MOST IMPORTANT MINERAL SUITE the silicate minerals

MOST IMPORTANT MINERAL SUITE: The Silicate Minerals • Si + O = 75% of Crust • Silicates make up 95% + of all Rocks • SiO4: -4 charge • Link Corner-To-Corner by Sharing Oxygen atoms Representatives: •Garnet •Kyanite •Olivine •Zircon •Topaz •Staurolite •Sphene SiO4 in Formula Nesosilicates Isolated Tetrahedra Sorosilicates - Paired Tetrahedra •Epidote is the most common example •Lawsonite •Vesuvianite Si2O7 in Formula Cyclosilicates - Rings •Beryl (Emerald) •Cordierite •Tourmaline SinO3n in Formula What is a Tetrahedron? • In many silicates, Al, Be and other ions occur in tetrahedral coordination • Substitution of Al for Si maintains charge balance in Feldspars • Some mineralogists count all tetrahedra in classifying structure • By this criterion, Beryl and Cordierite are tectosilicates Inosilicates - Chains Single Chains (Pyroxenes) SiO3 or Si2O6 in Formula More Realistic Picture Major Pyroxenes • Ferromagnesian – Enstatite (MgSiO3) – Hypersthene (Mg,Fe)SiO3 • Calcic – Diopside: CaMgSi2O6 – Pigeonite: Ca0.25(Mg,Fe)1.75Si2O6 – Hedenbergite: CaFeSi2O6 • Augite: XYZ2O6 Other Pyroxenes • Sodic – Jadeite: NaAlSi2O6 • Breakdown of Na-Feldspar • High Pressure Metamorphism – Aegerine (Acmite) NaFe3Si2O6 • Spodumene: LiAlSi2O6 – Pegmatite Mineral Pyroxenes and Cations Rhodonite Pyroxmangite Biopyriboles • Biotite = Silica sheets with (Mg,Fe) Sheets in between • Amphiboles and Pyroxenes are strips of Biotite sheets • Biopyribole = Biotite + Pyroxene + Amphibole Inosilicates - Chains Double Chains (Amphiboles Si4O11 in Formula) Major Amphiboles • Anthophyllite (Mg,Fe)7Si8O22(OH)2) • Cummingtonite (Fe2Mg5Si8O22(OH)2) -Grunerite (Fe7Si8O22(OH)2) • Tremolite (Ca2Mg5Si8O22(OH)2) – Actinolite (Ca2(Mg,Fe)5Si8O22(OH)2) • Hornblende (X2-3Y5Z8O22(OH)2) • Glaucophane (Na2Mg3Al2Si8O22(OH)2) and Riebeckite (Na2Fe++3,Fe+++2Si8O22(OH)2) Beyond Amphiboles • There are a few 3-chain and mixed chain silicates • Discovered only in 1970’s • Occur in asbestos Phyllosilicates – Sheets (Si2O5 in Formula) Phyllosilicates - Sheets Si2O5 sheets with layers of Mg(OH)2 or Al(OH)3 • Micas • Clay minerals • Talc • Serpentine (asbestos) minerals Tectosilicates - ThreeDimensional Networks • Quartz Feldspars Tectosilicates • Quartz and Polymorphs • Feldspars – K-Feldspars (KAlSi3O8) – Plagioclase (NaAlSi3O8)- (CaAl2Si2O8) – Barium Feldspars (BaAl2Si2O8) • Feldspathoids (Foids) • Scapolites • Zeolites K-Feldspars and Mixtures • – – – • K-Feldspars (KAlSi3O8) Microcline (Slow cooling) Orthoclase (Faster cooling) Sanidine (Fastest cooling, High T) Anorthoclase: Solid solution of K-Feldspar and Albite (NaAlSi3O8) • Perthite: K-Feldspar with exsolved plagioclase • Antiperthite: Plagioclase with exsolved K-Feldspar Plagioclase • Solid solution of Albite (NaAlSi3O8) and Anorthite (CaAl2Si2O8) • 0-10% An = Albite: Na-Metasomatism • 10-30% An = Oligoclase: Granites • 30-50% An = Andesine: Andesites and Diorite • 50-70% An = Labradorite: Basalt and Gabbro • 70-90% An = Bytownite: Rarest • 90-100% An = Anorthite: Metamorphic Feldspathoids (Foids) • Fill “ecological niche” of feldspars in Si-poor rocks • Never occur with quartz • Leucite (KAlSi2O6) • Nepheline ((Na,K)AlSiO4) Scapolites and Relatives • Sodalite (Na8(AlSiO4)6Cl2) • Lazurite (Na,Ca)8(AlSiO4)6(SO4,S,Cl)2) • Scapolite – Marialite = Albite + NaCl – Meionite = Anorthite + CaSO4 or CaCO3 [...]... (Na2Fe++3,Fe+++2Si8O22(OH)2) Beyond Amphiboles • There are a few 3-chain and mixed chain silicates • Discovered only in 1970’s • Occur in asbestos Phyllosilicates – Sheets (Si2O5 in Formula) Phyllosilicates - Sheets Si2O5 sheets with layers of Mg(OH)2 or Al(OH)3 • Micas • Clay minerals • Talc • Serpentine (asbestos) minerals Tectosilicates - ThreeDimensional Networks • Quartz Feldspars Tectosilicates • Quartz and Polymorphs... charge for Fe and Mg – Pure Mn true pyroxenes exist – These have complex chains because of variable compositions Wollastonite CaSiO3 Wollastonite End-On Rhodonite Pyroxmangite Biopyriboles • Biotite = Silica sheets with (Mg,Fe) Sheets in between • Amphiboles and Pyroxenes are strips of Biotite sheets • Biopyribole = Biotite + Pyroxene + Amphibole Inosilicates - Chains Double Chains (Amphiboles Si4O11 ... of Mg(OH)2 or Al(OH)3 • Micas • Clay minerals • Talc • Serpentine (asbestos) minerals Tectosilicates - ThreeDimensional Networks • Quartz Feldspars Tectosilicates • Quartz and Polymorphs • Feldspars... •Sphene SiO4 in Formula Nesosilicates Isolated Tetrahedra Sorosilicates - Paired Tetrahedra •Epidote is the most common example •Lawsonite •Vesuvianite Si2O7 in Formula Cyclosilicates - Rings •Beryl... (Na2Fe++3,Fe+++2Si8O22(OH)2) Beyond Amphiboles • There are a few 3-chain and mixed chain silicates • Discovered only in 1970’s • Occur in asbestos Phyllosilicates – Sheets (Si2O5 in Formula) Phyllosilicates - Sheets Si2O5