Back to silicate structures:Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Pyroxene ChemistrySlide 10Orthopyroxene - ClinopyroxeneOrthopyroxene – Clinopyroxene solvus T dependenceSlide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27TectosilicatesSlide 29Slide 30Slide 31Slide 32Slide 33Igneous MineralsBack to silicate structures:Back to silicate structures:nesosilicatesnesosilicatesinosilicatesinosilicatestectosilicatestectosilicatesphyllosilicatesphyllosilicatescyclosilictaescyclosilictaessorosilicatessorosilicatesNesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2bbccprojectionprojectionInosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes TTM1M1TTCreates an “I-beam” Creates an “I-beam” like unit in the like unit in the structurestructure(+)(+)The pyroxene The pyroxene structure is then structure is then composed of composed of alternating I-beamsalternating I-beamsClinopyroxenes have Clinopyroxenes have all I-beams oriented all I-beams oriented the same: all are (+) the same: all are (+) in this orientation in this orientation (+)(+)(+)(+)(+)(+)(+)(+)(+)(+)Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes Note that M1 sites are Note that M1 sites are smaller than M2 sites, since smaller than M2 sites, since they are at the apices of the they are at the apices of the tetrahedral chainstetrahedral chainsThe pyroxene The pyroxene structure is then structure is then composed of composed of alternation I-beamsalternation I-beamsClinopyroxenes have Clinopyroxenes have all I-beams oriented all I-beams oriented the same: all are (+) the same: all are (+) in this orientation in this orientation (+)(+)(+)(+)(+)(+)Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes (+)(+)(+)(+)The pyroxene The pyroxene structure is then structure is then composed of composed of alternation I-beamsalternation I-beamsOrthoopyroxenes Orthoopyroxenes have I-beams oriented have I-beams oriented in alternate direction in alternate direction in different layersin different layers(-)(-)(+)(+)(+)(+)Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes (-)(-)(-)(-)The tetrahedral chain The tetrahedral chain above the M1s is thus above the M1s is thus offset from that below offset from that below The M2 slabs have a The M2 slabs have a similar effectsimilar effectThe result is a The result is a monoclinicmonoclinic unit cell, unit cell, hence hence clinopyroxenesclinopyroxenesInosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes ccaa(+) M1(+) M1(+) M2(+) M2(+) M2(+) M2OrthopyroxenesOrthopyroxenes have have alternating (+) and (-) alternating (+) and (-) I-beams I-beams the offsets thus the offsets thus compensate and result compensate and result in an in an orthorhombicorthorhombic unit cellunit cellInosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes ccaa(+) M1(+) M1(-) M1(-) M1(-) M2(-) M2(+) M2(+) M2Pyroxene ChemistryPyroxene ChemistryThe general pyroxene formula: The general pyroxene formula: WW1-P1-P (X,Y) (X,Y)1+P1+P Z Z22OO66WhereWhereW = W = CaCa Na NaX = X = Mg FeMg Fe2+2+ Mn Ni Li Mn Ni LiY = Al FeY = Al Fe3+3+ Cr Ti Cr TiZ = Z = SiSi Al AlAnhydrous Anhydrous so high-temperature or dry conditions so high-temperature or dry conditions favor pyroxenes over amphibolesfavor pyroxenes over amphibolesPyroxene ChemistryPyroxene ChemistryThe pyroxene quadrilateral and opx-cpx solvusThe pyroxene quadrilateral and opx-cpx solvusCoexisting opx + cpx in many rocks (pigeonite only in volcanics)Coexisting opx + cpx in many rocks (pigeonite only in volcanics) DiopsideDiopsideCaMgSiCaMgSi22OO66HedenbergiteHedenbergite CaFeSiCaFeSi22OO66Wollastonite CaWollastonite Ca22SiSi22OO66EnstatiteEnstatiteMgMg22SiSi22OO66FerrosiliteFerrosiliteFeFe22SiSi22OO66orthopyroxenesclinopyroxenespigeonite•OrthopyroxenesOrthopyroxenes – solid soln – solid soln between Enstatite-Ferrosilitebetween Enstatite-Ferrosilite•Clinopyroxenes – solid soln – solid soln between Diopside-Hedenbergitebetween Diopside-HedenbergiteJoins – lines between end Joins – lines between end members – limited mixing members – limited mixing away from joinaway from joinOrthopyroxene - ClinopyroxeneOrthopyroxene - ClinopyroxeneOPX and CPX have different crystal structures – OPX and CPX have different crystal structures – results in a complex solvus between themresults in a complex solvus between themCoexisting opx + cpx in many rocks (pigeonite only in volcanics)Coexisting opx + cpx in many rocks (pigeonite only in volcanics) DiopsideDiopsideCaMgSiCaMgSi22OO66HedenbergiteHedenbergite CaFeSiCaFeSi22OO66Wollastonite CaWollastonite Ca22SiSi22OO66EnstatiteEnstatiteMgMg22SiSi22OO66FerrosiliteFerrosiliteFeFe22SiSi22OO66orthopyroxenesclinopyroxenespigeonite(Mg,Fe)(Mg,Fe)22SiSi22OO66Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO66pigeoniteclinopyroxenesorthopyroxenesSolvusSolvus12001200ooCC10001000ooCC800800ooCCOPXOPXCPXCPXCPXCPXOPXOPXOrthopyroxene – ClinopyroxeneOrthopyroxene – Clinopyroxenesolvus T dependencesolvus T dependenceComplex solvus – the ‘stability’ of a particular mineral changes Complex solvus – the ‘stability’ of a particular mineral changes with T. A different mineral’s ‘stability’ may change with T with T. A different mineral’s ‘stability’ may change with T differently…differently…OPX-CPX exsolution lamellae OPX-CPX exsolution lamellae  Geothermometer… Geothermometer…MiscibilityGapFsFsEnEnDiDiHdHdFsFsEnEnDiDiHdHdOPXOPXOPXOPXCPXCPXCPXCPXpigeoniteaugiteorthopyroxenePigeonite + orthopyroxeneorthopyroxeneSubcalcic augitepigeoniteaugiteMiscibilityGap800800ºCºC12001200ºCºCPyroxene ChemistryPyroxene Chemistry““Non-quad” pyroxenesNon-quad” pyroxenesJadeiteJadeiteNaAlSiNaAlSi22OO66Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO66AegirineAegirineNaFeNaFe3+3+SiSi22OO66Diopside-HedenbergiteDiopside-HedenbergiteCa-Tschermack’s Ca-Tschermack’s moleculemoleculeCaAl2SiOCaAl2SiO66Ca / (Ca + Na)Ca / (Ca + Na)0.20.20.80.8Omphaciteaegirine- augiteAugiteAugiteSpodumene: Spodumene: LiAlSiLiAlSi22OO66PyroxenoidsPyroxenoids““Ideal” pyroxene chains with Ideal” pyroxene chains with 5.2 A repeat (2 tetrahedra) 5.2 A repeat (2