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GEOG 203 Midterm 2 Review.doc

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GEOG 203
Bruce Murphy

Midterm 2 ReviewLecture 1 Rock types mineralogy physical and chemical weatheringBiogeochemistry The movement of elements and chemical species between components of the environmentHuman ImpactsThe effect of human activities deforestation acid precipitation and accelerated rates of soil erosionProcesses includeGas exchanges with soils CO2 CH4 N2ONutrient cycling Ca Mg K N PWeathering and soil formationAtmosphereVegetationSoil organic mattersoil mineral matterbedrockImportant questions to answer in this sectionWhat is the composition of major rock types which form the parent material of soilsWhat are the processes of physical and chemical weatheringWhat are the important properties of soil and what controls themHow do soil profiles develop Controlled by climate parent material vegetation topography and time how do they vary in propertiesHow do soils erode Predicting rates of soil erosion causes effects and alternativesBiogeochemical cycling Human impact on biogeochemistry effects of forest removal and acid rainRock typesIgneous rocks composed of minerals from molten magmaIntrusive Igneous rock that cools slowly in the crust Formers a pluton a large batholith of rock that makes up certain mountain ranges Ex Sierra Nevada Idaho or coastal range BC Granite and Diorite are examples of intrusiveExtrusive Formed as a result of melting of the earths crust at the surface Glossier surface considering they cool much quicker than intrusive Examples include obsidian and volcanic lavaIgneous mineralsSedimentary Rocks composed of minerals from other rocks and minerals at nearsurface temperature and pressuresMetamorphic formed under high heat and pressure secondary processGood figure 115116 in book for rock cycleChemical composition of earths crustMainly Oxygen 466 and Silicon 277 Aluminum 81 Iron 50 Calcium 36 Sodium 28 Potassium 26 Magnesium 21Ca K Mg N P S are all important plant nutrientsRefer to slide that shows mineralogy of various minerals and their compositions Mainly Silicon and OxygenThe silicon tetrahedronSilicon and Oxygen form a tetrahedral structure 4 oxygen atoms and 1 silicon atom in the middle The overall charge of a silicon tetrahedron is 4This negative charge is shared with adjacent Si atoms or with positively charged atoms cations such as Fe2 Mg2 etc Within the mineral latticeOlivines All FeMg to absorb negative charge from silicon tetrahedronPyroxenes single chain50 SiOSiAmphiboles double chain625 SiOSiMicasheet 75 SiOSiQuartz3D crystalline structure all sharing SiOSiChart in notes is good referenceRelative size of major ions KCaNaFeMgAlSiIsomorphous no change in structure substitution Replacement of the central Si atom by Al as minerals form from molten magma Results in alumunosilicate mineralsThis results in theloss of one positive charge for each atom replaced becauseSi4Al3To balance the loss of positive charge a cation must be incorporated into the structure to provide the extra positive charge K Na Ca2 These are called feldsparsAlbite Na NaAlSi2O8Anorthite Ca Ca2Al2Si2O8Orthoclase K KAlSi2O8Mineral structure affects weathering ability based on the strength of bonding between element and oxygen in the mineral SiOSi is resistant AlOAl is weaker FeMgO and NaKCaO is most easily weathered Quartz is strongest to weathering pure OSiO bondingSedimentary RocksClastic composed of weathered and transported minerals mixed mineralogyConglomerate boulders Sandstone sand size Shale clay sizeChemical composed of new minerals formedin sedimentary in situundergroundenvironment
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