Introduction to MineralogyIntroduction to MineralogyDr. Tark HamiltonDr. Tark Hamilton

Chapter 18: Chapter 18: Crystal Chemistry of Rock Crystal Chemistry of Rock

Forming SilicatesForming Silicates

Camosun College GEOS 250Camosun College GEOS 250

92% of Continental & Ocean Crust is 92% of Continental & Ocean Crust is made of silicate mineralsmade of silicate minerals

>95% of the >95% of the Upper Mantle Upper Mantle is Olivine, is Olivine, Pyroxenes Pyroxenes Plagioclase Plagioclase and Garnet and Garnet with traces of with traces of SpinelSpinel

Close Packing (Electron Cloud) Close Packing (Electron Cloud) Model of Silica TetrahedronModel of Silica Tetrahedron

Silicate Anion Silicate Anion Structural TypesStructural Types

n.b. Cyclo n.b. Cyclo includes 3, 4 & 6 includes 3, 4 & 6

member ringsmember rings

Silicate Anion Silicate Anion Structural TypesStructural Types

Amphiboles Amphiboles Micas and Micas and

FrameworksFrameworks

General Silicate FormulaGeneral Silicate Formula XXmm YYnn ( (ZZpp O Oqq) ) WWrr

Where:Where: XX = Large, +1 to +2, weak = Large, +1 to +2, weak ≥ ≥ 8 fold cations8 fold cations YY = Medium, +2 to +4, 6 fold cations = Medium, +2 to +4, 6 fold cations ZZ = Small, = Small, ≥ +3≥ +3, strong 4 fold cations, strong 4 fold cations WW = Other anions: (OH) = Other anions: (OH)--, F, F--, Cl, Cl--,(SO,(SO44))-2-2,(CO ,(CO 33))

-2-2

p/q depends on polyhedral polymerizationp/q depends on polyhedral polymerization m, n & r depend on valence & neutralitym, n & r depend on valence & neutrality

Nesosilicates: Olivine GroupNesosilicates: Olivine Group Ordinary Olivine series: OrthorhombicOrdinary Olivine series: Orthorhombic

Forsterite: MgForsterite: Mg22SiOSiO44

Fayalite: FeFayalite: Fe22SiOSiO44

Liebenbergite: (Ni,Mg)Liebenbergite: (Ni,Mg)22SiOSiO44

Tephroite: MnTephroite: Mn22SiOSiO44

Monticellite: CaMgSiOMonticellite: CaMgSiO44

Kirschsteinite: CaFeSiOKirschsteinite: CaFeSiO44

Glaucochroite: CaMnSiOGlaucochroite: CaMnSiO44

Forsterite FayaliteForsterite FayaliteMonticellite GlaucochroiteMonticellite Glaucochroite

Olivine Structure projected on (100)Olivine Structure projected on (100)Octahedra: M2 is ~regular M1 distortedOctahedra: M2 is ~regular M1 distorted(Mg,Fe,Ni)2SiO4

M1 vs M2 Thermometer

M1 distortion = F (Temperature)

Nesosilicates: Garnet GroupNesosilicates: Garnet Group Pyralspite series:Pyralspite series:

Pyrope:Pyrope: MgMg3 3 AlAl22 SiSi33 O O1212

Almandine:Almandine: FeFe3 3 AlAl22 SiSi33 O O1212

Spessartine: MnSpessartine: Mn33 AlAl22 SiSi33 O O1212

Ugrandite series:Ugrandite series: Uvarovite:Uvarovite: CaCa33 CrCr2 2 SiSi33 O O1212

Grossularite:Grossularite: CaCa33 AlAl22 SiSi33 O O1212

Andradite:Andradite: CaCa3 3 FeFe+3+32 2 SiSi33 O O1212

Almandine-Australia Spessartine-AustraliaAlmandine-Australia Spessartine-Australia

Uvarovite-Finland Andradite-AfghanistanUvarovite-Finland Andradite-Afghanistan

Garnet Structure on [001]Garnet Structure on [001]Lone Tetrahedra, Octahedra & Distorted CubesLone Tetrahedra, Octahedra & Distorted Cubes

Aluminosilicate GroupAluminosilicate Group AlAl22 SiOSiO5 5 (mostly orthorhombic) PT indicators (mostly orthorhombic) PT indicators

Andalusite: moderate P/T meta-rocksAndalusite: moderate P/T meta-rocks• ½ Al in octahedral chains, ½ as Al-5fold/Si-4 chains½ Al in octahedral chains, ½ as Al-5fold/Si-4 chains

Kyanite (Triclinic): Hi P/T meta-rocksKyanite (Triclinic): Hi P/T meta-rocks• All Al is octahedral in chains || to C or lone octahedraAll Al is octahedral in chains || to C or lone octahedra

Sillimanite: Hi T/P meta-rocksSillimanite: Hi T/P meta-rocks• Octahedral Al chains & || tetrahedral chains Al/Si/Al/Si..Octahedral Al chains & || tetrahedral chains Al/Si/Al/Si..

Mullite: Very High T contact metaMullite: Very High T contact meta• AlAl88 ((Si,Al)O ((Si,Al)O44) ) 4 4 (O,OH,F) (O,OH,F)

Kyanite on [001]Kyanite on [001]edge sharing octahedra II to cedge sharing octahedra II to c

Andalusite var. ChiastoliteAndalusite var. Chiastolite

Kyanite (below)Kyanite (below)

Sillimanite var. FibroliteSillimanite var. Fibrolite

Sillimanite (left) & Andalusite (right)Sillimanite (left) & Andalusite (right)

[Al][Al]VIVI & [Al-Si] & [Al-Si]IVIV chains II to c chains II to c

Mullite: Isle of MullMullite: Isle of MullEifel (S.Wolfsreid), Rotorua (M.leGras)Eifel (S.Wolfsreid), Rotorua (M.leGras)

Sorosilicate “anion-dimer”Sorosilicate “anion-dimer”

Sorosilicate GroupSorosilicate Group• Ions in Ca site Ions in Ca site Ions in Al site (non-chain)Ions in Al site (non-chain)

EpidoteEpidote CaCa AlAl ClinozoisiteClinozoisite CaCa FeFe+3+3 , Al , Al PiedmontitePiedmontite CaCa MnMn+3+3, Fe, Fe+3+3, Al, Al Allanite:Allanite: Na, Ca, Ce, LaNa, Ca, Ce, La Mg Fe Mg Fe+2+2 Fe Fe+3+3 Al Al

ZoisiteZoisite CaCa FeFe+3+3 , Al , Al

Epidote unit cell on [010]Epidote unit cell on [010]

Epidote versus ZoisiteEpidote versus Zoisite(Monoclinic vs Orthorhombic)(Monoclinic vs Orthorhombic)

Allanite-BlackAllanite-BlackZoisite var Thulite-Zoisite var Thulite-

pinkpinkEpidote-GreenEpidote-Green

Tanzanite-3chroicTanzanite-3chroic

Benitoite

Papagoite

Beryl & Tourmaline

CyclosilicatesCyclosilicates

6 member Cyclosilicate Group6 member Cyclosilicate Group

Beryl:Beryl: Borosilicate with up to 7 different ions or vacancies!Borosilicate with up to 7 different ions or vacancies!

Tourmaline:Tourmaline: Borosilicate with up to 7 different ions or vacancies!Borosilicate with up to 7 different ions or vacancies!

CordieriteCordierite

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

Emerald & Aquamarine

Beryl: Beryl: Aquamarine, Emerald, MorganiteAquamarine, Emerald, Morganite

Low Cordierite’s Al-Si backboneLow Cordierite’s Al-Si backboneOrthorhombic, pseudo-hexagonalOrthorhombic, pseudo-hexagonal

High Cordierite: IndialiteIs Hexagonal

CordieriteCordieriteRed Trilings & Blue on QuartzRed Trilings & Blue on Quartz

Tourmaline End Members & Tourmaline End Members & Substitutions-Site OccupanciesSubstitutions-Site Occupancies

Tourmaline a (0001) & b C verticalTourmaline a (0001) & b C vertical

Tourmaline: ElbaiteTourmaline: ElbaiteDraviteDravite

PyroxenePyroxene

WollastoniteWollastonite

RhodoniteRhodonite

PyroxmangitePyroxmangite

Pyroxene Ca-Mg-Fe Pyroxene Ca-Mg-Fe Classification Classification

TrianglesTriangles

Chain Silicates:Chain Silicates:Cation Sites & SubstitutionsCation Sites & Substitutions

(SiO(SiO33))-2-2 Single Chain Polymer Single Chain Polymer

Jadeite NaAl(SiOJadeite NaAl(SiO33))22 Structure on [100] Structure on [100]

JadeiteJadeite

Monoclinic PyroxeneMonoclinic Pyroxeneprojected onto [001]projected onto [001]

Unit Cells of Enstatite & DiopsideUnit Cells of Enstatite & Diopsideprojected on [010]projected on [010]

Who has the larger unit cell & mirror plane?Could pyroxenes exhibit exsolution? Why or not?

Orthorhombic

Monoclinic

Amphibole Compositions in the Amphibole Compositions in the Ca-Mg-Fe TriangleCa-Mg-Fe Triangle

Orthorhombic

Monoclinic

HypotheticalEnd member

Orthorhombic

Anthophyllite

GruneriteVar. Amosite

Actinolite

                                                                                                                                                                                                                                                                                                                                                            

Ferro-Actinolite

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

Chain Silicates:Chain Silicates:Cation Sites & SubstitutionsCation Sites & Substitutions

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

Intergrowth of 2 polymorphs of:Intergrowth of 2 polymorphs of:NaNa0.10.1FeFe2.22.2MgMg4.54.5AlAl0.10.1SiSi88OO2222(OH)(OH)22

Orthorhombic

MonoclinicTremolite

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 Biopyriboles” Mixing single, double and triple chain repeatsand 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 Biopyriboles” Mixing single, double and triple chain repeatsand triple chain repeats

AenigmatiteRepeats groups of 4 single chains

Aenigmatite: Aenigmatite:

NaNa22FeFe55TiSiTiSi66OO1818OO22

TriclinicTriclinic

Striated blades: Striated blades: Grey, Black, Grey, Black,

BronzeBronze

G. FrettiG. FrettiSan Miguel San Miguel

AzoresAzores

Phyllosilicates (Micas & Clays)Phyllosilicates (Micas & Clays)

Undistorted Hexagonal Ring in an Si2O5 sheet(Triangles in tetrahedra = triangles in octahedra)

““Infinite” Octahedral sheetInfinite” Octahedral sheetAll Octahedra rest on triangular facesAll Octahedra rest on triangular faces

XO6 octahedra, other transition metals substitute

Kaolinite T/O Structure & Pigg’s EggKaolinite T/O Structure & Pigg’s Egg((pseudomorph after orthoclase, Cornwall)pseudomorph after orthoclase, Cornwall)

Al2 Si2O5 (OH)4 Triclinic (pseudo-hexagonal)

(due to T/O stack) Named for Gao-Ling, China

Muscovite Muscovite KAl2 [AlSi3O10] (OH)2(Plan View) Octahedral Sheet smaller, Tetrahedra (Plan View) Octahedral Sheet smaller, Tetrahedra

rotaterotateOpposed rotations of adjacent tetrahedra makes this sheet TrigonalSlight 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 (T-O-T-I… Muscovite (T-O-T-I… Structure)Structure)

Where is the cleavage? What bond type?Where is the cleavage? What bond type?

i

K [ ]Al2 [AlSi3O10] (OH)2

Muscovite is aDioctahedral mica

(2 of every 3 sites have Al)

[Vacant]

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

2M & 3T Polytypes in Micas2M & 3T Polytypes in Micasarise from (OH)/Hex stacking rotationsarise from (OH)/Hex stacking rotations

10, 20 & 30 Angstrom Stacking10, 20 & 30 Angstrom Stackingof Mica Polytypes – Clays & Soilsof Mica Polytypes – Clays & Soils

Pyrophyllite T-O-T Layer “Fire-leaf”Pyrophyllite T-O-T Layer “Fire-leaf”

Al2 Si4O10 (OH)2 Monoclinic (due to stack)

Hydrothermal veins & schists, Belgium

Trioctahedral Micas Trioctahedral Micas have 3/3 of the have 3/3 of the

Octahedral sites Octahedral sites filled.filled.

Dioctahedral Micas Dioctahedral Micas have 2/3 of the have 2/3 of the

Octahedral sites Octahedral sites filled.filled.

Which are Biotite & Chlorite?Which are Biotite & Chlorite?

MgAl

Chlorite Group: (T-O-T)-I-(T-O-T) Chlorite Group: (T-O-T)-I-(T-O-T) 12 Triclinic or Monoclinic Structures 12 Triclinic or Monoclinic Structures

The general formula may be stated: A5-6T4Z18 .

A = Al, Fe+2, Fe+3, Li, Mg, Mn, or NiT = 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)-2HVermiculite: (T-O-T)-2H22O-(T-O-T)O-(T-O-T)

(Mg,)3 (Al, Si)4 O10 (OH)2 – 4.5 H2O (Mg)0.35

-

Monoclinic

ExchangeableCations

Serpentine:Serpentine: Crysotile vs. AntigoriteCrysotile vs. Antigorite

(Mg,Fe+2)3 Si2O5 (OH)4

Monoclinic

Partial bendingAccomodates misfit

of T-O Layers

2 different Polytypes for Serpentine2 different Polytypes for Serpentine from stacking offsets of T-O sheets from stacking offsets of T-O sheets

a) Alpha – High Quartz on (0001)4 unit cells with 62 screw axes

Fractional heights noted on tetrahedra

b) Beta – Low Quartz4 unit cells with 32 screw axesFractional heights noted on tetrahedra

Structures of SiOStructures of SiO22 Polymorphs PolymorphsBeta Quartz, Chalcedony, AgateBeta Quartz, Chalcedony, Agate

Structures of SiOStructures of SiO22 Polymorphs Polymorphs

a Tridymite (0001)Eifel

b Cristobalite (111)Italy

c Coesite (001)Behringer, AZ

d Stishovite (100)Bisbee, AZ

P-T Phase Diagram for SiOP-T Phase Diagram for SiO22

Polymorphs (Where would these form?)Polymorphs (Where would these form?)

Feldspars: Compositions & Feldspars: Compositions & Classification of Hi T PhasesClassification of Hi T Phases

Hi Sanidine on (Hi Sanidine on (2201)01)

4-Membered Tetrahedral Chains4-Membered Tetrahedral ChainsParallel to a axis in FeldsparsParallel to a axis in Feldspars

SiSi44OO88 Framework Framework (Na,K)(AlSi (Na,K)(AlSi33 O O88) or Ca(Al) or Ca(Al22 Si Si22OO88)) 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 FeldsparsMiscibility Gap for Alkali Feldsparsat T < 650°C, Leucite can’t exist in plutonsat T < 650°C, Leucite can’t exist in plutons

Possible Cooling Paths and Phase Possible Cooling Paths and Phase changes for Hi Sanidinechanges for Hi Sanidine

Experimental Solid Solution in Or-Ab-AnExperimental Solid Solution in Or-Ab-An

Plagioclase Feldspar Phase DiagramPlagioclase Feldspar Phase DiagramAlmost complete solid solution, miscibilityAlmost complete solid solution, miscibility

Or-Ab-An versus TemperatureOr-Ab-An versus TemperatureThermal topology of the feldspar systemThermal topology of the feldspar system

Solvus Solvi

Cotectic trough

Bow

en’s

Con

tinuo

us

Rea

ctio

n S

erie

s

Feldspathoids:Feldspathoids:Silica Undersaturated TectosilicatesSilica Undersaturated Tectosilicates

Leucite Structure down [001], c axisLeucite Structure down [001], c axis

Nepheline Kalsilite Structure on (0001)Nepheline Kalsilite Structure on (0001)There are 4 distinct tetrahedral sites.There are 4 distinct tetrahedral sites.

Sodalite NaSodalite Na22(AlSiO(AlSiO44))66ClCl22

Hackmanite,Nosean, Hauyne Hackmanite,Nosean, Hauyne

Chains of Tetrahedra in Fibrous Chains of Tetrahedra in Fibrous Zeolites Zeolites Natrolite NaNatrolite Na22AlAl22SiSi33OO1010 2H 2H22OO

Chabazite: Chabazite: CaCa22AlAl22SiSi44OO1212 6H 6H22OO

open channels for water, ion exchangeopen channels for water, ion exchange

Thermal Thermal Gravimetric Curves Gravimetric Curves

fro water loss on fro water loss on heating.heating.

This is reversible This is reversible unlike loss of unlike loss of

hydrogen or OH hydrogen or OH groups from other groups from other

silicates.silicates.

Zeolite Molecular Sieve can separateZeolite Molecular Sieve can separaten-alkanes from branched iso-alkanesn-alkanes from branched iso-alkanes

Ion exchange properties allows a Ion exchange properties allows a strong solution of one cation to displace strong solution of one cation to displace

another.another.

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

occurrence!occurrence!