physical geography

weathering notesRock Type & Rock CycleCharacteristics of Rocks: Mineral Composition, Physical PropertiesWeathering Processes: Physical, Chemical, BiologicalFactors Affecting WeatheringGranite LandformsLimestone Landforms

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rock typeIgneous Rock- formed by cooling and crystallization/solidification of magma- source: melting of rocks in hot, deep crust and upper mantle- intrusive (magma cools within existing rocks in Earth’s crust):

- coarse-grained: magma cools slowly and has sufficient time to form large mineral grains

- granite (only found in continental crust - forms when continental crust is heated to its melting temperature)

- gabbro/norite (dark colored minerals augite and olivine exceed 50%)- extrusive (magma solidifies on surface):

- fine-grained: magma cools rapidly, allowing insufficient time for large crystals to grow

- andesite (intermediate volcanic igneous rock)- basalt (same composition as gabbro, most common kind of extrusive

igneous rock, ocean crust)- minerals: quartz, feldspar (orthoclase, plagioclase), mica (muscovite, biotite),

hornblende, augite, olivine- felsic (light-colored) minerals- mafic (dark-colored) minerals

Sedimentary Rock- formed by chemical precipitation or by dewatering, compaction and

cementation of deposited mineral grains - source: weathering and erosion of rocks exposed at surface- stratification/bedding: arrangement of sedimentary particles in layers

- each stratum/bed is a distinct layer of sediment- top/bottom surface of bed is called a bedding plane: represents break in

deposition (ie. change in environment)- types of sediments:

- clastic (fragments of rock debris, from physical weathering): gravel, sand, silt, clay

- chemical (precipitates from solution in water): oolitic limestone- biogenic (fossilized remains of plants or animals): peat, coral limestone

- process:- compaction and dewatering: weight of accumulating sediment forces the

grains together, squeezing out any water present and reducing pore space- cementation: substances dissolved in water precipitate to form a cement

that binds the sediment grains together (e.g. quartz, iron, calcite)- e.g. limestone, sandstone, shale

Metamorphic Rock- formed by recrystallization- source: rocks under high temperature and/or pressure in deep crust and upper

mantle- heat source: Earth’s internal heat

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- rock can be heated by burial or by nearby igneous intrusion- burial accompanied by increase in pressure due to weight of overlying rock- lower-grade metamorphism: forms slaty cleavage

- newly forming minerals create foliation that tends to be parallel to the bedding planes of the sedimentary rock undergoing metamorphosis

- higher-grade metamorphism: schistosity- grain size increases- foliation in coarse-grained metamorphic rocks is called schistosity

- types of metamorphism:- dynamic: pressure/mechanical deformation- contact: recrystallization due to contact with hot magma- regional: both mechanical deformation and chemical recrystallization

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Shale (sedimentary rock) Slate (metamorphic rock)

Schist (metamorphic rock)Gneiss (metamorphic rock)

low-grade

metamorphism

metamorphismmedium-grade

high-grade

metamorphism

Limestone (sedimentary rock)

Marble (metamorphic rock)

Quartz Sandstone(sedimentary rock)

Quartzite(metamorphic rock)

quartz cemented by quartz

recrystallization of entire mass

rock cycle

Explaining the Rock Cycle- On the Earth’s surface, igneous, sedimentary and metamorphic rocks are

uplifted and exposed to weathering and erosion, yielding sediment. The sediment accumulates in basins, where deeply buried sediment layers are compacted, dewatered and cemented into sedimentary rock.

- Sedimentary rock, entering the deep environment of high pressures and temperatures, undergoes metamorphism and forms metamorphic rock. Similarly, when subjected to high heat and/or pressure, igneous rock also undergoes metamorphism into metamorphic rock.

- When any of the three rock types melt due to high heat below the Earth’s surface, they form magma. Magma rises, and upon reaching a higher level, magma cools and solidifies, becoming intrusive igneous rock. It may also emerge at the surface to form extrusive igneous rock.

- Hence, the cycle is completed.

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