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DESCRIPTION
Back to silicate structures:. nesosilicates. phyllosilicates. sorosilicates. inosilicates. cyclosilictaes. tectosilicates. b. c. Nesosilicates: independent SiO 4 tetrahedra. projection. Olivine (100) view blue = M1 yellow = M2. (+). T M1 T - PowerPoint PPT PresentationTRANSCRIPT
Back to silicate structures:Back to silicate structures:
nesosilicatesnesosilicates
inosilicatesinosilicates
tectosilicatestectosilicates
phyllosilicatesphyllosilicates
cyclosilictaescyclosilictaes
sorosilicatessorosilicates
Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra
Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2
bb
cc
projectionprojection
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
(+)(+)(+)(+)
The pyroxene The pyroxene structure is then structure is then
composed of composed of alternation I-beamsalternation I-beams
Orthoopyroxenes Orthoopyroxenes have I-beams oriented have I-beams oriented in alternate direction in alternate direction
in different layersin different layers
(-)(-)
(+)(+)(+)(+)
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
cc
aa
(+) 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
Inosilicates: single chains- pyroxenes Inosilicates: single chains- pyroxenes
cc
aa
(+) 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)
DiopsideDiopsideCaMgSiCaMgSi22OO66
HedenbergiteHedenbergite CaFeSiCaFeSi22OO66
Wollastonite CaWollastonite Ca22SiSi22OO66
EnstatiteEnstatiteMgMg22SiSi22OO66
FerrosiliteFerrosiliteFeFe22SiSi22OO66
orthopyroxenes
clinopyroxenes
pigeonite
•OrthopyroxenesOrthopyroxenes – solid soln – solid soln between Enstatite-Ferrosilitebetween Enstatite-Ferrosilite•Clinopyroxenes – solid soln – solid soln between Diopside-Hedenbergitebetween Diopside-Hedenbergite
Joins – lines between end Joins – lines between end members – limited mixing members – limited mixing away from joinaway from join
Orthopyroxene - ClinopyroxeneOrthopyroxene - ClinopyroxeneOPX and CPX have different crystal structures OPX and CPX have different crystal structures
– results in a complex solvus between them– results in a complex solvus between themCoexisting opx + cpx in many rocks (pigeonite only in volcanics)Coexisting opx + cpx in many rocks (pigeonite only in volcanics)
DiopsideDiopsideCaMgSiCaMgSi22OO66
HedenbergiteHedenbergite CaFeSiCaFeSi22OO66
Wollastonite CaWollastonite Ca22SiSi22OO66
EnstatiteEnstatiteMgMg22SiSi22OO66
FerrosiliteFerrosiliteFeFe22SiSi22OO66
orthopyroxenes
clinopyroxenes
pigeonite
(Mg,Fe)(Mg,Fe)22SiSi22OO66 Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO66
pigeonite clinopyroxenes
orthopyroxenes
SolvusSolvus
12001200ooCC
10001000ooCC
800800ooCC
OPXOPX CPXCPX
CPXCPX
OPXOPX
Orthopyroxene – ClinopyroxeneOrthopyroxene – Clinopyroxenesolvus T dependencesolvus T dependence
Complex solvus – the ‘stability’ of a particular mineral changes Complex solvus – the ‘stability’ of a particular mineral changes with T. A different mineral’s ‘stability’ may change with T with T. A different mineral’s ‘stability’ may change with T differently…differently…
OPX-CPX exsolution lamellae OPX-CPX exsolution lamellae Geothermometer… Geothermometer…
MiscibilityGap
FsFsEnEn
DiDi HdHd
FsFsEnEn
DiDi HdHd
OPXOPXOPXOPX
CPXCPX CPXCPX
pigeonite
augite
orthopyroxene
Pigeonite + orthopyroxene
orthopyroxene
Subcalcic augite
pigeonite
augite
MiscibilityGap
800800ºCºC 12001200ºCºC
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
Back to silicate structures:Back to silicate structures:
nesosilicatesnesosilicates
inosilicatesinosilicates
tectosilicatestectosilicates
phyllosilicatesphyllosilicates
cyclosilictaescyclosilictaes
sorosilicatessorosilicates
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
bb
a si
na
sin
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
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- 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
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: 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 igneous and metamorphic rocksigneous 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
bb
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
Igneous MineralsIgneous Minerals
Quartz, Feldspars (plagioclase and alkaline), Quartz, Feldspars (plagioclase and alkaline), Olivines, Pyroxenes, AmphibolesOlivines, Pyroxenes, Amphiboles
Accessory Minerals – mostly in small quantities Accessory Minerals – mostly in small quantities or in ‘special’ rocksor in ‘special’ rocks Magnetite (FeMagnetite (Fe33OO44))
Ilmenite (FeTiOIlmenite (FeTiO33))
Apatite (CaApatite (Ca55(PO(PO44))33(OH,F,Cl)(OH,F,Cl)
Zircon (ZrSiOZircon (ZrSiO44))
Titanite (CaTiSiOTitanite (CaTiSiO55))
Pyrite (FeSPyrite (FeS22))
Fluorite (CaFFluorite (CaF22))