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

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

Close Packing (Electron Cloud) Model of Silica Tetrahedron

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

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

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

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

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

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

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)

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.

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

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.

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.

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

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

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

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

Sorosilicate “anion-dimer”

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

Epidote unit cell on [010]

Epidote versus Zoisite (Monoclinic vs Orthorhombic)

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

Cyclosilicates Benitoite Beryl & Tourmaline Papagoite

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

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

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

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

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

Tourmaline End Members & Substitutions-Site Occupancies

Tourmaline a (0001) & b C vertical

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

Pyroxene Wollastonite Rhodonite Pyroxmangite

Pyroxene Ca-Mg-Fe Classification Triangles

Chain Silicates: Cation Sites & Substitutions

(SiO3)-2 Single Chain Polymer

Jadeite NaAl(SiO3)2 Structure on [100]

Jadeite Jadeite-W.Henkel, Myanmar, chipped pebble

Monoclinic Pyroxene projected onto [001]

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?

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

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

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

Chain Silicates: Cation Sites & Substitutions

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

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?

“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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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!

Hi Sanidine on (201)

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

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!

Possible Cooling Paths and Phase changes for Hi Sanidine

Experimental Solid Solution in Or-Ab-An

Plagioclase Feldspar Phase Diagram Almost complete solid solution, miscibility

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

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.

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

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

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.

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

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

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.

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

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