SiO2TectosilicatesSlide 3Slide 4Slide 5Slide 6MicasSlide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Aluminosilicate MineralsSlide 16Serpentine MineralsSlide 18Slide 19Slide 20Chlorite GroupTalcPrehnite-PumpellyiteZeolitesEpidote GroupSlide 26StauroliteMetamorphic chain silicatesMetamorphic faciesSlide 30The Phase Rule in Metamorphic SystemsLet’s put it all together…Slide 33Slide 34SiO2StishoviteCoesite- quartz- quartzLiquidTridymiteCristobalite600 1000 1400 1800 2200 2600246810Pressure (GPa)Temperature oCAfter Swamy and Saxena (1994) J. Geophys. Res., 99, 11,787-11,794.TectosilicatesLow Quartz001 Projection Crystal Class 32001 Projection Crystal Class 32StishoviteCoesite- quartz- quartzLiquidTridymiteCristobaliteTectosilicatesHigh Quartz at 581oC001 Projection Crystal Class 622001 Projection Crystal Class 622StishoviteCoesite- quartz- quartzLiquidTridymiteCristobaliteTectosilicatesCristobalite001 Projection Cubic Structure001 Projection Cubic StructureStishoviteCoesite- quartz- quartzLiquidTridymiteCristobaliteTectosilicatesStishoviteHigh pressure High pressure  Si SiVIVIStishoviteCoesite- quartz- quartzLiquidTridymiteCristobaliteTectosilicatesLow Quartz StishoviteSiSiIVIV Si SiVIVIMicas•Biotite and Muscovite are also important metamorphic minerals (muscovite often the principle component of schists)•Phlogopite – similar to biotite, but has little iron, forms from Mg-rich carbonate deposits and a common mineral in kimberlites (diamond-bearing material)•Sericite – white mica (similar to muscovite) – common product of plagioclase feldspar alteration at low gradesSiOSiO44 tetrahedra polymerized into 2-D sheets: [Si tetrahedra polymerized into 2-D sheets: [Si22OO55]]Apical O’s are unpolymerized and are bonded to other Apical O’s are unpolymerized and are bonded to other constituentsconstituentsPhyllosilicatesPhyllosilicatesTetrahedral layers are bonded to octahedral layers Tetrahedral layers are bonded to octahedral layers (OH) pairs are located in center of T rings where no apical (OH) pairs are located in center of T rings where no apical OOPhyllosilicatesPhyllosilicatesOctahedral layers can be understood by analogy with hydroxidesOctahedral layers can be understood by analogy with hydroxidesPhyllosilicatesPhyllosilicatesBrucite: Mg(OH)Brucite: Mg(OH)22Layers of octahedral Mg Layers of octahedral Mg in coordination with in coordination with (OH)(OH)Large spacing along Large spacing along cc due to weak van der due to weak van der waals bondswaals bondsccPhyllosilicatesPhyllosilicatesGibbsite: Al(OH)Gibbsite: Al(OH)33Layers of octahedral Al in coordination with (OH)Layers of octahedral Al in coordination with (OH)AlAl3+3+ means that means that only 2/3 of the VI sites may be occupiedonly 2/3 of the VI sites may be occupied for charge-balance for charge-balance reasonsreasonsBrucite-type layers may be called Brucite-type layers may be called trioctahedraltrioctahedral and gibbsite-type and gibbsite-type dioctahedraldioctahedralaa11aa22PhyllosilicatesPhyllosilicatesMuscovite:Muscovite: KK Al Al22 [Si [Si33AlAlOO1010] (OH)] (OH)2 2 (coupled K - Al(coupled K - AlIVIV))T-layer - T-layer - didiocathedral (Alocathedral (Al3+3+) layer - T-layer - ) layer - T-layer - KKT T O O T T KK T T O O T T KK T T O O TTK between T - O - T groups is stronger than vdwK between T - O - T groups is stronger than vdwPhyllosilicatesPhyllosilicatesPhlogopite:Phlogopite: K Mg K Mg33 [Si [Si33AlOAlO1010] (OH)] (OH)22T-layer - T-layer - tritriocathedral (Mgocathedral (Mg2+2+) layer - T-layer - ) layer - T-layer - KKT T O O T T KK T T O O T T KK T T O O TTK between T - O - T groups is stronger than vdwK between T - O - T groups is stronger than vdwAluminosilicate MineralsAndalusite Kyanite Sillimanite•SILLIMANITE: Orthorhombic: Octahedral Al chains (6-fold) are crosslinked by both Si and Al tetrahedra (4-fold).•ANDALUSITE: Orthorhombic: 5-coordinated Al; Same octahedral (6-fold) chains.•KYANITE: Triclinic: All the Al is octahedrally coordinated (6- and 6-fold). •Clearly, changes in structure are in response to changing P and T. Result is changes in Al coordination. •Phase transformations require rebonding of Al. Reconstructive polymorphism requires more energy than do displacive transformations. Metastability of these 3 are therefore important (Kinetic factors limit equilibrium attainment).•All 3 are VERY important metamorphic index minerals.Aluminosilicate Minerals•3 polymorphs of Al2SiO5 are important metamorphic mineralsAndalusite Kyanite SillimaniteSerpentine Minerals•Mg3Si2O5(OH)4 minerals (principally as antigorite, lizardite, chrysotile polymorphs)•Forms from hydration reaction of magnesium silicates–Mg2SiO4 + 3 H2O  Mg3Si2O5(OH)4 + Mg(OH)2forsterite serpentine brucite•Asbestosform variety is chrysotile (accounts for 95% of world’s asbestos production  MUCH LESS DANGEROUS than crocidolite)PhyllosilicatesSerpentine:Serpentine: Mg Mg33 [Si [Si22OO55] (OH)] (OH)44T-layers and T-layers and tritriocathedral (Mgocathedral (Mg2+2+) layers ) layers (OH) at center of T-rings and fill base of VI layer (OH) at center of T-rings and fill base of VI layer Yellow = (OH)Yellow = (OH)T T O O -- T T O O -- T T OOvdwvdwvdwvdwweak van der Waals bonds between T-O groups weak van der Waals bonds between T-O groupsSerpentineOctahedra are a bit larger than tetrahedral Octahedra are a bit larger than tetrahedral match, so they cause bending of the T-O match, so they cause bending of the T-O layers (after Klein and Hurlbut, 1999).layers (after Klein and Hurlbut, 1999).Antigorite maintains a Antigorite maintains a sheet-like form by sheet-like form by alternating segments of alternating segments of opposite curvatureopposite curvatureChrysotile does not do this Chrysotile does not do this and tends to roll into tubesand tends to roll into tubesSerpentineThe rolled tubes in chrysotile resolves the apparent The rolled tubes in chrysotile resolves the apparent paradox of asbestosform sheet silicatesparadox of asbestosform sheet silicatesS = serpentine T = talcS = serpentine T = talcNagby and Faust (1956) Am. Mineralogist 41, 817-836.Veblen and Busek, 1979, Science 206, 1398-1400.Chlorite Group•Another phyllosilicate, a group of difficult to distinguish minerals•Typically green, and the dominant and characteristic mineral of greenschist facies