Mineral Structures Mineral Structures Silicates are classified on the Silicates are classified on the basis of Si-O polymerism basis of Si-O polymerism The culprit: the [SiO The culprit: the [SiO 4 ] ] 4- 4- tetrahedron tetrahedron
Mineral StructuresMineral StructuresSilicates are classified on the basis of Si-O polymerism Silicates are classified on the basis of Si-O polymerism
The culprit: the [SiOThe culprit: the [SiO44]]4-4- tetrahedron tetrahedron
Mineral StructuresMineral StructuresSilicates are classified on the basis of Si-O polymerism Silicates are classified on the basis of Si-O polymerism
[SiO[SiO44]]4-4- Independent tetrahedra Independent tetrahedra NesosilicatesNesosilicates
Examples: olivine garnetExamples: olivine garnet
[Si[Si22OO77]]6-6- Double tetrahedra Double tetrahedra SorosilicatesSorosilicates
Examples: lawsoniteExamples: lawsonite
n[SiOn[SiO33]]2-2- n = 3, 4, 6 n = 3, 4, 6 CyclosilicatesCyclosilicates
Examples: benitoite BaTi[SiExamples: benitoite BaTi[Si33OO99]]
axinite Caaxinite Ca33AlAl22BOBO33[Si[Si44OO1212]OH]OH
beryl Beberyl Be33AlAl22[Si[Si66OO1818]]
Mineral StructuresMineral StructuresSilicates are classified on the basis of Si-O polymerism Silicates are classified on the basis of Si-O polymerism
[SiO[SiO33]]2-2- single chains single chains Inosilicates Inosilicates [Si[Si44OO1111]]4-4- Double tetrahedra Double tetrahedra
pryoxenes pyroxenoidspryoxenes pyroxenoids amphiboles amphiboles
Mineral StructuresMineral StructuresSilicates are classified on the basis of Si-O polymerism Silicates are classified on the basis of Si-O polymerism
[Si[Si22OO55]]2-2- Sheets of tetrahedra Sheets of tetrahedra PhyllosilicatesPhyllosilicates
micas talc clay minerals serpentinemicas talc clay minerals serpentine
Mineral StructuresMineral StructuresSilicates are classified on the basis of Si-O polymerism Silicates are classified on the basis of Si-O polymerism
[SiO[SiO22] 3-D frameworks of tetrahedra: fully polymerized ] 3-D frameworks of tetrahedra: fully polymerized TectosilicatesTectosilicates
quartz and the silica minerals feldspars feldspathoids zeolitesquartz and the silica minerals feldspars feldspathoids zeolites
low-quartzlow-quartz
Mineral StructuresMineral StructuresNesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra
Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra
Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2
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projectionprojection
Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2
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perspectiveperspective
Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra 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
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Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra
Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra
Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2
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M1 and M2 as polyhedraM1 and M2 as polyhedra
Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra
Olivine Occurrences:Olivine Occurrences: Principally in mafic and ultramafic igneous and meta-Principally in mafic and ultramafic igneous and meta-
igneous rocksigneous rocks Fayalite in meta-ironstones and in some alkalic Fayalite in meta-ironstones and in some alkalic
granitoidsgranitoids Forsterite in some siliceous dolomitic marblesForsterite in some siliceous dolomitic marbles
Monticellite CaMgSiOMonticellite CaMgSiO44 Ca Ca M2 (larger ion, larger site) M2 (larger ion, larger site)
High grade metamorphic siliceous carbonatesHigh grade metamorphic siliceous carbonates
Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra 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 metamorphicSome high-Al igneousSome high-Al igneousAlso in some mantle peridotitesAlso in some mantle peridotites
Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra 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
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aa33
Inosilicates: single chains- Inosilicates: single chains- pyroxenespyroxenes
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]]
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Where are the Si-O-Si-O chains??Where are the Si-O-Si-O chains??
Inosilicates: single chains- pyroxenes 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)
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Inosilicates: single chains- pyroxenes 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)
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Inosilicates: single chains- pyroxenes 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)
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Inosilicates: single chains- pyroxenes 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)
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Inosilicates: single chains- pyroxenes 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)
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Inosilicates: single chains- pyroxenes 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 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)
SiOSiO44 as polygons as polygons
(and larger area)(and larger area)IV slabIV slab
IV slabIV slab
IV slabIV slab
IV slabIV slab
VI slabVI slab
VI slabVI slab
VI slabVI slab
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Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes
M1 octahedronM1 octahedron
Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes
M1 octahedronM1 octahedron
Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes
M1 octahedronM1 octahedron
(+) type by convention(+) type by convention
(+)
Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes
M1 octahedronM1 octahedron
This is a (-) typeThis is a (-) type
(-)
Inosilicates: single chains- pyroxenes 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 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 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 Inosilicates: single chains- pyroxenes
(+)(+)(+)(+)
Tetrehedra and M1 Tetrehedra and M1 octahedra share octahedra share
tetrahedral apical tetrahedral apical oxygen atoms oxygen atoms
Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes
The tetrahedral chain The tetrahedral chain above the M1s is thus above the M1s is thus offset from that below offset from that below
The M2 slabs have a The M2 slabs have a similar effectsimilar effect
The result is a The result is a monoclinicmonoclinic unit cell, unit cell, hence hence clinopyroxenesclinopyroxenes
Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes
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(+) M1(+) M1
(+) M2(+) M2
(+) M2(+) M2
OrthopyroxenesOrthopyroxenes have have alternating (+) and (-) alternating (+) and (-)
I-beams I-beams
the offsets thus the offsets thus compensate and result compensate and result in an in an orthorhombicorthorhombic
unit cellunit cell
This also explains the This also explains the double double aa cell dimension cell dimension and why orthopyroxenes and why orthopyroxenes
have have {210}{210} cleavages cleavages instead of {110) as in instead of {110) as in
clinopyroxenes (although clinopyroxenes (although both are at 90both are at 90oo))
Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes
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(+) M1(+) M1
(-) M1(-) M1
(-) M2(-) M2
(+) M2(+) M2
Pyroxene ChemistryPyroxene Chemistry
The general pyroxene formula: The general pyroxene formula:
WW1-P1-P (X,Y) (X,Y)1+P1+P Z Z22OO66
WhereWhere W = W = CaCa Na Na X = X = Mg FeMg Fe2+2+ Mn Ni Li Mn Ni Li Y = Al FeY = Al Fe3+3+ Cr Ti Cr Ti Z = Z = SiSi Al Al
Anhydrous Anhydrous so high-temperature or dry conditions so high-temperature or dry conditions favor pyroxenes over amphibolesfavor pyroxenes over amphiboles
Pyroxene ChemistryPyroxene Chemistry
The pyroxene quadrilateral and opx-cpx solvusThe pyroxene quadrilateral and opx-cpx solvusCoexisting opx + cpx in many rocks (pigeonite only in volcanics)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 ChemistryPyroxene Chemistry
““Non-quad” pyroxenesNon-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
PyroxenoidsPyroxenoids““Ideal” pyroxene chains with Ideal” pyroxene chains with
5.2 A repeat (2 tetrahedra) 5.2 A repeat (2 tetrahedra) become distorted as other become distorted as other cations occupy VI sitescations occupy VI sites
WollastoniteWollastonite (Ca (Ca M1) M1) 3-tet repeat3-tet repeat
RhodoniteRhodoniteMnSiOMnSiO33
5-tet repeat5-tet repeat
PyroxmangitePyroxmangite (Mn, Fe)SiO(Mn, Fe)SiO33
7-tet repeat7-tet repeat
PyroxenePyroxene2-tet repeat2-tet repeat
7.1 A12.5 A
17.4 A
5.2 A
Inosilicates: double chains- Inosilicates: double chains- amphibolesamphiboles
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
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Inosilicates: double chains- Inosilicates: double chains- amphibolesamphiboles
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
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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- Inosilicates: double chains- amphibolesamphiboles
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- Inosilicates: double chains- amphibolesamphiboles
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(+)(+) (+)(+)
(+)(+)
(+)(+)
(+)(+)
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: double chains- Inosilicates: double chains- amphibolesamphiboles
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, Al) (Mg, Fe, Al)55
[(Si,Al)[(Si,Al)88OO2222] (OH)] (OH)22
M1-M3 are small sitesM1-M3 are small sites
M4 is larger (Ca)M4 is larger (Ca)
A-site is really bigA-site is really big
Variety of sites Variety of sites great chemical rangegreat chemical range
Inosilicates: double chains- Inosilicates: double chains- amphibolesamphiboles
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, Al) (Mg, Fe, Al)55
[(Si,Al)[(Si,Al)88OO2222] (OH)] (OH)22
(OH) is in center of (OH) is in center of tetrahedral ring where O tetrahedral ring where O is a part of M1 and M3 is a part of M1 and M3
octahedraoctahedra
(OH)(OH)
See handout for more informationSee handout for more information
General formula:General formula:
WW0-10-1 X X22 Y Y55 [Z [Z88OO2222] (OH, F, Cl)] (OH, F, Cl)22
W = Na KW = Na K
X = Ca Na Mg FeX = Ca Na Mg Fe2+2+ (Mn Li) (Mn Li)
Y = Mg FeY = Mg Fe2+2+ Mn Al Fe Mn Al Fe3+3+ Ti Ti
Z = Si AlZ = Si Al
Again, the great variety of sites and sizes Again, the great variety of sites and sizes a great chemical range, and a great chemical range, and hence a broad stability rangehence a broad stability range
The The hydroushydrous nature implies an upper temperature stability limit nature implies an upper temperature stability limit
Amphibole ChemistryAmphibole Chemistry
Ca-Mg-Fe Amphibole “quadrilateral” (good analogy with pyroxenes)Ca-Mg-Fe Amphibole “quadrilateral” (good analogy with pyroxenes)
Amphibole ChemistryAmphibole Chemistry
Al and Na tend to stabilize the orthorhombic form in low-Ca amphiboles, so anthophyllite 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 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 siteHornblende has Al in the tetrahedral site
Geologists traditionally use the term “hornblende” as a catch-all term for practically 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 any dark amphibole. Now the common use of the microprobe has petrologists casting “hornblende” into end-member compositions and naming amphiboles casting “hornblende” into end-member compositions and naming amphiboles after a well-represented end-member.after a well-represented end-member.
Sodic amphiboles Sodic amphiboles
Glaucophane: NaGlaucophane: Na2 2 MgMg3 3 AlAl2 2 [Si[Si88OO2222] (OH)] (OH)22
Riebeckite: NaRiebeckite: Na2 2 FeFe2+2+3 3 FeFe3+3+
2 2 [Si[Si88OO2222] (OH)] (OH)22
Sodic amphiboles are commonly blue, and often called “blue amphiboles”Sodic amphiboles are commonly blue, and often called “blue amphiboles”
Amphibole ChemistryAmphibole Chemistry
Tremolite (Ca-Mg) occurs in meta-carbonatesTremolite (Ca-Mg) occurs in meta-carbonates
Actinolite occurs in low-grade metamorphosed basic igneous rocksActinolite occurs in low-grade metamorphosed basic igneous rocks
Orthoamphiboles and cummingtonite-grunerite (all Ca-free, Mg-Fe-rich Orthoamphiboles and cummingtonite-grunerite (all Ca-free, Mg-Fe-rich amphiboles) are metamorphic and occur in meta-ultrabasic rocks and some amphiboles) are metamorphic and occur in meta-ultrabasic rocks and some meta-sediments. The Fe-rich grunerite occurs in meta-ironstonesmeta-sediments. The Fe-rich grunerite occurs in meta-ironstones
The complex solid solution called hornblende occurs in a broad variety of both The complex solid solution called hornblende occurs in a broad variety of both igenous and metamorphic rocksigenous and metamorphic rocks
Sodic amphiboles are predominantly metamorphic where they are Sodic amphiboles are predominantly metamorphic where they are characteristic of high P/T subduction-zone metamorphism (commonly called characteristic of high P/T subduction-zone metamorphism (commonly called “blueschist” in reference to the predominant blue sodic amphiboles “blueschist” in reference to the predominant blue sodic amphiboles
Riebeckite occurs commonly in sodic granitoid rocksRiebeckite occurs commonly in sodic granitoid rocks
Amphibole OccurrencesAmphibole Occurrences
InosilicatesInosilicates
Pyroxenes and amphiboles are very similar:Pyroxenes and amphiboles are very similar: Both have chains of SiOBoth have chains of SiO44 tetrahedra tetrahedra The chains are connected into stylized I-beams by M octahedraThe chains are connected into stylized I-beams by M octahedra High-Ca monoclinic forms have all the T-O-T offsets in the same directionHigh-Ca monoclinic forms have all the T-O-T offsets in the same direction Low-Ca orthorhombic forms have alternating (+) and (-) offsetsLow-Ca orthorhombic forms have alternating (+) and (-) offsets
++++ ++
++
++++++
++++ ---- --
----
--
++
++++
aa
aa
++++ ++
++++ ++
++++ ++
++++ ++
----
--
----
--
ClinopyroxeneClinopyroxene
OrthopyroxeneOrthopyroxene OrthoamphiboleOrthoamphibole
ClinoamphiboleClinoamphibole
InosilicatesInosilicates
Cleavage angles can be interpreted in terms of weak bonds in M2 sites Cleavage angles can be interpreted in terms of weak bonds in M2 sites (around I-beams instead of through them)(around I-beams instead of through them)
Narrow single-chain I-beams Narrow single-chain I-beams 90 90oo cleavages in pyroxenes while wider double- cleavages in pyroxenes while wider double-chain I-beams chain I-beams 60-120 60-120oo cleavages in amphiboles cleavages in amphiboles
pyroxenepyroxene amphiboleamphibole
aa
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SiOSiO44 tetrahedra polymerized into 2-D sheets: [Si tetrahedra polymerized into 2-D sheets: [Si22OO55]]
Apical O’s are unpolymerized and are bonded to other constituentsApical O’s are unpolymerized and are bonded to other constituents
PhyllosilicatesPhyllosilicates
Tetrahedral layers are bonded to octahedral layers Tetrahedral layers are bonded to octahedral layers
(OH) pairs are located in center of T rings where no apical O(OH) pairs are located in center of T rings where no apical O
PhyllosilicatesPhyllosilicates
Octahedral layers can be understood by analogy with hydroxidesOctahedral layers can be understood by analogy with hydroxides
PhyllosilicatesPhyllosilicates
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
PhyllosilicatesPhyllosilicates
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
PhyllosilicatesPhyllosilicates
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
PhyllosilicatesPhyllosilicates
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
SerpentineSerpentine
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
SerpentineSerpentine
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.
PhyllosilicatesPhyllosilicates
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)
PhyllosilicatesPhyllosilicates
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)
PhyllosilicatesPhyllosilicates
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
PhyllosilicatesPhyllosilicates
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 A Summary of
Phyllosilicate StructuresPhyllosilicate Structures
PhyllosilicatesPhyllosilicates
Fig 13.84 Klein and Hurlbut Manual of Mineralogy, © John Wiley & Sons
Chlorite: (Mg, Fe)Chlorite: (Mg, Fe)33 [(Si, Al) [(Si, Al)44OO1010] (OH)] (OH)22 (Mg, Fe) (Mg, Fe)33 (OH) (OH)66
= T - O - T - (brucite) - T - O - T - (brucite) - T - O - T -= T - O - T - (brucite) - T - O - T - (brucite) - T - O - T -
Very hydrated (OH)Very hydrated (OH)88, so low-temperature stability (low-T metamorphism , so low-temperature stability (low-T metamorphism
and alteration of mafics as cool)and alteration of mafics as cool)
PhyllosilicatesPhyllosilicates
Why are there single-chain-, double-chain-, and sheet-polymer types, Why are there single-chain-, double-chain-, and sheet-polymer types, and not triple chains, quadruple chains, etc??and not triple chains, quadruple chains, etc??
““Biopyriboles”Biopyriboles”
It turns out that there are some It turns out that there are some intermediate types, predicted by intermediate types, predicted by J.B. Thompson and discovered in J.B. Thompson and discovered in 1977 Veblen, Buseck, and 1977 Veblen, Buseck, and BurnhamBurnham
Cover of Science: anthophyllite Cover of Science: anthophyllite (yellow) reacted to form chesterite (yellow) reacted to form chesterite (blue & green) and jimthompsonite (blue & green) and jimthompsonite (red)(red)
Streaked areas are highly Streaked areas are highly disordereddisordered
““Biopyriboles”Biopyriboles”
Cover of Science, October 28, 1977 © AAAS
HRTEM image of anthophyllite (left) with typical double-chain widthHRTEM image of anthophyllite (left) with typical double-chain width
Jimthompsonite (center) has triple-chainsJimthompsonite (center) has triple-chains
Chesterite is an ordered alternation of double- and triple-chainsChesterite 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 widthDisordered structures show 4-chain widths and even a 7-chain width
Obscures the distinction between pyroxenes, amphiboles, and micas Obscures the distinction between pyroxenes, amphiboles, and micas (hence the term biopyriboles: (hence the term biopyriboles: biobiotite-tite-pyrpyroxene-amphoxene-amphiboleibole))
““Biopyriboles”Biopyriboles”Fig. 7, Veblen et al (1977) Science 198 © AAAS
TectosilicatesTectosilicates
Stishovite
Coesite
- quartz
- quartz
Liquid
TridymiteCristobalite
600 1000 1400 1800 2200 2600
2
4
6
8
10P
ress
ure
(GP
a)
Temperature oC
After Swamy and Saxena (1994) J. Geophys. Res., 99, 11,787-11,794.
TectosilicatesTectosilicates
Low QuartzLow Quartz
001 Projection Crystal Class 32001 Projection Crystal Class 32
Stishovite
Coesite
- quartz
- quartz
Liquid
TridymiteCristobalite
TectosilicatesTectosilicates
High Quartz at 581High Quartz at 581ooCC
001 Projection Crystal Class 622001 Projection Crystal Class 622
Stishovite
Coesite
- quartz
- quartz
Liquid
TridymiteCristobalite
TectosilicatesTectosilicates
CristobaliteCristobalite
001 Projection Cubic Structure001 Projection Cubic Structure
Stishovite
Coesite
- quartz
- quartz
Liquid
TridymiteCristobalite
TectosilicatesTectosilicates
StishoviteStishovite
High pressure High pressure Si SiVIVI
Stishovite
Coesite
- quartz
- quartz
Liquid
TridymiteCristobalite
TectosilicatesTectosilicates
Low Quartz StishoviteLow Quartz Stishovite
SiSiIVIV Si SiVIVI
TectosilicatesTectosilicates
FeldsparsFeldspars
Albite: Albite: NaNaAlAlSiSi33OO88
Substitute two Substitute two AlAl3+3+ for Si for Si4+4+ allows Caallows Ca2+2+ to to be addedbe added
Substitute AlSubstitute Al3+3+ for Sifor Si4+4+ allows allows NaNa++ or K or K++ to be to be addedadded