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Minerlaogi II
Average Composition of the Continental Crust
Weight Percent Volume Percent
SiO
O
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]
Silicates are classified on the basis of Si-O polymerism
[SiO3]2- single chains Inosilicates [Si4O11]4- Double tetrahedra
pyroxenes pyroxenoids amphiboles
Silicates are classified on the basis of Si-O polymerism
[Si2O5]2- Sheets of tetrahedra Phyllosilicates
micas talc clay minerals serpentine
Silicates are classified on the basis of Si-O polymerism
[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
bb
cc
projectionprojection
Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2
bb
cc
perspectiveperspective
Nesosilicates: independent SiO4 tetrahedra
Olivine (001) view blue = M1 yellow = M2Olivine (001) view blue = M1 yellow = M2
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
bb
aa
Nesosilicates: independent SiO4 tetrahedra
Nesosilicates: independent SiO4 tetrahedra
Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2
bb
cc
M1 and M2 as polyhedraM1 and M2 as polyhedra
Nesosilicates: independent SiO4 tetrahedra
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
Nesosilicates: independent SiO4 tetrahedra
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
Nesosilicates: independent SiO4 tetrahedra
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
aa11
aa22
aa33
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]]
bb
a si
na
sin
Where are the Si-O-Si-O chains??Where are the Si-O-Si-O chains??
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)
bb
a si
na
sin
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)
bb
a si
na
sin
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)
bb
a si
na
sin
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)
bb
a si
na
sin
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)
bb
a si
na
sin
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)
Perspective viewPerspective view
Inosilicates: single chains- pyroxenes
TT
M1M1
TT
Creates an “I-beam” Creates an “I-beam” like unit in the like unit in the
structure.structure.
Inosilicates: single chains- pyroxenes
TT
M1M1
TT
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
(+)(+)
(+)(+)(+)(+)
(+)(+)(+)(+)
Inosilicates: single chains- pyroxenes
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
(+)(+)
(+)(+)(+)(+)
Inosilicates: single chains- pyroxenes
(+)(+)(+)(+)
Pyroxene Chemistry
The general pyroxene formula:
W1-P (X,Y)1+P Z2O6
Where
– 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
bb
a si
na
sin
Inosilicates: double chains- amphiboles
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
bb
a si
na
sin
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
Inosilicates: double chains- amphiboles
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)
Inosilicates: double chains- amphiboles
bb
a si
na
sin
(+)(+) (+)(+)
(+)(+)
(+)(+)
(+)(+)
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
aa
bb
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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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
cc
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
aa11
aa22
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
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
Yellow = (OH)Yellow = (OH)
T T O O -- T T O O -- T T OO
vdwvdw
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
vdwvdw
weak van der Waals bonds between T - O - T groups weak van der Waals bonds between T - O - T groups
Yellow = (OH)Yellow = (OH)
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
vdwvdw
weak van der Waals bonds between T - O - T groups weak van der Waals bonds between T - O - T groups
Yellow = (OH)Yellow = (OH)
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 13.84 Klein and Hurlbut Manual of Mineralogy, © John Wiley & Sons
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”
Cover of Science, October 28, 1977 © AAAS
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
Fig. 6, Veblen et al (1977) Science 198 © AAAS
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)
“Biopyriboles”Fig. 7, Veblen et al (1977) Science 198 © AAAS
Tectosilicates
Stishovite
Coesite
α- quartz
- quartz
Liquid
TridymiteCristobalite
600 1000 1400 1800 2200 2600
2
4
6
8
10
( )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
TridymiteCristobalite
Tectosilicates
High Quartz at 581oC
001 Projection Crystal Class 622001 Projection Crystal Class 622
Stishovite
Coesite
α- quartz
- quartz
Liquid
TridymiteCristobalite
Tectosilicates
Cristobalite
001 Projection Cubic Structure001 Projection Cubic Structure
Stishovite
Coesite
α- quartz
- quartz
Liquid
TridymiteCristobalite
Tectosilicates
Stishovite
High pressure High pressure Si SiVIVI
Stishovite
Coesite
α- quartz
- quartz
Liquid
TridymiteCristobalite
Tectosilicates
Low Quartz Stishovite
SiSiIVIV Si SiVIVI
Quartz structure
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Fig.
3.27
BandedAgate
Fig. 3.28
GreenFeldspar
Feltspat
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Ortoklas/Mikroklin
Albitt Anortitt
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Avblanding av feltspat ved avkjøling
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Plagioklas
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Kalifeltspat (mikroklin)
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