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Presentation on theme: "MOST IMPORTANT MINERAL SUITE: The Silicate Minerals"— Presentation transcript:

Si + O = 75% of Crust Silicates make up 95% + of all Rocks SiO4: -4 charge Link Corner-To-Corner by Sharing Oxygen atoms

2 Nesosilicates - Isolated Tetrahedra
Representatives: Garnet Kyanite Olivine Zircon Topaz Staurolite Sphene SiO4 in Formula

3 Sorosilicates - Paired Tetrahedra
Epidote is the most common example Lawsonite Vesuvianite Si2O7 in Formula

4 Cyclosilicates - Rings
Beryl (Emerald) Cordierite Tourmaline SinO3n in Formula

5 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

6 Single Chains (Pyroxenes) SiO3 or Si2O6 in Formula
Inosilicates - Chains Single Chains (Pyroxenes) SiO3 or Si2O6 in Formula

7 More Realistic Picture

8 Major Pyroxenes Ferromagnesian Calcic Augite: XYZ2O6
Enstatite (MgSiO3) – Hypersthene (Mg,Fe)SiO3 Calcic Diopside: CaMgSi2O6 Pigeonite: Ca0.25(Mg,Fe)1.75Si2O6 Hedenbergite: CaFeSi2O6 Augite: XYZ2O6

9 Other Pyroxenes Sodic Spodumene: LiAlSi2O6 Jadeite: NaAlSi2O6
Breakdown of Na-Feldspar High Pressure Metamorphism Aegerine (Acmite) NaFe3Si2O6 Spodumene: LiAlSi2O6 Pegmatite Mineral

10 Pyroxenes and Cations

11 Silica Chains and Octahedra

12 Silica Chains and Octahedra

13 Two Sites in Pyroxenes

14 Pyroxenoids Have single chains but more complex bends to accommodate cations Lack pyroxene cleavage Wollastonite (CaSiO3) Rhodonite and Pyroxmangite (MnSiO3) Mn is a good match in size and charge for Fe and Mg Pure Mn true pyroxenes exist These have complex chains because of variable compositions

15 Wollastonite CaSiO3

16 Wollastonite End-On

17 Rhodonite

18 Pyroxmangite

19 Biopyriboles Biotite = Silica sheets with (Mg,Fe) Sheets in between
Amphiboles and Pyroxenes are strips of Biotite sheets Biopyribole = Biotite + Pyroxene + Amphibole

20 Double Chains (Amphiboles Si4O11 in Formula)
Inosilicates - Chains Double Chains (Amphiboles Si4O11 in Formula)

21 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)

22 Beyond Amphiboles There are a few 3-chain and mixed chain silicates
Discovered only in 1970’s Occur in asbestos

23 Phyllosilicates – Sheets (Si2O5 in Formula)


25 Phyllosilicates - Sheets
Si2O5 sheets with layers of Mg(OH)2 or Al(OH)3 Micas Clay minerals Talc Serpentine (asbestos) minerals

26 Tectosilicates - Three-Dimensional Networks
Quartz Feldspars

27 Tectosilicates Quartz and Polymorphs Feldspars Feldspathoids (Foids)
K-Feldspars (KAlSi3O8) Plagioclase (NaAlSi3O8)- (CaAl2Si2O8) Barium Feldspars (BaAl2Si2O8) Feldspathoids (Foids) Scapolites Zeolites

28 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

29 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

30 Feldspathoids (Foids)
Fill “ecological niche” of feldspars in Si-poor rocks Never occur with quartz Leucite (KAlSi2O6) Nepheline ((Na,K)AlSiO4)

31 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

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