Feldspar Group
description
Transcript of Feldspar Group
Feldspar GroupFeldspar Group
Most abundant mineral in Most abundant mineral in the crust the crust 6 of 7 most 6 of 7 most common elementscommon elements
Defined through 3 end-Defined through 3 end-members members Albite (Na), Anorthite (Ca), Albite (Na), Anorthite (Ca),
Orthoclase (K)Orthoclase (K) Comprised of 2 series:Comprised of 2 series:
Albite-anorthite (Na-Ca)Albite-anorthite (Na-Ca) Albite-orthoclase (Na-K)Albite-orthoclase (Na-K)
TectosilicatesTectosilicatesFeldsparsFeldspars
Albite: Albite: NaNaAlAlSiSi33OO88
Substitute two Substitute two AlAl3+3+ for Si for Si4+4+ allows Caallows Ca2+2+ to be to be addedaddedAlbite-AnorthiteAlbite-Anorthite
Substitute AlSubstitute Al3+3+ for Sifor Si4+4+ allows allows NaNa++ or K or K++ to be to be addedaddedAlbite-OrthoclaseAlbite-Orthoclase
Feldspar Group – Albite-Anorthite seriesFeldspar Group – Albite-Anorthite series Complete solid solution Complete solid solution Plagioclase FeldsparsPlagioclase Feldspars 6 minerals6 minerals
Albite (Na)Albite (Na) OligoclaseOligoclase AndesineAndesine LabradoriteLabradorite BytowniteBytownite Anorthite (Ca)Anorthite (Ca)
Albite-Anorthite double dutyAlbite-Anorthite double duty End-members (Pure Na or Ca)End-members (Pure Na or Ca) Minerals 90-99.99% Na or CaMinerals 90-99.99% Na or Ca
Notation:Notation: AnAnxxAbAbyy An An2020AbAb8080=Oligoclase=Oligoclase
Feldspar Group – Albite-Anorthite seriesFeldspar Group – Albite-Anorthite series Optical techniques to Optical techniques to
distinguish between distinguish between plagioclase feldspars:plagioclase feldspars: Michel-Levy Method – uses Michel-Levy Method – uses
extinction angles of extinction angles of twinned forms to determine twinned forms to determine An-Ab contentAn-Ab content
Combined Carlsbad-Albite Combined Carlsbad-Albite Method Method uses Michel- uses Michel-Levy technique for both Levy technique for both sides of a twin formsides of a twin form
Staining techniqueStaining technique
Stains that attach Stains that attach to K really well to K really well (Like Co(NO3)2 ) (Like Co(NO3)2 ) will higlight the K-will higlight the K-feldspars quickly feldspars quickly and easily in hand and easily in hand specimen or thin specimen or thin sectionsection
Feldspar Group – Albite-Orthoclase seriesFeldspar Group – Albite-Orthoclase series
High – T mineralsHigh – T minerals SanidineSanidine AnorthoclaseAnorthoclase MonalbiteMonalbite High AlbiteHigh Albite
Low Temperature Low Temperature exsolution at solvusexsolution at solvus Chicken soup Chicken soup
separationseparation Forms 2 minerals, in igneous Forms 2 minerals, in igneous
rocks these are typically rocks these are typically intergrowths, or exsolution intergrowths, or exsolution lamellae – perthitic texturelamellae – perthitic texture
Miscibility Gap
microcline
orthoclase
sanidine
anorthoclasemonalbite
high albite
low albite
intermediate albite
OrthoclaseKAlSi3O8
AlbiteNaAlSi3O8
% NaAlSi3O8
Tem
pera
ture
(T
empe
ratu
re ( º
C)
ºC)
300300
900900
700700
500500
11001100
1010 9090707050503030
Several minerals – Several minerals – Alkali FeldsparsAlkali Feldspars
Alkali Feldspar ExsolutionAlkali Feldspar Exsolution
Melt cools past solvus Melt cools past solvus (line defining (line defining miscibility gap)miscibility gap)
Anorthoclase, that had Anorthoclase, that had formed (through formed (through liquidus/solidus) liquidus/solidus) separates (if cooling is separates (if cooling is slow enough) to form slow enough) to form orthoclase orthoclase andand low low albitealbite
In hand sample – In hand sample – schiller effect schiller effect play play of colors caused by of colors caused by lamellaelamellae
Miscibility Gap
microcline
orthoclase
sanidine
anorthoclase
monalbite
high albite
low albite
intermediate albite
OrthoclaseKAlSi3O8
AlbiteNaAlSi3O8
% NaAlSi3O8
Tem
pera
ture
(T
empe
ratu
re ( º
C)
ºC)
300300
900900
700700
500500
11001100
1010 9090707050503030
Liquid
Alkali Feldspar lamellaeAlkali Feldspar lamellae
Feldspathoid GroupFeldspathoid Group Very similar to Very similar to
feldspars and zeolitesfeldspars and zeolites Include Nepheline, Include Nepheline,
Analcime, and LeuciteAnalcime, and Leucite Also framework Also framework
silicates, but with silicates, but with another Al substitution another Al substitution for Sifor Si
Only occur in Only occur in undersaturated rocks undersaturated rocks (no free Quartz, Si-(no free Quartz, Si-poor) because they poor) because they react with SiOreact with SiO22 to form to form
feldsparsfeldspars
Feldspathoids, Cont.Feldspathoids, Cont.
NephelineNepheline Important Important
feldspathoid feldspathoid mineralmineral
Indicates Indicates undersaturated undersaturated magmamagma
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
Olivine – complete solid solution Olivine – complete solid solution Forsterite-Fayalite Forsterite-Fayalite Fo FoxxFaFayy
Fayalite – Fe end-member Fayalite – Fe end-member
Forsterite – Mg end-memberForsterite – Mg end-member
Olivine Occurrences:Olivine Occurrences: Principally in mafic and ultramafic igneous and meta-igneous Principally in mafic and ultramafic igneous and meta-igneous
rocksrocks Fayalite in meta-ironstones and in some alkalic granitoidsFayalite in meta-ironstones and in some alkalic granitoids 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
Distinguishing Forsterite-FayaliteDistinguishing Forsterite-Fayalite
Petrographic MicroscopePetrographic Microscope Index of refraction Index of refraction careful of zoning!! careful of zoning!! 2V different in different composition ranges2V different in different composition ranges Pleochroism/ color slightly differentPleochroism/ color slightly different
Spectroscopic techniques – many ways to Spectroscopic techniques – many ways to determine Fe vs. Mgdetermine Fe vs. Mg
Same space group (Pbnm), Orthorhombic, slight Same space group (Pbnm), Orthorhombic, slight differences in unit cell dimensions onlydifferences in unit cell dimensions only
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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na
sin
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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a si
na
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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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na
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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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na
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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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na
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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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a si
na
sin
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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na
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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
Orthopyroxenes have Orthopyroxenes have alternating (+) and (-) alternating (+) and (-)
orientationsorientations
(+)(+)
(+)(+)(+)(+)
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
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
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
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))
Sphene (a.k.a. Titanite) (CaTiSiOSphene (a.k.a. Titanite) (CaTiSiO55))
Pyrite (FeSPyrite (FeS22))
Fluorite (CaFFluorite (CaF22))