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UVM GEOL 110 - Igneous Minerals

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Igneous MineralsVolcanic provincesSlide 3Hot spotsBasalt flowsPlutonsIntrusionsMagmaSlide 9Melt Composition + ‘freezing’ TBack to silicate structures:Slide 12Slide 13Mineral StructuresSlide 15Slide 16Slide 17Characterizing mineralsEquilibriumSalty Ice cube experimentIgneous MineralsIgneous MineralsWe will be discussing and working in lab with We will be discussing and working in lab with the major igneous minerals and common the major igneous minerals and common accessory mineralsaccessory mineralsWe will look at putting these minerals together We will look at putting these minerals together into rocks and ways to identify and characterize into rocks and ways to identify and characterize those rocksthose rocksGain a sense of what the minerals and the rocks Gain a sense of what the minerals and the rocks they form tell us about the earth…they form tell us about the earth…Volcanic provincesVolcanic provincesHot spotsHot spotsBasalt flowsBasalt flowsPlutonsPlutonsIntrusionsIntrusionsMagmaMagmaDifferntiate magma based on it’s chemical Differntiate magma based on it’s chemical composition composition  felsic vs. mafic felsic vs. maficMelt Composition + ‘freezing’ TMelt Composition + ‘freezing’ TLiquid magma freezes into crystals  the composition of what freezes first is governed by the melt’s compositionAnalogous to the composition of seawater ice  icebergs are composed of pure water; pure water freezes first, leaving the concentrated brine behindIn magmas  More silica = lower T; more Ca, Mg=higher TSilica polymerization also affected by T and how much Si there is!Back to silicate structures:Back to silicate structures:nesosilicatesnesosilicatesinosilicatesinosilicatestectosilicatestectosilicatesphyllosilicatesphyllosilicatescyclosilictaescyclosilictaessorosilicatessorosilicatesDiscontinous series – Structures change, harder to re-equilibrateContinuous Series  plag re-equilibrates quicker and if not is a continuum in composition rather than a change in mineral as T decreasesLiquid hotMAGMACa2+Na+Mg2+Fe2+Si4+Si4+Si4+O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-rockcoolingMg2+Fe2+Mg2+Mineral StructuresMineral StructuresSilicates are classified on the basis of Si-O polymerism Silicates are classified on the basis of Si-O polymerism [SiO[SiO44]]4-4- Isolated tetrahedra Isolated tetrahedra NesosilicatesNesosilicatesExamples: olivine garnetExamples: olivine garnet[Si[Si22OO77]]6-6- Paired tetrahedra Paired tetrahedra SorosilicatesSorosilicatesExamples: lawsoniteExamples: lawsoniten[SiOn[SiO33]]2-2- n = 3, 4, 6 Ring silicates n = 3, 4, 6 Ring silicates CyclosilicatesCyclosilicatesExamples: benitoite BaTi[SiExamples: benitoite BaTi[Si33OO99]] axinite Caaxinite Ca33AlAl22BOBO33[Si[Si44OO1212]OH]OH beryl Beberyl Be33AlAl22[Si[Si66OO1818]]Mineral StructuresMineral StructuresChain Silicates – single and doubleChain Silicates – single and double[SiO[SiO33]]2-2- single chains single chains Inosilicates Inosilicates [Si[Si44OO1111]]4-4- Double tetrahedra Double tetrahedrapryoxenes pyroxenoidspryoxenes pyroxenoids amphiboles amphibolesMineral StructuresMineral StructuresSheet Silicates – aka PhyllosilicatesSheet Silicates – aka Phyllosilicates[Si[Si22OO55]]2-2- Sheets of tetrahedra Sheets of tetrahedra PhyllosilicatesPhyllosilicatesmicas talc clay minerals serpentinemicas talc clay minerals serpentineMineral StructuresMineral StructuresFramework silicates – aka TectosilicatesFramework silicates – aka Tectosilicates[SiO[SiO22] 3-D frameworks of tetrahedra: fully polymerized ] 3-D frameworks of tetrahedra: fully polymerized TectosilicatesTectosilicatesquartz feldspars feldspathoids zeolitesquartz feldspars feldspathoids zeoliteslow-quartzlow-quartzCharacterizing mineralsCharacterizing mineralsWITHIN classes (like the silicate classes) Minerals WITHIN classes (like the silicate classes) Minerals put into put into groupsgroups based on similar crystal structures based on similar crystal structures differing typically in chemical substitutiondiffering typically in chemical substitutionGroups usually named after principle mineralGroups usually named after principle mineralFeldspar group, mica group, feldspathoid groupFeldspar group, mica group, feldspathoid groupSitesSites – designated M1, M2, etc. – designate spots – designated M1, M2, etc. – designate spots where cations go into structurewhere cations go into structuredifferent site designations have different characteristics different site designations have different characteristics (‘see’ different charge, have different sizes, etc.) and (‘see’ different charge, have different sizes, etc.) and accommodate different ions based on thisaccommodate different ions based on thisEquilibriumEquilibriumNeed a description of a Need a description of a mineral’s equilibrium mineral’s equilibrium with it’s surroundingswith it’s surroundingsFor igneous minerals, this For igneous minerals, this equilibrium is with the equilibrium is with the melt (magma) it forms melt (magma) it forms from or is a representation from or is a representation of the Temperature and of the Temperature and Pressure of formationPressure of formationSalty Ice cube experimentSalty Ice cube experimentThought experiment: Put pure H2O ice cube Thought experiment: Put pure H2O ice cube into salty water, let it sit for a certain time and into salty water, let it sit for a certain time and look at the distribution of salt inside the ice look at the distribution of salt inside the ice cubecubeWhen the ice cube reaches a point where the When the ice cube reaches a point where the concentration of salt is the same through the concentration of salt is the same through the whole ice cube it has reached equilibiumwhole ice cube it has reached


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