Feldspar GroupTectosilicatesFeldspar Group – Albite-Anorthite seriesSlide 4Staining techniqueFeldspar Group – Albite-Orthoclase seriesAlkali Feldspar ExsolutionAlkali Feldspar lamellaeFeldspathoid GroupFeldspathoids, Cont.Slide 11Slide 12Distinguishing Forsterite-FayaliteSlide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Pyroxene ChemistrySlide 34Orthopyroxene - ClinopyroxeneOrthopyroxene – Clinopyroxene solvus T dependenceSlide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Igneous MineralsFeldspar GroupFeldspar GroupMost abundant mineral in Most abundant mineral in the crust the crust  6 of 7 most 6 of 7 most common elementscommon elementsDefined through 3 end-Defined through 3 end-members members  Albite (Na), Anorthite (Ca), Albite (Na), Anorthite (Ca), Orthoclase (K)Orthoclase (K)Comprised of 2 series:Comprised of 2 series:Albite-anorthite (Na-Ca)Albite-anorthite (Na-Ca)Albite-orthoclase (Na-K)Albite-orthoclase (Na-K)TectosilicatesTectosilicatesFeldsparsFeldsparsAlbite: 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-OrthoclaseFeldspar Group – Albite-Anorthite seriesFeldspar Group – Albite-Anorthite seriesComplete solid solution Complete solid solution  Plagioclase FeldsparsPlagioclase Feldspars6 minerals6 mineralsAlbite (Na)Albite (Na)OligoclaseOligoclaseAndesineAndesineLabradoriteLabradoriteBytowniteBytowniteAnorthite (Ca)Anorthite (Ca)Albite-Anorthite double dutyAlbite-Anorthite double dutyEnd-members (Pure Na or Ca)End-members (Pure Na or Ca)Minerals 90-99.99% Na or CaMinerals 90-99.99% Na or CaNotation:Notation:AnAnxxAbAbyy  An An2020AbAb8080=Oligoclase=OligoclaseFeldspar Group – Albite-Anorthite seriesFeldspar Group – Albite-Anorthite seriesOptical techniques to Optical techniques to distinguish between distinguish between plagioclase feldspars:plagioclase feldspars:Michel-Levy Method – uses Michel-Levy Method – uses extinction angles of twinned extinction angles of twinned forms to determine An-Ab forms to determine An-Ab contentcontentCombined Carlsbad-Albite Combined Carlsbad-Albite Method Method  uses Michel- uses Michel-Levy technique for both Levy technique for both sides of a twin formsides of a twin formStaining techniqueStaining techniqueStains that attach Stains that attach to K really well to K really well (Like Co(NO3)2 ) (Like Co(NO3)2 ) will higlight the K-will higlight the K-feldspars quickly feldspars quickly and easily in hand and easily in hand specimen or thin specimen or thin sectionsectionFeldspar Group – Albite-Orthoclase seriesFeldspar Group – Albite-Orthoclase seriesHigh – T mineralsHigh – T mineralsSanidineSanidineAnorthoclaseAnorthoclaseMonalbiteMonalbiteHigh AlbiteHigh AlbiteLow Temperature Low Temperature exsolution at solvusexsolution at solvusChicken soup Chicken soup separationseparationForms 2 minerals, in igneous Forms 2 minerals, in igneous rocks these are typically rocks these are typically intergrowths, or exsolution intergrowths, or exsolution lamellae – perthitic texturelamellae – perthitic textureMiscibility Gapmicroclineorthoclasesanidineanorthoclasemonalbitehigh albitelow albiteintermediate albiteOrthoclaseKAlSi3O8AlbiteNaAlSi3O8% NaAlSi3O8Temperature (Temperature (ºC)ºC)3003009009007007005005001100110010109090707050503030Several minerals – Several minerals – Alkali FeldsparsAlkali FeldsparsAlkali Feldspar ExsolutionAlkali Feldspar ExsolutionMelt cools past solvus Melt cools past solvus (line defining (line defining miscibility gap)miscibility gap)Anorthoclase, that had Anorthoclase, that had formed (through formed (through liquidus/solidus) liquidus/solidus) separates (if cooling is separates (if cooling is slow enough) to form slow enough) to form orthoclase orthoclase andand low low albitealbiteIn hand sample – In hand sample – schiller effect schiller effect  play play of colors caused by of colors caused by lamellaelamellaeMiscibility Gapmicroclineorthoclasesanidineanorthoclasemonalbitehigh albitelow albiteintermediate albiteOrthoclaseKAlSi3O8AlbiteNaAlSi3O8% NaAlSi3O8Temperature (Temperature (ºC)ºC)3003009009007007005005001100110010109090707050503030LiquidAlkali Feldspar lamellaeAlkali Feldspar lamellaeFeldspathoid GroupFeldspathoid GroupVery similar to Very similar to feldspars and zeolitesfeldspars and zeolitesInclude Nepheline, Include Nepheline, Analcime, and LeuciteAnalcime, and LeuciteAlso framework Also framework silicates, but with silicates, but with another Al substitution another Al substitution for Sifor SiOnly occur in Only occur in undersaturated rocks undersaturated rocks (no free Quartz, Si-(no free Quartz, Si-poor) because they poor) because they react with SiOreact with SiO22 to form to form feldsparsfeldsparsFeldspathoids, Cont.Feldspathoids, Cont.NephelineNephelineImportant Important feldspathoid feldspathoid mineralmineralIndicates Indicates undersaturated undersaturated magmamagmaOlivine (001) view blue = M1 yellow = M2Olivine (001) view blue = M1 yellow = M2M1 in rows M1 in rows and share and share edgesedgesM2 form M2 form layers in a-c layers in a-c that share that share corners corners Some M2 and Some M2 and M1 share M1 share edgesedgesbbaaNesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedraOlivine – complete solid solution Olivine – complete solid solution Forsterite-Fayalite Forsterite-Fayalite  Fo FoxxFaFayyFayalite – Fe end-member Fayalite – Fe end-member Forsterite – Mg end-memberForsterite – Mg end-memberOlivine Occurrences:Olivine Occurrences:Principally in mafic and ultramafic igneous and meta-igneous Principally in mafic and ultramafic igneous and meta-igneous rocksrocks Fayalite in meta-ironstones and in some alkalic granitoidsFayalite in meta-ironstones and in some alkalic granitoidsForsterite in some siliceous dolomitic marblesForsterite in some siliceous dolomitic