MOST IMPORTANT MINERAL
SUITE:
The Silicate Minerals
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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
Silica Chains and Octahedra
Silica Chains and Octahedra
Two Sites in Pyroxenes
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
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 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 KFeldspar
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