most important mineral suite: the silicate minerals
DESCRIPTION
MOST IMPORTANT MINERAL SUITE: The Silicate Minerals. Si + O = 75% of Crust Silicates make up 95% + of all Rocks SiO 4 : -4 charge Link Corner-To-Corner by Sharing Oxygen atoms. Nesosilicates - Isolated Tetrahedra. Representatives: Garnet Kyanite Olivine Zircon Topaz Staurolite - PowerPoint PPT PresentationTRANSCRIPT
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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
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Nesosilicates - Isolated Tetrahedra
Representatives:•Garnet •Kyanite •Olivine•Zircon•Topaz•Staurolite•Sphene
SiO4 in Formula
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Sorosilicates - Paired Tetrahedra
•Epidote is the most common example
•Lawsonite
•Vesuvianite
Si2O7 in Formula
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Cyclosilicates - Rings
•Beryl (Emerald) •Cordierite•Tourmaline
SinO3n in Formula
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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
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Inosilicates - Chains Single Chains (Pyroxenes) SiO3 or Si2O6 in Formula
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More Realistic Picture
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Major Pyroxenes• Ferromagnesian
– Enstatite (MgSiO3) – Hypersthene (Mg,Fe)SiO3
• Calcic– Diopside: CaMgSi2O6
– Pigeonite: Ca0.25(Mg,Fe)1.75Si2O6
– Hedenbergite: CaFeSi2O6
• Augite: XYZ2O6
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Other Pyroxenes• Sodic
– Jadeite: NaAlSi2O6 • Breakdown of Na-Feldspar• High Pressure Metamorphism
– Aegerine (Acmite) NaFe3Si2O6
• Spodumene: LiAlSi2O6 – Pegmatite Mineral
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Pyroxenes and Cations
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Silica Chains and Octahedra
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Silica Chains and Octahedra
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Two Sites in Pyroxenes
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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
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Wollastonite CaSiO3
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Wollastonite End-On
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Rhodonite
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Pyroxmangite
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Biopyriboles• Biotite = Silica sheets with (Mg,Fe) Sheets
in between• Amphiboles and Pyroxenes are strips of
Biotite sheets• Biopyribole = Biotite + Pyroxene +
Amphibole
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Inosilicates - Chains Double Chains (Amphiboles Si4O11 in Formula)
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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)
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Beyond Amphiboles
• There are a few 3-chain and mixed chain silicates
• Discovered only in 1970’s• Occur in asbestos
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Phyllosilicates – Sheets (Si2O5 in Formula)
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Phyllosilicates - Sheets
Si2O5 sheets with layers of Mg(OH)2 or Al(OH)3
• Micas• Clay minerals• Talc• Serpentine (asbestos) minerals
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Tectosilicates - Three-Dimensional Networks
• Quartz Feldspars
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Tectosilicates• Quartz and Polymorphs• Feldspars
– K-Feldspars (KAlSi3O8)
– Plagioclase (NaAlSi3O8)- (CaAl2Si2O8)
– Barium Feldspars (BaAl2Si2O8)
• Feldspathoids (Foids)• Scapolites• Zeolites
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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
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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
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Feldspathoids (Foids)• Fill “ecological niche” of feldspars in Si-poor
rocks• Never occur with quartz• Leucite (KAlSi2O6)
• Nepheline ((Na,K)AlSiO4)
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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