MagmaMelt Composition + ‘freezing’ TSlide 3Slide 4Silicate structures:Mineral StructuresSlide 7Slide 8Slide 9Characterizing mineralsTectosilicatesEquilibriumNASA News 03-15-06Melt-crystal equilibrium 1Slide 15Melt-crystal equilibrium 1bWhy aren’t all feldspars zoned?Melt-crystal equilibrium 2 - miscibilitySlide 19MagmaMagmaDifferentiate magma based on it’s chemical Differentiate 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!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+Silicate structures:Silicate structures:nesosilicatesnesosilicatesinosilicatesinosilicatestectosilicatestectosilicatesphyllosilicatesphyllosilicatescyclosilictaescyclosilictaessorosilicatessorosilicatesMineral 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 thisTectosilicatesTectosilicatesFeldsparsFeldsparsAlbite: Albite: NaNaAlAlSiSi33OO88Substitute two Substitute two AlAl3+3+ for Si for Si4+4+ allows Caallows Ca2+2+ to be to be addedaddedAlbite-AnorthiteAlbite-AnorthiteSubstitute AlSubstitute Al3+3+ for Sifor Si4+4+ allows allows NaNa++ or K or K++ to be to be addedaddedAlbite-OrthoclaseAlbite-OrthoclaseEquilibriumEquilibrium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 formationNASA News 03-15-06NASA News 03-15-06Scientists say the minerals found in Stardust aerogels include magnesium olivine (forsterite)"In the coldest part of the solar system, we have found samples that have formed at extremely high temperatures. So, the hottest samples in the coldest place."Melt-crystal equilibrium 1Melt-crystal equilibrium 1When crystal comes out When crystal comes out of melt, some ions go in of melt, some ions go in easier easier  more Ca rich more Ca rich crystals form 1crystals form 1ststPrecipitated crystals react Precipitated crystals react with cooling liquid, with cooling liquid, eventually will re-eventually will re-equilibrate back, totallly equilibrate back, totallly cooled magma xstals cooled magma xstals show same compositionshow same compositionMagma at composition X Magma at composition X (30% Ca, 70% Na) cools (30% Ca, 70% Na) cools  first xstal bytownite first xstal bytowniteXXliquidusliquidussolidussolidusMelt-crystal equilibrium 1Melt-crystal equilibrium 1Magma at composition Magma at composition X (30% Ca, 70% Na) X (30% Ca, 70% Na) cools cools  first crystal first crystal bytownite (73% Ca, bytownite (73% Ca, 27% Na)27% Na)This shifts the This shifts the composition of the composition of the remaining melt such that remaining melt such that it is more Na-rich (Y)it is more Na-rich (Y)What would be the next What