Chapter 4: Geosphere Materials
Chapter 4: Geosphere Materials GEOL 1005
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This 5 page Class Notes was uploaded by Kerrigan Unter on Monday October 19, 2015. The Class Notes belongs to GEOL 1005 at George Washington University taught by Brown, C in Summer 2015. Since its upload, it has received 51 views. For similar materials see Environmental Geology in Geology at George Washington University.
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Date Created: 10/19/15
GEOL 1005 Chapter 4 Geosphere Materials 41 The Geosphere s Chemical Composition Element a substance that can t be broken down chemically into other substance Atom smallest possible division of an element made up of a nucleus containing neutrons and positively charged protons and negatively charged electrons number of neutrons can vary but the number of protons is distinctive Eight elements make up 98 of the geosphere s mass Fe O Si and Mg accounts for 91 The core is mostly iron and the mantle is a mixture of oxygen silicon magnesium and iron Oceanic crust is largely underwater 99 of both the oceanic crust and continental crust are made up of silicon oxygen iron and magnesium The combined percentage of iron and magnesium I the oceanic crust 127 is about 60 greater than that in the continental crust 80 The percentage of calcium in oceanic crust 82 is nearly twice that in the continental crust 46 The percentage of potassium in continental crust 15 is 15 ties that in the oceanic crust 0 1 The percentage of silicon in continental crust 283 is 20 greater than that in the oceanic crust 236 42 M inerals Where Elements Reside Minerals natural occurring inorganic solids made up of an element or a combination of elements that has an ordered arrangement of atoms and a characteristic chemical composition Ionic bonding positively charges ions attract negatively charges ions to from neutral combinations Covalent bonding neutral atoms combining and sharing electrons Chemical compounds attraction between ions forms bonds that hold atoms closely together Crystal orderly threedimensional arrangement that develops as ions and molecules combine Crystal structure solid atomic arrangement Crystallization the process of combining elements to form a crystal structure Planar twodimensional smooth surface Rockforming minerals quartz feldspars and ferromagnesian minerals Quartz SiOz Silica Hardness 7 Wellformed planar surface Broken quartz crystals have conchoidal curved surfaces Grains individual quartz crystals Very fine particles of quartz are dangerous to breathe Tetrahedron pyramidlike shape Color luster hardness crystal structure fracture density Feldspars Silicate minerals that contain silica aluminum potassium sodium and calcium Potassium feldspar Plagioclase feldspar Hardness 6 Light colored Tabular prismatic crystals that break apart along smooth planes Cleavage weal plane in a mineral s internal structure along which it will break Chemical weathering mineral changes at surface that involve chemical reactions Hydrolysis the reaction of water with minerals to form new minerals that have water in their atomic structure Clay product of feldspar chemical weathering Hydrothermal uids waterrich uids Hydrothermal alteration the mineral changes that hydrothermal uids cause Mica produces through feldspar hydrolysis at higher temperatures light colored mineral with a strongly layered atomic structure Muscovite in the most common lightcolored mica Ferromagnesian Minerals silicate minerals that contain iron and magnesium in their structures Olivine dark greenish grey crystals Hardness 7 Pyroxenes darkcolored dense short and rectangular crystals two poorly developed cleavages Form at high temperatures and pressures Serpentine minerals divine and pyroxene undergo chemical weathering anf hydrolyze Biotite mica mineral that contains iron and magnesium Amphibole elongate prismatic crystals that parallel pyroxenes in composition except for water in their atomic structure hornblende tremolite Sulfides combine elements and metals with sulfur galena sphalerite pyrite Oxide minerals elements that combine directly with oxygen rutile cassiterite magnetite hematite goethite Oxidation positive ions in minerals combine with oxygen chemical weathering process Carbonate minerals positively charged ions combine with negatively charged carbonate minerals calcite dolomite Precipitate when the concentration of calcium and carbonate ions in water is high enough they fall out of the water to form a solid Chemical sediment precipitated minerals Limestone accumulations of calcite on the sea oor becomes rock Carbonate minerals are prone to easily dissolve in acid Sinkholes produces by dissolution 43 Rocks Where Mineral Reside Rock combination of one or more minerals Igneous rock rocks that form from magma felsic composition or mafic composition Gabbro crystallizes from mafic magma in the crust Continental crust is more diverse compositionally than oceanic crust Andesite erupted subductionrelated magma Differentiation the composition of magma changes through the physical separation of early crystallized minerals Rock cycle dynamic plat tectonic processes can greatly alter rocks in a sequence of changes Volcanic igneous rocks rocks that form from lava Plutonic igneous rocks crystallize within the crust Crustal melting can occur Where the crust becomes thick or When heat is added Crustal melting produces different types of magma Outcrop surface exposure of the solid geosphere Joints fractures in massive rock along the Earth s surface Weathering set of physical and chemical processes that change rocks at Earth s surface Physical Weathering breaks rocks into smaller and smaller pieces Erosion the transportation of the geosphere materials from one place to another by natural movements of water Wind and ice Moraines bodies of rock debris carried and deposited by glaciers Bedload debris rolled and bounces along the bottoms of a stream channel Sediment rock and mineral grains transported by streams Clastic sediment sediment moved by Wind and water ranges in size from tiny clay particles to rock fragments as big as boulders Sedimentation depositing sediment Sedimentary Basins large areas Where sediment accumulates Beds basins Where sediments accumulate layer after layer Lithified a compaction progresses the sediment changes from its lose unconsolidated state to become solid rock Sedimentary rocks formed When loose sediment I exposed to higher pressures and temperatures in deep parts of sedimentary basins and the resulting compaction and cementation Mudstone muddy sediment Clastic sedimentary rock rock formed from elastic sediment Evaporites rocks formed when mineral precipitate Where evaporation had increased their concentration of seawater Metamorphic rocks rocks changed at high temperature and pressure any rocks can become a metamorphic rock Foliation twodimensional sheeted structure in rocks schistosity Gneiss contains discontinuous layers of large minerals separated by finergrained schistose layers Metamorphic grade sequence of schists can become gneiss as they recrystallize at higher and higher temperatures and pressures Marble metamorphosed limestone 44 Using Rocks Aggregate rock material used for construction sand gravel or crushed or broken stone Environmental concerns of aggregate mining Physical disturbances produces by quarrying Dust and noise Congestion and safety concerns
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