Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
EarthMaterials GEOL115 AlexanderLusk • Mostrocksare aggregates,made upofdifferent typesofgrains. Zoomingin • ThesolidEarthis madeupalmost completelyof rock. Grains…andminerals • IndividualgrainsthatmakeuparockoFen haveasimplechemicalcomposiGonand crystallinestructure–inotherwords,theyare minerals Forexample,thepreviousgranite: quartz: CrystallineSiO2 bio,te: Partofthemicafamily orthoclase/plagioclase: Partofthefeldsparfamily hornblende: Partoftheamphibolefamily Whatisamineral? Mineralsare- (i)Inorganic (ii)naturallyoccurring substancesthathavea (iii)fixedchemicalcomposi,on, anda (iv)solid, (v)crystallinestructure Quartz:SiO2 Iscoalmineral?Isglassamineral? Backtothebasics:atoms Bohrmodelofatoms: • • • • – Protons(+),neutrons(0),andelectrons(-) – Protonsandneutronshangoutinthenucleus – Electrons(e-)resideinelectronshells(orbitals), surroundingthenucleus Nucleusofatom=neutrons+protons: – neutronsmassof1(amu)andchargeof0 – Protonsmassof1(amu)andchargeof+1 – Electron-1chargeandnegligiblemass Inaneutrallychargedatom,numberofprotons=numberof electrons: – Numberofprotons=atomicnumber – Numberofprotons+Numberofneutrons=atomic weight Ionsareatomsthatcarryacharge(i.e.theywanttogiveupor takee-): – CaGons=+charge – Anions=-charge Isotopesareatomsofthesameelementwithdiffering numbersofneutrons.i.e.thenumberofneutronsmayvary withinatomsofthesameelement.Someisotopesareunstable whichresultsinradioacGvity: ExampleCarbon: – C12has6protonsand6neutrons – C14has6protonsand8neutrons – (12&14aremassnumbers=#protons+neutrons) Atomicbonding Twomostimportanttypesofbonds: • Ionic–electrontransfer • Covalent–electronsharing Othertypesofbonds: • VanderWaals–weakchargesbetweenlayers • Metallic–freefloaGngelectrons Bonding-ionic • Atomsgiveupelectronstoformions • Goodconductors • Candissolve Example:Halite-NaCl(sodiumchloride) ions Halite Atomicstackingpadernresultsinacubiccrystalstructure. Bonding-covalent • Electronpairs“cohabitate”(sharedpairs) • Toohardtogiveupelectrons • Strongbonds Example:oxygen(O2) Silicateminerals • Silicatemineralsmakeupmostofourplanet, especiallythemantleandcrust • Silicatesareconstructedofvariousarrangementsof SiO4tetrahedra • Thetetrahedramaybelinkedintochains,sheets,or frameworks • Metalionsmaintainchargebalance Quartzismadeofsilicatetrahedralinkedtogetherviacovalentbondswheretheyshareoxygens. IncreasingSicontent Otherimportantsilicates Non-silicates • Oxides:caGonscombinewithO2- Hema6te-Fe2O3;Magne6te-Fe3O4 • Carbonates:combinewithCO32- Calcite,dolomite-CaCO3 • SulfidesandSulfates:S2-orSO42- Galena-PbS;Gypsum-CaSO4* 2H2O • Halides:Cl1- SodiumChloride-NaCl(salt) • Na,veElements:uncombinedor "naGve"state Gold-Au,Silver-Ag,Copper-Cu Eagle’sNestMine,PlacerCo.,California. Californiagoldrush Whatcontrolswhichminerals/crystals growandtheirresulGngcharacterisGcs? • ComposiGon(Whatelementsareavailable?). • EnvironmentalCondiGons(P,T,fluids). • InternalStructure: – Chargeofatoms/ions – Sizeofatoms – Packingofatoms – Bonding Polymorphs PolymorphshavethesamechemicalcomposiGonbut differentcrystalstructuresandarethereforedifferent minerals. Bothmineralsarepolymorphsofcarbon Polymorphs:Aluminosilicates(Al2SiO5) ElementdistribuGonintheearth Core:Fe,Ni±S&O;e.g.,metals Mantle:Si,O,Mg,Fe;e.g.olivine Crust: Element: Wt.%: Charge: Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium Allothers O Si Al Fe Ca Na K Mg 46% 28% 8% 5% ~4% ~3% ~3% ~2% ~1% -2 +4 +3 +2 +2 +1 +1 +2 ElementalsubsGtuGon Elementsoflikesizesand/orchargescansubsGtuteforoneanother. ElementalsubsGtuGon Corundum:Al2O3(aluminumoxide) TraceamountsofimpuriGeswillgivethe mineraldifferentcolors… • Crgivesareddish/pinkcolor=ruby • Fe/Tigivesabluecolor=bluesapphire MineralproperGes: • • • • • • Color* Hardness Crystalformandsymmetry Cleavage “Streak” Density Usingmineralstogetarock’shistory Garnetasataperecorder Green“island”:1Gagarnet growth. White:450Magarnetgrowth aFerearliergarnetcrackedup. Red:360Ma garnetgrowth. EveryGmethatAfricaandNorthAmericacollidedthisgarnetgrewandrecordedtheP-T condiGons. Andalusitereplacedby kyaniteandstaurolite. KyaniteisthehighP formofAndalusite. Kyaniteisbeing deformed.Thisrock recordsburialand deformaGonofthe rock.