Minerlaogi II Average Composition of the Continental Crust Weight PercentVolume Percent Si O O Table...

Minerlaogi II

Average Composition of the Continental Crust

Weight Percent Volume Percent

Table 3.4

Fig. 3.8

Ionic Radii of some

geologically important ions

Silika Tetraederet

Silicates are classified on the basis of Si-O polymerism

[SiO4]4- Independent tetrahedra Nesosilicates

Examples: olivine garnet

[Si2O7]6- Double tetrahedra Sorosilicates

Examples: epidote

n[SiO3]2- n = 3, 4, 6 Cyclosilicates

Examples: benitoite BaTi[Si3O9]

axinite Ca3Al2BO3[Si4O12]OH

beryl Be3Al2[Si6O18]

[SiO3]2- single chains Inosilicates [Si4O11]4- Double tetrahedra

pyroxenes pyroxenoids amphiboles

[Si2O5]2- Sheets of tetrahedra Phyllosilicates

micas talc clay minerals serpentine

[SiO2] 3-D frameworks of tetrahedra: fully polymerized Tectosilicates

quartz and the silica minerals feldspars feldspathoids zeolites

low-quartzlow-quartz

Olivine:

formed from single silica tetrahedra

Forsterite Mg2SiO4Fayalite Fe2SiO4

Peridot - gem quality olivine

This is a cut crystal

An olivine nodule in a volcanic rock

Olivine picture gallery

Nesosilicates: independent SiO4 tetrahedra

Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2

projectionprojection

perspectiveperspective

M1 in rows M1 in rows and share and share edgesedges

M2 form M2 form layers in a-c layers in a-c that share that share corners corners

Some M2 and Some M2 and M1 share M1 share edgesedges

M1 and M2 as polyhedraM1 and M2 as polyhedra

Olivine Occurrences:– Principally in mafic and ultramafic igneous and meta-igneous rocks – Fayalite in meta-ironstones and in some alkalic granitoids

– Forsterite in some siliceous dolomitic marbles

Monticellite CaMgSiO4 Ca M2 (larger ion, larger site)

High grade metamorphic siliceous carbonates

The garnet picture gallery

Garnet (001) view blue = Si purple = B turquoise = AGarnet (001) view blue = Si purple = B turquoise = A

Garnet: AGarnet: A2+2+33 B B3+3+

22 [SiO [SiO44]]3 3

““Pyralspites”Pyralspites” - B = Al - B = AlPyPyrope: Mgrope: Mg33 Al Al22 [SiO [SiO44]]3 3

AlAlmandine: Femandine: Fe33 Al Al22 [SiO [SiO44]]33

SpSpessartine: Mnessartine: Mn33 Al Al22 [SiO [SiO44]]33

““Ugrandites”Ugrandites” - A = Ca - A = CaUUvarovite: Cavarovite: Ca33 Cr Cr22 [SiO [SiO44]]33

GrGrossularite: Caossularite: Ca33 Al Al22 [SiO [SiO44]]33

AndAndradite: Caradite: Ca33 Fe Fe22 [SiO [SiO44]]33

Occurrence:Occurrence:Mostly metamorphicMostly metamorphicSome high-Al igneousSome high-Al igneousAlso in some mantle peridotitesAlso in some mantle peridotites

Garnet (001) view blue = Si purple = A turquoise = BGarnet (001) view blue = Si purple = A turquoise = B

Garnet: AGarnet: A2+2+33 B B3+3+

22 [SiO [SiO44]]3 3

““Pyralspites”Pyralspites” - B = Al - B = AlPyPyrope: Mgrope: Mg33 Al Al22 [SiO [SiO44]]3 3

AlAlmandine: Femandine: Fe33 Al Al22 [SiO [SiO44]]33

SpSpessartine: Mnessartine: Mn33 Al Al22 [SiO [SiO44]]33

““Ugrandites”Ugrandites” - A = Ca - A = CaUUvarovite: Cavarovite: Ca33 Cr Cr22 [SiO [SiO44]]33

GrGrossularite: Caossularite: Ca33 Al Al22 [SiO [SiO44]]33

AndAndradite: Caradite: Ca33 Fe Fe22 [SiO [SiO44]]33

Occurrence:Occurrence:Mostly metamorphicMostly metamorphic

Pyralspites in meta-shalesPyralspites in meta-shalesUgrandites in meta-carbonatesUgrandites in meta-carbonates

Some high-Al igneousSome high-Al igneousAlso in some mantle peridotitesAlso in some mantle peridotites

Fig. 3.20

Linking Silicate Tetrahedra

Chains (polymers) of silicate anions

Enkeltkjeder - eks. Diopside (en pyroxen-CaMgSi2O6)

Inosilicates: single chains- pyroxenes

Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)

Diopside: CaMg [SiDiopside: CaMg [Si22OO66]]

Where are the Si-O-Si-O chains??Where are the Si-O-Si-O chains??

Perspective viewPerspective view

Creates an “I-beam” Creates an “I-beam” like unit in the like unit in the

structure.structure.

Creates an “I-beam” Creates an “I-beam” like unit in the like unit in the

structurestructure

(+)(+)

The pyroxene The pyroxene structure is then structure is then

composed of composed of alternating I-beamsalternating I-beams

Clinopyroxenes have Clinopyroxenes have all I-beams oriented all I-beams oriented the same: all are (+) the same: all are (+) in this orientation in this orientation

(+)(+)

(+)(+)(+)(+)

Note that M1 sites are Note that M1 sites are smaller than M2 sites, since smaller than M2 sites, since they are at the apices of the they are at the apices of the

tetrahedral chainstetrahedral chains

The pyroxene The pyroxene structure is then structure is then

composed of composed of alternation I-beamsalternation I-beams

Clinopyroxenes have Clinopyroxenes have all I-beams oriented all I-beams oriented the same: all are (+) the same: all are (+) in this orientation in this orientation

(+)(+)

(+)(+)(+)(+)

Pyroxene Chemistry

The general pyroxene formula:

W1-P (X,Y)1+P Z2O6

– W = Ca Na

– X = Mg Fe2+ Mn Ni Li

– Y = Al Fe3+ Cr Ti

– Z = Si Al

Anhydrous so high-temperature or dry conditions favor pyroxenes over amphiboles

Pyroxene ChemistryThe pyroxene quadrilateral and opx-cpx solvus

Coexisting opx + cpx in many rocks (pigeonite only in volcanics)

DiopsideDiopside HedenbergiteHedenbergite

WollastoniteWollastonite

EnstatiteEnstatite FerrosiliteFerrosiliteorthopyroxenes

clinopyroxenes

pigeonite (Mg,Fe)(Mg,Fe)22SiSi22OO66 Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO66

pigeonite clinopyroxenes

orthopyroxenes

SolvusSolvus

12001200ooCC

10001000ooCC

800800ooCC

Pyroxene Chemistry

“Non-quad” pyroxenesJadeiteJadeite

NaAlSiNaAlSi22OO66

Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO66

AegirineAegirine

NaFeNaFe3+3+SiSi22OO66

Diopside-HedenbergiteDiopside-Hedenbergite

Ca-Tschermack’s Ca-Tschermack’s moleculemolecule CaAl2SiOCaAl2SiO66

Ca / (Ca + Na)Ca / (Ca + Na)

0.20.2

0.80.8

Omphaciteaegirine- augite

AugiteAugite

Spodumene: Spodumene: LiAlSiLiAlSi22OO66

Inosilicates: double chains- amphiboles

Tremolite (001) view blue = Si purple = M1 rose = M2 gray = M3 (all Mg)Tremolite (001) view blue = Si purple = M1 rose = M2 gray = M3 (all Mg)yellow = M4 (Ca)yellow = M4 (Ca)

Tremolite:Tremolite:CaCa22MgMg55 [Si [Si88OO2222] (OH)] (OH)22

Hornblende:Hornblende:(Ca, Na)(Ca, Na)2-3 2-3 (Mg, Fe, Al) (Mg, Fe, Al)55

[(Si,Al)[(Si,Al)88OO2222] (OH)] (OH)22

Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 light blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purple ball = A (Na)light blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purple ball = A (Na)

little turquoise ball = Hlittle turquoise ball = H

Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 light blue = M3 (all Mg, Fe)light blue = M3 (all Mg, Fe)

Hornblende:Hornblende:(Ca, Na)(Ca, Na)2-3 2-3 (Mg, Fe, (Mg, Fe,

Al)Al)55 [(Si,Al) [(Si,Al)88OO2222] (OH)] (OH)22

Same I-beam Same I-beam architecture, but architecture, but the I-beams are the I-beams are fatter (double fatter (double

chains)chains)

(+)(+) (+)(+)

(+)(+)

Same I-beam Same I-beam architecture, but architecture, but the I-beams are the I-beams are fatter (double fatter (double

chains)chains)

All are (+) on All are (+) on clinoamphiboles clinoamphiboles and alternate in and alternate in

orthoamphibolesorthoamphiboles

Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 light blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purple ball = A (Na)light blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purple ball = A (Na)

little turquoise ball = Hlittle turquoise ball = H

Hornblende:Hornblende:(Ca, Na)(Ca, Na)2-3 2-3 (Mg, Fe, (Mg, Fe,

Al)Al)55 [(Si,Al) [(Si,Al)88OO2222] (OH)] (OH)22

Inosilicates

Cleavage angles can be interpreted in terms of weak bonds in M2 sites (around I-beams instead of through them)

Narrow single-chain I-beams 90o cleavages in pyroxenes while wider double-chain I-beams 60-120o cleavages in amphiboles

pyroxenepyroxene amphiboleamphibole

Cleavage in the Chain

Silicates

Fig. 3.24

Pyroxene

Amphibole

See handout for more information

General formula:

W0-1 X2 Y5 [Z8O22] (OH, F, Cl)2

W = Na K

X = Ca Na Mg Fe2+ (Mn Li)

Y = Mg Fe2+ Mn Al Fe3+ Ti

Z = Si Al

Again, the great variety of sites and sizes a great chemical range, and hence a broad stability range

The hydrous nature implies an upper temperature stability limit

Amphibole Chemistry

Ca-Mg-Fe Amphibole “quadrilateral” (good analogy with pyroxenes)

Amphibole Chemistry

Al and Na tend to stabilize the orthorhombic form in low-Ca amphiboles, so anthophyllite gedrite orthorhombic series extends to Fe-rich gedrite in more Na-Al-rich compositions

TremoliteTremoliteCaCa22MgMg55SiSi88OO2222(OH)(OH)22

FerroactinoliteFerroactinoliteCaCa22FeFe55SiSi88OO2222(OH)(OH)22

AnthophylliteAnthophyllite

MgMg77SiSi88OO2222(OH)(OH)22FeFe77SiSi88OO2222(OH)(OH)22

Actinolite

Cummingtonite-grunerite

OrthoamphibolesOrthoamphiboles

ClinoamphibolesClinoamphiboles

Hornblende has Al in the tetrahedral site

Geologists traditionally use the term “hornblende” as a catch-all term for practically any dark amphibole. Now the common use of the microprobe has petrologists casting “hornblende” into end-member compositions and naming amphiboles after a well-represented end-member.

Sodic amphiboles

Glaucophane: Na2 Mg3 Al2 [Si8O22] (OH)2

Riebeckite: Na2 Fe2+3 Fe3+

2 [Si8O22] (OH)2

Sodic amphiboles are commonly blue, and often called “blue amphiboles”

Amphibole Chemistry

Tremolite (Ca-Mg) occurs in meta-carbonates

Actinolite occurs in low-grade metamorphosed basic igneous rocks

Orthoamphiboles and cummingtonite-grunerite (all Ca-free, Mg-Fe-rich amphiboles) are metamorphic and occur in meta-ultrabasic rocks and some meta-sediments. The Fe-rich grunerite occurs in meta-ironstones

The complex solid solution called hornblende occurs in a broad variety of both igenous and metamorphic rocks

Sodic amphiboles are predominantly metamorphic where they are characteristic of high P/T subduction-zone metamorphism (commonly called “blueschist” in reference to the predominant blue sodic amphiboles

Riebeckite occurs commonly in sodic granitoid rocks

Amphibole Occurrences

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kreves for å se dette bildet.

SiO4 tetrahedra polymerized into 2-D sheets: [Si2O5]

Apical O’s are unpolymerized and are bonded to other constituents

Phyllosilicates

Tetrahedral layers are bonded to octahedral layers

(OH) pairs are located in center of T rings where no apical O

Phyllosilicates

Octahedral layers can be understood by analogy with hydroxides

Phyllosilicates

Brucite: Mg(OH)Brucite: Mg(OH)22

Layers of octahedral Mg in Layers of octahedral Mg in coordination with (OH)coordination with (OH)

Large spacing along Large spacing along cc due due to weak van der waals to weak van der waals bondsbonds

Phyllosilicates

Gibbsite: Al(OH)Gibbsite: Al(OH)33

Layers of octahedral Al in coordination with (OH)Layers of octahedral Al in coordination with (OH)

AlAl3+3+ means that means that only 2/3 of the VI sites may be occupiedonly 2/3 of the VI sites may be occupied for charge-balance reasons for charge-balance reasons

Brucite-type layers may be called Brucite-type layers may be called trioctahedraltrioctahedral and gibbsite-type and gibbsite-type dioctahedraldioctahedral

Phyllosilicates

Kaolinite:Kaolinite: Al Al22 [Si [Si22OO55] (OH)] (OH)44

T-layers and T-layers and didiocathedral (Alocathedral (Al3+3+) layers ) layers

(OH) at center of T-rings and fill base of VI layer (OH) at center of T-rings and fill base of VI layer

Yellow = (OH)Yellow = (OH)

T T O O -- T T O O -- T T OO

vdwvdw

weak van der Waals bonds between T-O groups weak van der Waals bonds between T-O groups

Phyllosilicates

Serpentine:Serpentine: Mg Mg33 [Si [Si22OO55] (OH)] (OH)44

T-layers and T-layers and tritriocathedral (Mgocathedral (Mg2+2+) layers ) layers

(OH) at center of T-rings and fill base of VI layer (OH) at center of T-rings and fill base of VI layer

T T O O -- T T O O -- T T OO

vdwvdw

weak van der Waals bonds between T-O groups weak van der Waals bonds between T-O groups

Serpentine

Octahedra are a bit larger than tetrahedral Octahedra are a bit larger than tetrahedral match, so they cause bending of the T-O match, so they cause bending of the T-O layers (after Klein and Hurlbut, 1999).layers (after Klein and Hurlbut, 1999).

Antigorite maintains a Antigorite maintains a sheet-like form by sheet-like form by

alternating segments of alternating segments of opposite curvatureopposite curvature

Chrysotile does not do this Chrysotile does not do this and tends to roll into tubesand tends to roll into tubes

Serpentine

The rolled tubes in chrysotile resolves the apparent The rolled tubes in chrysotile resolves the apparent paradox of asbestosform sheet silicatesparadox of asbestosform sheet silicates

S = serpentine T = talcS = serpentine T = talcNagby and Faust (1956) Am. Mineralogist 41, 817-836.

Veblen and Busek, 1979, Science 206, 1398-1400.

Phyllosilicates

Pyrophyllite:Pyrophyllite: Al Al22 [Si [Si44OO1010] (OH)] (OH)22

T-layer - T-layer - didiocathedral (Alocathedral (Al3+3+) layer - T-layer ) layer - T-layer

T T O O T T -- T T O O T T -- T T O O TT

vdwvdw

weak van der Waals bonds between T - O - T groups weak van der Waals bonds between T - O - T groups

Phyllosilicates

Talc:Talc: Mg Mg33 [Si [Si44OO1010] (OH)] (OH)22

T-layer - T-layer - tritriocathedral (Mgocathedral (Mg2+2+) layer - T-layer ) layer - T-layer

T T O O T T -- T T O O T T -- T T O O TT

vdwvdw

weak van der Waals bonds between T - O - T groups weak van der Waals bonds between T - O - T groups

Phyllosilicates

Muscovite:Muscovite: KK Al Al22 [Si [Si33AlAlOO1010] (OH)] (OH)2 2 (coupled K - Al(coupled K - AlIVIV))

T-layer - T-layer - didiocathedral (Alocathedral (Al3+3+) layer - T-layer - ) layer - T-layer - KK

T T O O T T KK T T O O T T KK T T O O TT

K between T - O - T groups is stronger than vdwK between T - O - T groups is stronger than vdw

Phyllosilicates

Phlogopite:Phlogopite: K Mg K Mg33 [Si [Si33AlOAlO1010] (OH)] (OH)22

T-layer - T-layer - tritriocathedral (Mgocathedral (Mg2+2+) layer - T-layer - ) layer - T-layer - KK

T T O O T T KK T T O O T T KK T T O O TT

K between T - O - T groups is stronger than vdwK between T - O - T groups is stronger than vdw

A Summary of

Phyllosilicate Structures

Phyllosilicates

Fig. 3.25

Clay: a sheet silicate

Chlorite: (Mg, Fe)3 [(Si, Al)4O10] (OH)2 (Mg, Fe)3 (OH)6

= T - O - T - (brucite) - T - O - T - (brucite) - T - O - T -

Very hydrated (OH)8, so low-temperature stability (low-T metamorphism and alteration of mafics as cool)

Phyllosilicates

Why are there single-chain-, double-chain-, and sheet-polymer types, and not triple chains, quadruple chains, etc??

“Biopyriboles”

It turns out that there are some intermediate types, predicted by J.B. Thompson and discovered in 1977 Veblen, Buseck, and Burnham

Cover of Science: anthophyllite (yellow) reacted to form chesterite (blue & green) and jimthompsonite (red)

Streaked areas are highly disordered

“Biopyriboles”

HRTEM image of anthophyllite (left) with typical double-chain width

Jimthompsonite (center) has triple-chains

Chesterite is an ordered alternation of double- and triple-chains

anthophylliteanthophyllite jimthompsonitejimthompsonite chesteritechesterite

Disordered structures show 4-chain widths and even a 7-chain width

Obscures the distinction between pyroxenes, amphiboles, and micas (hence the term biopyriboles: biotite-pyroxene-amphibole)

Tectosilicates

Stishovite

Coesite

α- quartz

- quartz

Liquid

TridymiteCristobalite

600 1000 1400 1800 2200 2600

( )Pressure GPa

TemperatureoC

After Swamy and Saxena (1994) J. Geophys. Res., 99, 11,787-11,794.

Tectosilicates

Low Quartz

001 Projection Crystal Class 32001 Projection Crystal Class 32

Stishovite

Coesite

α- quartz

- quartz

Liquid

Tectosilicates

High Quartz at 581oC

001 Projection Crystal Class 622001 Projection Crystal Class 622

Stishovite

Coesite

α- quartz

- quartz

Liquid

Tectosilicates

Cristobalite

001 Projection Cubic Structure001 Projection Cubic Structure

Stishovite

Coesite

α- quartz

- quartz

Liquid

Tectosilicates

Stishovite

High pressure High pressure Si SiVIVI

Stishovite

Coesite

α- quartz

- quartz

Liquid

Tectosilicates

Low Quartz Stishovite

SiSiIVIV Si SiVIVI

Quartz structure

BandedAgate

Fig. 3.28

GreenFeldspar

Feltspat

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Ortoklas/Mikroklin

Albitt Anortitt

Avblanding av feltspat ved avkjøling

Plagioklas

Kalifeltspat (mikroklin)

Minerlaogi II Average Composition of the Continental Crust Weight PercentVolume Percent Si O O Table...

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