Download 4 - Earth materials

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:
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–  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:
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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.