1. 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

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