8 structures

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


[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]]


[SiO[SiO33]]2-2- single chains single chains Inosilicates Inosilicates [Si[Si44OO1111]]4-4- Double tetrahedra Double tetrahedra

pryoxenes pyroxenoidspryoxenes pyroxenoids amphiboles amphiboles


[Si[Si22OO55]]2-2- Sheets of tetrahedra Sheets of tetrahedra PhyllosilicatesPhyllosilicates

micas talc clay minerals serpentinemicas talc clay minerals serpentine


[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

bb

cc

projectionprojection


bb

cc

perspectiveperspective



M1 in rows M1 in rows and share and share edgesedges

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

Some M2 and Some M2 and M1 share M1 share edgesedges

bb

aa




bb

cc

M1 and M2 as polyhedraM1 and M2 as polyhedra


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


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


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

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]]

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 Inosilicates: single chains- pyroxenes


bb

a si

na

sin



Perspective viewPerspective view



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

bb

a si

na

sin


M1 octahedronM1 octahedron



(+) type by convention(+) type by convention

(+)



This is a (-) typeThis is a (-) type

(-)


TT

M1M1

TT

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

structure.structure.


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

(+)(+)

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

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


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

(+)(+)

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


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

Tetrehedra and M1 Tetrehedra and M1 octahedra share octahedra share

tetrahedral apical tetrahedral apical oxygen atoms oxygen atoms


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


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

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))


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


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


““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

bb

a si

na

sin


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


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)


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

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





[(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





[(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)


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”


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

bb

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


Octahedral layers can be understood by analogy with hydroxidesOctahedral layers can be understood by analogy with hydroxides


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


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


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


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

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

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


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

vdwvdw

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.


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



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



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


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


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)


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.


Low QuartzLow Quartz

001 Projection Crystal Class 32001 Projection Crystal Class 32

Stishovite

Coesite

- quartz

- quartz

Liquid



High Quartz at 581High Quartz at 581ooCC

001 Projection Crystal Class 622001 Projection Crystal Class 622

Stishovite

Coesite

- quartz

- quartz

Liquid



CristobaliteCristobalite

001 Projection Cubic Structure001 Projection Cubic Structure

Stishovite

Coesite

- quartz

- quartz

Liquid



StishoviteStishovite

High pressure High pressure Si SiVIVI

Stishovite

Coesite

- quartz

- quartz

Liquid



Low Quartz StishoviteLow Quartz Stishovite

SiSiIVIV Si SiVIVI


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

8 structures

Documents

quartz liquidcristobalite

independent

independent

independent

ca uvarovite

m2 sites

m1 octahedron

al pyrope