1. Introduction to Mineralogy Dr
Introduction to Mineralogy Dr. Tark Hamilton Chapter 18: Crystal Chemistry of Rock Forming Silicates
Camosun College GEOS 250

2. 92% of Continental & Ocean Crust is made of silicate minerals
>95% of the Upper Mantle is Olivine, Pyroxenes Plagioclase and Garnet with traces of Spinel

3. Close Packing (Electron Cloud) Model of Silica Tetrahedron

4. Silicate Anion Structural Types n. b
Silicate Anion Structural Types n.b. Cyclo includes 3, 4 & 6 member rings
Neso- Olivines, garnets, aluminosilicates
Soro-epidote group (piedmontite, allanite, zoisite), hemimorphite, vesuvianite, lawsonite
Cyclo: 3-Benitoite, 4-Papagoite, 6-Tourmaline, Cordierite & Beryl (also tecto due to AlO4 or BeO4 tetrahedra)
Ino: 1-chain Orthopyroxenes, Clinopyroxenes (Augite, Pigeonite, Spodumene, Jadeite, Omphacite), Wollastonite, Rhodonite

5. Silicate Anion Structural Types Amphiboles Micas and Frameworks
Ino: 2-Chain: Ortho: Anthophyllite-Cummintonite-Grunerite, Clino: Actinolite, Hornblende, Glaucophane, Riebeckite
Phyllo: Kaolinite, Brucite; Brucite, Gibbsite, Pyrophyllite, Talc, Phlogopite, Muscovite, Chlorite, Vermiculite, Serpentine, Palygorskite

6. 12-fold is Dodecahedral coordination, also for large cations like Ba+2 and Ra+2

7. General Silicate Formula
Xm Yn (Zp Oq) Wr
Where:
X = Large, +1 to +2, weak ≥ 8 fold cations
Y = Medium, +2 to +4, 6 fold cations
Z = Small, ≥ +3, strong 4 fold cations
W = Other anions: (OH)-, F-, Cl-,(SO4)-2,(CO 3) -2
p/q depends on polyhedral polymerization
m, n & r depend on valence & neutrality

8. Nesosilicates: Olivine Group
Ordinary Olivine series: Orthorhombic
Forsterite: Mg2SiO4
Fayalite: Fe2SiO4
Liebenbergite: (Ni,Mg)2SiO4
Tephroite: Mn2SiO4
Monticellite: CaMgSiO4
Kirschsteinite: CaFeSiO4
Glaucochroite: CaMnSiO4
Olivine and Spinel are important mineral repositories for Ni in the Mantle, Meteorites and Ultramafic Igneous Rocks

9. Forsterite Fayalite Monticellite Glaucochroite
Forsterite-R. Lavinsky, St.John’s Island Red Sea Egypt Peridote > 1.4 cm; Fayalite-L.Mattei Montenero quarry Onano Italy,
K.Nash photo-Monticellite Magnet Cove Arkansas Carbonatite, Glaucochroite-P.Cristofono, Franklin Mine N.J. w/green Willemite & black Franklinite

10. Olivine Structure projected on (100) Octahedra: M2 is ~regular M1 distorted
(Mg,Fe,Ni)2SiO4
M1 vs M2 Thermometer
Because of edge sharing between M1-M1 and M1-M2, M1 is distorted, while M2 is larger and somewhat more regular. The distortion decreases with increasing temperature as molar volume increases.
Ergo, Mg-Fe partitioning between co-existing Olivines and spinels or other silicates constitute good geothermometers as does Ni content in these same phases.
Notice all silica tetrahedra are isolated and de-polymerized from one-another.
M1 distortion
= F (Temperature)

11. Nesosilicates: Garnet Group
Pyralspite series:
Pyrope: Mg3 Al2 Si3 O12
Almandine: Fe3 Al2 Si3 O12
Spessartine: Mn3 Al2 Si3 O12
Ugrandite series:
Uvarovite: Ca3 Cr2 Si3 O12
Grossularite: Ca3 Al2 Si3 O12
Andradite: Ca3 Fe+32 Si3 O12
Alternative classifications stress Uvarovite as the Cr-garnet, Andradite as the Ferri-garnet and all others are Al-Garnets.
This suits their distribution in Ultramafic rocks, Oxidized Skarns and Aluminous Metasediments respectively.

12. Almandine-Australia Spessartine-Australia
D.Sheumack Almandines to 10 cm, Yankowinna Australia, Weinrich-Spessartine (Broken Hill), Kristalle-Finland Uvarovite photo, Lavinsky-Afghanistan Andradite photo
Uvarovite-Finland Andradite-Afghanistan

13. Garnet Structure on [001] Lone Tetrahedra, Octahedra & Distorted Cubes
A-larger 8 fold distorted cubes (actually triangular dodecahedra): Mg, Fe2+, Mn2+, Ca; B-smaller octahedra: Al, Cr+3, Fe+3.
Note Cubes share edges with other cubes, octahedra and tetrahedra, so these sites are the most distorted.

14. Aluminosilicate Group
Al2 SiO5 (mostly orthorhombic) PT indicators
Andalusite: moderate P/T meta-rocks
½ Al in octahedral chains, ½ as Al-5fold/Si-4 chains
Kyanite (Triclinic): Hi P/T meta-rocks
All Al is octahedral in chains || to C or lone octahedra
Sillimanite: Hi T/P meta-rocks
Octahedral Al chains & || tetrahedral chains Al/Si/Al/Si..
Mullite: Very High T contact meta
Al8 ((Si,Al)O4) 4 (O,OH,F)
At Andalusia Spain most Andalusite is retrograded to Muscovite. Kyanite is named of its usual blue (cyan) colour.

15. Kyanite on [001] edge sharing octahedra II to c
All Al in Octahedra, chains parallel to C or lone octahedra

16. Andalusite var. Chiastolite Kyanite (below) Sillimanite var. Fibrolite
Andalusite-R. Currier S.Australia, Kyanite-M. Olsina, San Luis Argentina, Sillimanite-S.Varna , Bohemia Czech Republic

17. Sillimanite (left) & Andalusite (right) [Al]VI & [Al-Si]IV chains II to c

18. Mullite: Isle of Mull Eifel (S.Wolfsreid), Rotorua (M.leGras)
Contact metamorphism of shales and miarolitic cavities in alkaline and mafic lavas

19. Sorosilicate “anion-dimer”

20. Sorosilicate Group Epidote Ca Al Clinozoisite Ca Fe+3 , Al
Ions in Ca site Ions in Al site (non-chain)
Epidote Ca Al
Clinozoisite Ca Fe+3 , Al
Piedmontite Ca Mn+3, Fe+3, Al
Allanite: Na, Ca, Ce, La Mg Fe+2 Fe+3 Al
Zoisite Ca Fe+3 , Al

21. Epidote unit cell on [010]

22. Epidote versus Zoisite (Monoclinic vs Orthorhombic)

23. Allanite-Black Zoisite var Thulite-pink Epidote-Green Tanzanite-3chroic
Epidote-P.Gundersen, Allanite-Creative Commons Mt. Isa Queensland Australia, Zoisite-M.Wilson P.Q. Abitibi-Temiskaming,
Tanzanite-R.Lavinsky
Allanite is a source of Ce, La and Nd Rare Earth Elements for magnets and high tech applications

24. Cyclosilicates
Benitoite
Beryl & Tourmaline
Papagoite

25. 6 member Cyclosilicate Group
Beryl:
Borosilicate with up to 7 different ions or vacancies!
Tourmaline:
Cordierite

26. Beryl (a) on (0001) w/ unit cell & (b) parallel to C axis vertical
Emerald & Aquamarine

27. Beryl: Aquamarine, Emerald, Morganite
Aquamarine-J.Betts Pakistan, Emerald & Morganite both Pakistan by R. Lavinsky

28. Low Cordierite’s Al-Si backbone Orthorhombic, pseudo-hexagonal
High Cordierite: Indialite
Is Hexagonal

29. Cordierite Red Trilings & Blue on Quartz
Cordierite-Ruttan Lake Mine Manitoba, Cordierite trilings (pseudohexagonal)Eich Germany, S.Krotkin

30. Tourmaline End Members & Substitutions-Site Occupancies

31. Tourmaline a (0001) & b C vertical

32. Tourmaline: Elbaite Dravite
Dravite-A. Schreilechner Afghanistan; Elbaite-Watermelon Tourmaline R.Lavinsky, Kabul Afghanistan

33. Pyroxene Wollastonite Rhodonite Pyroxmangite

34. Pyroxene Ca-Mg-Fe Classification Triangles

35. Chain Silicates: Cation Sites & Substitutions

36. (SiO3)-2 Single Chain Polymer

37. Jadeite NaAl(SiO3)2 Structure on [100]

38. Jadeite
Jadeite-W.Henkel, Myanmar, chipped pebble

39. Monoclinic Pyroxene projected onto [001]

40. Unit Cells of Enstatite & Diopside projected on [010]
Orthorhombic
Monoclinic
Who has the larger unit cell & mirror plane?
Could pyroxenes exhibit exsolution? Why or not?

41. Amphibole Compositions in the Ca-Mg-Fe Triangle
Hypothetical
End member
Monoclinic
Orthorhombic

42. Orthorhombic Ferro-Actinolite Anthophyllite Grunerite Var. Amosite
                                                                                                                                                                                                                                                                                                                                                            
Orthorhombic
Ferro-Actinolite
Anthophyllite
Grunerite
Var. Amosite

43. C2/m Amphibole on [100] 2 anion sites, 7 cation sites!

44. Chain Silicates: Cation Sites & Substitutions

45. C2/m Amphibole on [001] T-O-T strips: prismatic habit and cleavage

46. Intergrowth of 2 polymorphs of: Na0.1Fe2.2Mg4.5Al0.1Si8O22(OH)2
Monoclinic
Tremolite
Orthorhombic
Who has the larger unit cell & mirror plane?
What site is Na+ in?
What site is Al+3 in?
Could amphiboles exhibit exsolution? Why or not?

47. “Biopyriboles” Mixing single, double and triple chain repeats
Single - Enstatite: MgSiO3
Double - Anthophyllite: Mg7Si8O22(OH)2
Quadruple-singles – Aenigmatite: Na2Fe5TiSi6O20
Triple - Jimtompsonite: (Mg,Fe)10Si12O32(OH)4
Double/Triple Pairs- Chesterite: (Mg,Fe)17Si20O54(OH)6

48. “Biopyriboles” Mixing single, double and triple chain repeats
Aenigmatite
Repeats groups of 4 single chains

49. Aenigmatite: Na2Fe5TiSi6O18O2 Triclinic Striated blades: Grey, Black, Bronze G. Fretti San Miguel Azores
In strongly alkaline and peralkaline igneous rocks with sodic amphiboles and pyroxenes

50. Phyllosilicates (Micas & Clays)
Undistorted Hexagonal Ring in an Si2O5 sheet
(Triangles in tetrahedra = triangles in octahedra)

51. “Infinite” Octahedral sheet All Octahedra rest on triangular faces
XO6 octahedra, other transition metals substitute

52. Triclinic (pseudo-hexagonal) Named for Gao-Ling, China
Kaolinite T/O Structure & Pigg’s Egg (pseudomorph after orthoclase, Cornwall)
Al2 Si2O5 (OH)4
Triclinic (pseudo-hexagonal)
(due to T/O stack)
Named for Gao-Ling, China

53. Muscovite KAl2 [AlSi3O10] (OH)2 (Plan View) Octahedral Sheet smaller, Tetrahedra rotate
Opposed rotations of adjacent tetrahedra makes this sheet Trigonal
Slight offset of C axis from vertical makes it 2/m Monoclinic overall
Slanted books from Minas Gerias Brazil show crystal habit.
Fuchsite (Bahia Brazil has Cr+3 for Al+3 in ________ site.
Named for Muscovy Glass from Urals
Muscovite books and Fuchsite (Cr-Bearing). Perfect basal cleavage through large weak infrequent K+ 12-fold sites

54. Muscovite (T-O-T-I… Structure) Where is the cleavage? What bond type?
K [ ]Al2 [AlSi3O10] (OH)2
Muscovite is a
Dioctahedral mica
(2 of every 3 sites have Al)
[Vacant] i

55. Misfit of T-O Sheets on [010] Makes mica structures Monoclinic

56. 2M & 3T Polytypes in Micas arise from (OH)/Hex stacking rotations

57. 10, 20 & 30 Angstrom Stacking of Mica Polytypes – Clays & Soils

58. Pyrophyllite T-O-T Layer “Fire-leaf”
Al2 Si4O10 (OH)2
Monoclinic (due to stack)
Hydrothermal veins & schists, Belgium

59. Trioctahedral Micas have 3/3 of the Octahedral sites filled
Trioctahedral Micas have 3/3 of the Octahedral sites filled. Dioctahedral Micas have 2/3 of the Octahedral sites filled. Which are Biotite & Chlorite? Mg Al

60. Chlorite Group: (T-O-T)-I-(T-O-T) 12 Triclinic or Monoclinic Structures
The general formula may be stated:
A5-6T4Z18 .
A = Al, Fe+2, Fe+3, Li, Mg, Mn, or Ni
T = Al, Fe+3, Si, and Z = O and/or OH.
However this is clearer as:
(Mg, Fe+2, +3, Al)3 (Al, Si)4 O10 (OH)2 –
(Mg, Fe+2, +3, Al)3 (OH)2
because there are 2
distinct structural units Talc & Brucite

61. Vermiculite: (T-O-T)-2H2O-(T-O-T)
Exchangeable
Cations
(Mg,)3 (Al, Si)4 O10 (OH)2
– 4.5 H2O (Mg)0.35 -
Monoclinic

62. Serpentine: Crysotile vs. Antigorite
(Mg,Fe+2)3 Si2O5 (OH)4
Monoclinic
Partial bending
Accomodates misfit
of T-O Layers

63. 2 different Polytypes for Serpentine from stacking offsets of T-O sheets

66. Structures of SiO2 Polymorphs Beta Quartz, Chalcedony, Agate
Alpha – High Quartz on (0001)
4 unit cells with 62 screw axes
Fractional heights noted on tetrahedra
b) Beta – Low Quartz
4 unit cells with 32 screw axes

67. Structures of SiO2 Polymorphs
a Tridymite (0001)
Eifel
b Cristobalite (111)
Italy
c Coesite (001)
Behringer, AZ
d Stishovite (100)
Bisbee, AZ

68. P-T Phase Diagram for SiO2 Polymorphs (Where would these form?)

69. Feldspars: Compositions & Classification of Hi T Phases
Sanidine Monoclinic 5 cm, has Carlsbad twin with axis lying in twin plane, Samothraki Is, Greece.
Blue triclinic anorthoclase 60 cm from Mt Erebus volcano, Rossland, Antarctica. Albite Clevelandite and Labradorite as typical.
Albite (Moonstone) var. Peristerite, Delaware Co, Pennsylvania.
Labradorite from Labrador with Killer Schiller!

70. Hi Sanidine on (201)

71. 4-Membered Tetrahedral Chains Parallel to a axis in Feldspars Si4O8 Framework  (Na,K)(AlSi3 O8) or Ca(Al2 Si2O8)
Similar to a stuffed Silica structure,
Incorporating Al into tetrahedra
With larger cations in voids.
In Hi Sanidine, Al & Si are disordered
(random) intetrahedral sites.
Monoclinic 2/m symmetry
K+ in distorted 9 fold voids.
Microcline, Low-T, is Triclinic
Al &Si ordered but K+ in random voids

72. Miscibility Gap for Alkali Feldspars at T < 650°C, Leucite can’t exist in plutons
And Muscovite can’t exist except as accidental xenocrysts in volcanics!

73. Possible Cooling Paths and Phase changes for Hi Sanidine

74. Experimental Solid Solution in Or-Ab-An

75. Plagioclase Feldspar Phase Diagram Almost complete solid solution, miscibility

76. Or-Ab-An versus Temperature Thermal topology of the feldspar system
Cotectic trough
Bowen’s Continuous
Reaction Series
Solvus
Solvi

77. Feldspathoids: Silica Undersaturated Tectosilicates
Nepheline and eudialyte (pink) Ne-syenite, Mot St. Hilare P.Q.
Leucite, Tetragonal, Eifel Mtns. Germany.
Kalsilite tabular hexagonal crystals, (mineral name from pronouncing its chemical formula!), with pyroxene and apatite, Eifel Mtns.

78. Leucite Structure down [001], c axis
Leucite phenocryst in undersaturated trachyte, Kaiserstuhl, Germany.

79. Nepheline Kalsilite Structure on (0001) There are 4 distinct tetrahedral sites.
Hexagonal and Square Nepheline from Dungannon Ontario,

80. Sodalite Na2(AlSiO4)6Cl2 Hackmanite,Nosean, Hauyne
Hackmanite purple isometric on marble Afghanistan. Fluorescent and phosphorescent! Also blue & white varieties.
Also found at Halliburton-Bancroft Ontario in metasomatic rocks.

81. Chains of Tetrahedra in Fibrous Zeolites Natrolite Na2Al2Si3O10 2H2O
Radial, concentric and slender blades.

82. Chabazite: Ca2Al2Si4O12 6H2O open channels for water, ion exchange
Na, Sr, K varieties exist, triclinic generally. Specimens from New South Wales and Queensland, Aus.

83. Thermal Gravimetric Curves fro water loss on heating
Thermal Gravimetric Curves fro water loss on heating. This is reversible unlike loss of hydrogen or OH groups from other silicates.

84. Zeolite Molecular Sieve can separate n-alkanes from branched iso-alkanes Ion exchange properties allows a strong solution of one cation to displace another.

85. There is always room for a new mineral or another unique occurrence!