pressure. Any rock can b changed n2 any other type of rock. This continuous changing and remaking of rock is called the rock cycle. The rock cycle shows some of the series of changes rocks undergo above and beneath earths surface.