1Minerals and RocksChapter 20Emily and Megan Earth System Science• Interconnected• Rocks and minerals• Interior processes• Erosion and deposition• Water and airElements of Earth by weight• Made of atoms• Earth is mostly iron, by weightCrust Elements, by weight• Made of atoms•Earth is mostly iron, y,by weight•Surface is mostly oxygen, by weightMinerals• Naturally occurring• Not composed of ‘organic’ molecules• Crystalline solid• Specific chemical compositionCrystals• Halite crystals•NaClCrystals• Amethyst quartz•PyriteShape reflectsShape reflects internal arrangement of atoms• Rhodochrosite• AsbestosMineral Classification• Crust is mostly oxygen and silicon• Silicon always bonded to oxygento oxygen• ‘SILICATES’• 92% of minerals of crust2Silicate Minerals• Silica bonded to metals• Aluminum, sodium, potassium, calcium– Feldspar: Most abundant mineral–‘felsic minerals’felsic minerals– Pale, average density• Examples of felsic minerals– Feldspar– Quartz– Muscovite micaSilicate Minerals• Silica bonded to metals• Iron, magnesium– Ferromagnesian silicates: ‘ferromags’–Dark denser than felsic mineralsDark, denser than felsic minerals• Examples of ferromags– Amphibole– Pyroxene– Biotite mica– OlivineSilicate StructureHardness• Resistance to scratching• Compare to glass/steel, penny, fingernailBreaking minerals• Strength of bonds within crystals• CleavageSl ithk–Some planes with weak bonding– Break along theseBreaking minerals• Strength of bonds within crystals•FractureNl tf–No planar arrangement of weak bonds– Conchoidal or irregularNon-silicates• Carbonates– Calcite: CaCO3• Oxides–Fe2O3Fe3O4Fe2O3, Fe3O4– tin, chromium, uranium• Sulfides– Zinc, lead, mercury–Pyrite: FeS2• Native elements: Au, CuMinerals crystallize• From liquid (usually) or gas (occasionally)• Magma: molten rock• Watery solutionsCrystallization of Magma• Cools, atoms attracted to one another• Arrange in orderly crystalline structures• When very hot, low-silica forms• Cooler, greater amounts of silica in them• Composition of magma changes as crystallization proceeds3Crystallize from watery solutions• Change solubility by changing physical or chemical conditions in magmatic water left– pH, other ion contentTemperature pressure–Temperature, pressure• Chemical sedimentary rock– Carbonates: made by organisms, mostly– Increase concentration by evaporation: evaporites Rock Types• Igneous• Sedimentary• MetamorphicRock cycle diagramSedimentary rocks• Cover 2/3 of Earth’s surface• Record conditions at time of deposition• Include remains of organisms preserved filas fossilsSedimentary rocksSediment is derived from weatheringCarried by fluidFormed at Earth’s surfaceImportant to reconstruct much of Earth's historySedimentary rocks Features of sedimentary rocks• Strata, or beds (most characteristic)• Bedding planes separate strata May have important characteristics• Size, shape and distribution of grain sizes• Fossils Sedimentary rocksTwo main types • Rocks formed by deposition of sediment—ClasticRkf db iitti f t•Rocks formed by precipitation from water--Chemical(includes rocks formed by organisms)Clastic Sediment Grains• Particle loosened from pre-existing rock• Transported to place of deposition• Shape, size, and sorting of grains can tell btth i tfd itiabout the environment of depositionLithificationProcess of becoming stone• Burial and compaction• Precipitation of cement• Each reduces ‘pore space’4Cement• Brought in by water• Mineral material between grains• Fills in pore spaces• Commonly calcite, silica, and sometimes iron oxideBedding and bedding planes• http://www.birdandhike.com/Hike/General_Info/Glossary/Gloss4.htmTypes of Clastic Rocks• Shale (most abundant)• Sandstone• ConglomerateFossils• Traces or remains of prehistoric life • Are the most important inclusions • Help determine past environments • Used as time indicators • Used for matching rocks from different places Shale with plant fossilsShale• Composed of very fine grained sediment• Shows obvious tendency to split along planes (fissile)Ull•Usually gray• Most common type of sedimentary outcropSandstoneSandstone• Composed of sand-size particles– Between 1/16 mm and 2 mm diameter– Particles may be individual mineral grains or rock fragments– Quartz most common type of grain• Environments include•Beach, •river, •shallow sea, •sand dunesConglomerate5Conglomerate• Composed of particles larger than 2 mm• Usually particles are rock fragmentsClastic rocks • Shale is the most common one• Made from solid particles• Classified by particle size ChalkFossiliferous limestoneCoquina Close up of coquinaChemical rocksDirect mineral precipitation from water• Evaporites such as rock salt or gypsum• Microcrystalline quartz (precipitated quartz) known as chert, flint, jasper, opal q) ,,jp,por agate• Travertine (calcite) and sinter (silica) from hotspring depositsTravertine• http://njminerals.org/travertine.html• http://www.gonomad.com/destinations/0409/hot_springs_of_the_sierras.html• http://www.cis.nctu.edu.tw/~whtsai/World%20Highlights/New%20Side%20Show%20Webpages/imagepages/Turkey%202001---Travertine%20stones%20and%20water%20in%20Pamukale.htmlEvaporites• http://www.bonnevillehealeyclub.org/• http://www.img.uni-karlsruhe.de/925.php•http://wwwpitt edu/~cejones/GeoImages/1Mi• http://www.paintersflat.net/saltflat.html • http://www.nv.blm.gov/Winnemucca/blackrock/BRHR_Planning.htm•http://www.pitt.edu/ cejones/GeoImages/1Minerals/2SedimentaryMineralz/Gypsum.html• http://www.flickr.com/photos/snogun/191723596/6Rock salthttp://geomaps.wr.usgs.gov/sfgeo/geologic/stories/marin_sedimentary.html• http://www.mii.org/Minerals/photochert.htmlChert• http://homestake.sdsmt.edu/Photos/Surface_geology_photos.htmClassification of sedimentary rocksFeatures of sedimentary rocks• Porosity• PermeabilitySedimentary rocks Economic importance • Coal• Petroleum and natural gas • Precipitation of iron and aluminum • Deposition of gold and tin• Sand, gravel,
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