structures and chemistry of silicategsi.ir/images//structures and chemistry of...

Structures and Chemistry of silicateStructures and Chemistry of silicate

by:by:

SeyedSeyed mohsenmohsen hoseinihoseini zadezade


Silicates are classified on the basis of SiSilicates are classified on the basis of Si--O polymerism O polymerism

The culprit: the [SiOThe culprit: the [SiO44]]44-- tetrahedrontetrahedron



[SiO[SiO44]]44-- Independent tetrahedra Independent tetrahedra NesosilicatesNesosilicates

Examples: olivine garnetExamples: olivine garnet

[Si[Si22OO77]]66-- Double tetrahedra Double tetrahedra SorosilicatesSorosilicates

Examples: lawsoniteExamples: lawsonite

n[SiOn[SiO33]]22-- 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]]22-- single chains single chains Inosilicates Inosilicates [Si[Si44OO1111]]

44-- Double tetrahedraDouble tetrahedra

pryoxenes pyroxenoidspryoxenes pyroxenoids amphibolesamphiboles



[Si[Si22OO55]]22-- Sheets of tetrahedra Sheets of tetrahedra PhyllosilicatesPhyllosilicates

micas talc clay minerals serpentinemicas talc clay minerals serpentine



[SiO[SiO22] 3] 3--D frameworks of tetrahedra: fully polymerized D frameworks of tetrahedra: fully polymerized TectosilicatesTectosilicates

quartz and the silica minerals feldspars feldspathoids zeolitesquartz and the silica minerals feldspars feldspathoids zeolites

lowlow--quartzquartz


Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra


Olivine (Olivine (100100) view blue = M) view blue = M1 1 yellow = Myellow = M22

bb

cc

projectionprojection

Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2

bb

cc

perspectiveperspective


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 alayers in a--c c

that share that share

corners corners

Some M2 Some M2

and M1 share and M1 share

edgesedges

bb

aa



Olivine (Olivine (100100) view blue = M) view blue = M1 1 yellow = Myellow = M22

bb

cc

M1 and M2 as polyhedraM1 and M2 as polyhedra

Nesosilicates: independent SiONesosilicates: independent SiO44 tetrahedratetrahedra

Olivine Occurrences:Olivine Occurrences:

Principally in mafic and ultramafic igneous and metaPrincipally in mafic and ultramafic igneous and meta--

igneous rocksigneous rocks

Fayalite in metaFayalite in meta--ironstones and in some alkalic 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: A22++33 BB33++

22 [SiO[SiO44]]3 3

“Pyralspites”“Pyralspites” -- B = AlB = Al

PyPyrope: Mgrope: Mg33 AlAl22 [SiO[SiO44]]3 3

AlAlmandine: Femandine: Fe33 AlAl22 [SiO[SiO44]]33

SpSpessartine: Mnessartine: Mn33 AlAl22 [SiO[SiO44]]33

“Ugrandites”“Ugrandites” -- A = CaA = Ca

UUvarovite: Cavarovite: Ca33 CrCr22 [SiO[SiO44]]33

GrGrossularite: Caossularite: Ca33 AlAl22 [SiO[SiO44]]33

AndAndradite: Caradite: Ca33 FeFe22 [SiO[SiO44]]33

Occurrence:Occurrence:

Mostly metamorphicMostly metamorphic

Some highSome high--Al igneousAl igneous

Also 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 BB3+3+

22 [SiO[SiO44]]3 3

“Pyralspites”“Pyralspites” -- B = AlB = Al

PyPyrope: Mgrope: Mg33 AlAl22 [SiO[SiO44]]3 3

AlAlmandine: Femandine: Fe33 AlAl22 [SiO[SiO44]]33

SpSpessartine: Mnessartine: Mn33 AlAl22 [SiO[SiO44]]33

“Ugrandites”“Ugrandites” -- A = CaA = Ca

UUvarovite: Cavarovite: Ca33 CrCr22 [SiO[SiO44]]33

GrGrossularite: Caossularite: Ca33 AlAl22 [SiO[SiO44]]33

AndAndradite: Caradite: Ca33 FeFe22 [SiO[SiO44]]33

Occurrence:Occurrence:

Mostly metamorphicMostly metamorphicPyralspites in metaPyralspites in meta--shalesshales

Ugrandites in metaUgrandites in meta--carbonatescarbonates

Some highSome high--Al igneousAl igneous

Also in some mantle peridotitesAlso in some mantle peridotites

aa11

aa22

aa33

Inosilicates: single chainsInosilicates: 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 s

ina

sin

Where are the SiWhere are the Si--OO--SiSi--O chains??O chains??

Inosilicates: single chainsInosilicates: single chains-- pyroxenes pyroxenes


bb

a s

ina

sin


Diopside (Diopside (001001) view blue = Si purple = M) view blue = Si purple = M1 1 (Mg) yellow = M(Mg) yellow = M2 2 (Ca)(Ca)

bb

a s

ina

sin



bb

a s

ina

sin



Perspective viewPerspective view



SiOSiO44 as polygonsas 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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a s

ina

sin


M1 octahedronM1 octahedron


M1 octahedronM1 octahedron

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

(+)


MM1 1 octahedronoctahedron

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

(-)


TT

M1M1

TT

Creates an “ICreates an “I--beam” beam”

like unit in the like unit in the

structure.structure.


TT

M1M1

TT

Creates an “ICreates an “I--beam” 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 Ialternating I--beamsbeams

Clinopyroxenes have Clinopyroxenes have

all Iall I--beams oriented 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 Ialternation I--beamsbeams

Clinopyroxenes have Clinopyroxenes have

all Iall I--beams oriented beams oriented

the same: all are (+) the same: all are (+)

in this orientation in this orientation

(+)(+)

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


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

Tetrehedra and MTetrehedra and M1 1

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

(+) M(+) M11

(+) M(+) M22

(+) M2(+) M2

OrthopyroxenesOrthopyroxenes have have

alternating (+) and (alternating (+) and (--) )

II--beams 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 dimensioncell 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

((--) M) M22

(+) M(+) M22

Pyroxene ChemistryPyroxene Chemistry

The general pyroxene formula: The general pyroxene formula:

WW11--PP (X,Y)(X,Y)1+P1+P ZZ22OO66

WhereWhere

W = W = CaCa NaNa

X = X = Mg FeMg Fe2+2+ Mn Ni LiMn Ni Li

Y = Al FeY = Al Fe3+3+ Cr TiCr Ti

Z = Z = SiSi AlAl

Anhydrous Anhydrous so highso high--temperature or dry conditions temperature or dry conditions

favor pyroxenes over amphibolesfavor pyroxenes over amphiboles


The pyroxene quadrilateral and opxThe pyroxene quadrilateral and opx--cpx solvuscpx solvusCoexisting opx + cpx in many rocks (pigeonite only in volcanics)Coexisting opx + cpx in many rocks (pigeonite only in volcanics)

DiopsideDiopside HedenbergiteHedenbergite

WollastoniteWollastonite

EnstatiteEnstatite FerrosiliteFerrosilite

orthopyroxenes

clinopyroxenes

pigeonite (Mg,Fe)(Mg,Fe)22SiSi22OO66 Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO66

pigeonite

orthopyroxenes

SolvusSolvus

12001200ooCC

10001000ooCC

800800ooCC


“Non“Non--quad” pyroxenesquad” pyroxenesJadeiteJadeite

NaAlSiNaAlSi22OO66

Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO66

AegirineAegirine

NaFeNaFe3+3+SiSi22OO66

DiopsideDiopside--HedenbergiteHedenbergite

CaCa--Tschermack’s 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

55..2 2 A repeat (A repeat (2 2 tetrahedra) tetrahedra)

become distorted as other become distorted as other

cations occupy VI sitescations occupy VI sites

WollastoniteWollastonite

(Ca (Ca MM11) )

33--tet repeattet repeat

RhodoniteRhodonite

MnSiOMnSiO33


PyroxmangitePyroxmangite

(Mn, Fe)SiO(Mn, Fe)SiO33


PyroxenePyroxene


7.1 A12.5 A

17.4 A

5.2 A

Inosilicates: double chainsInosilicates: double chains-- amphibolesamphiboles

Tremolite (Tremolite (001001) view blue = Si purple = M) view blue = Si purple = M1 1 rose = Mrose = M2 2 gray = Mgray = M3 3 (all Mg)(all Mg)

yellow = Myellow = M4 4 (Ca)(Ca)

Tremolite:Tremolite:

CaCa22MgMg55 [Si[Si88OO2222] (OH)] (OH)22

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a s

ina

sin


Hornblende:Hornblende:

(Ca, Na)(Ca, Na)22--3 3 (Mg, Fe, Al)(Mg, Fe, Al)55

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

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a s

ina

sin

Hornblende (Hornblende (001001) view dark blue = Si, Al purple = M) view dark blue = Si, Al purple = M1 1 rose = Mrose = M2 2

light blue = Mlight blue = M3 3 (all Mg, Fe) yellow ball = M(all Mg, Fe) yellow ball = M4 4 (Ca) purple ball = A (Na)(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)


(Ca, Na)(Ca, Na)22--3 3 (Mg, Fe, (Mg, Fe,

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

(OH)(OH)22

Same ISame I--beam beam

architecture, but architecture, but

the Ithe I--beams are beams are

fatter (double fatter (double

chains)chains)


bb

a s

ina

sin

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

(+)(+)

(+)(+)

(+)(+)

Same ISame I--beam beam

architecture, but architecture, but

the Ithe I--beams are beams are

fatter (double fatter (double

chains)chains)

All are (+) on All are (+) on

clinoamphiboles clinoamphiboles

and alternate in and alternate in

orthoamphibolesorthoamphiboles


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)



(Ca, Na)(Ca, Na)22--3 3 (Mg, Fe, (Mg, Fe,

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

(OH)(OH)22







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

M1M1--M3 are small sitesM3 are small sites

M4 is larger (Ca)M4 is larger (Ca)

AA--site is really bigsite 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:

WW00--11 XX22 YY55 [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 FeMn Al Fe3+3+ TiTi

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 limitnature implies an upper temperature stability limit

Amphibole ChemistryAmphibole Chemistry

CaCa--MgMg--Fe Amphibole “quadrilateral” (good analogy with pyroxenes)Fe Amphibole “quadrilateral” (good analogy with pyroxenes)

Amphibole ChemistryAmphibole Chemistry

Al and Na tend to stabilize the orthorhombic form in lowAl and Na tend to stabilize the orthorhombic form in low--Ca amphiboles, so anthophyllite Ca amphiboles, so anthophyllite

gedrite orthorhombic series extends to Fegedrite orthorhombic series extends to Fe--rich gedrite in more Narich gedrite in more Na--AlAl--rich compositionsrich compositions

TremoliteTremolite

CaCa22MgMg55SiSi88OO2222(OH)(OH)22

FerroactinoliteFerroactinolite

CaCa22FeFe55SiSi88OO2222(OH)(OH)22

AnthophylliteAnthophyllite

MgMg77SiSi88OO2222(OH)(OH)22FeFe77SiSi88OO2222(OH)(OH)22

Actinolite

Cummingtonite-grunerite

OrthoamphibolesOrthoamphiboles

ClinoamphibolesClinoamphiboles

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 IThe chains are connected into stylized I--beams by M octahedrabeams by M octahedra

HighHigh--Ca monoclinic forms have all the TCa monoclinic forms have all the T--OO--T offsets in the same directionT offsets in the same direction

LowLow--Ca orthorhombic forms have alternating (+) and (Ca orthorhombic forms have alternating (+) and (--) offsets) 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(around I--beams instead of through them)beams instead of through them)

Narrow singleNarrow single--chain Ichain I--beams beams 9090oo cleavages in pyroxenes while wider doublecleavages in pyroxenes while wider double--

chain Ichain I--beams beams 6060--120120oo cleavages in amphiboles cleavages in amphiboles

pyroxenepyroxene amphiboleamphibole

aa

bb

SiOSiO44 tetrahedra polymerized into 2tetrahedra polymerized into 2--D sheets: [SiD 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 chargefor charge--balance reasonsbalance reasons

BruciteBrucite--type layers may be called type layers may be called trioctahedraltrioctahedral and gibbsiteand gibbsite--type type dioctahedraldioctahedral

aa11

aa22


Kaolinite:Kaolinite: AlAl22 [Si[Si22OO55] (OH)] (OH)44

TT--layers and layers and didiocathedral (Alocathedral (Al3+3+) layers ) layers

(OH) at center of T(OH) at center of T--rings and fill base of VI layer 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 Tweak van der Waals bonds between T--O groups O groups


Serpentine:Serpentine: MgMg33 [Si[Si22OO55] (OH)] (OH)44

TT--layers and layers and tritriocathedral (Mgocathedral (Mg22++) layers ) layers

(OH) at center of T(OH) at center of T--rings and fill base of VI layer 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 Tweak van der Waals bonds between T--O groups O groups

SerpentineSerpentine

Octahedra are a bit larger than tetrahedral Octahedra are a bit larger than tetrahedral

match, so they cause bending of the Tmatch, so they cause bending of the T--O O

layers (after Klein and Hurlbut, 1999).layers (after Klein and Hurlbut, 1999).

Antigorite maintains a Antigorite maintains a

sheetsheet--like form by 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: AlAl22 [Si[Si44OO1010] (OH)] (OH)22

TT--layer layer -- didiocathedral (Alocathedral (Al3+3+) layer ) layer -- TT--layer 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 weak van der Waals bonds between T -- O O -- T groups T groups



Talc:Talc: MgMg33 [Si[Si44OO1010] (OH)] (OH)22

TT--layer layer -- tritriocathedral (Mgocathedral (Mg2+2+) layer ) layer -- TT--layer 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 weak van der Waals bonds between T -- O O -- T groups T groups



Muscovite:Muscovite: KK AlAl22 [Si[Si33AlAlOO1010] (OH)] (OH)2 2 (coupled K (coupled K -- AlAlIVIV))

TT--layer layer -- didiocathedral (Alocathedral (Al33++) layer ) layer -- TT--layer layer -- KK

T T

O O

T T

KK

T T

O O

T T

KK

T T

O O

TT

K between T K between T -- O O -- T groups is stronger than vdwT groups is stronger than vdw


Phlogopite:Phlogopite: K MgK Mg33 [Si[Si33AlOAlO1010] (OH)] (OH)22

TT--layer layer -- tritriocathedral (Mgocathedral (Mg22++) layer ) layer -- TT--layer layer -- KK

T T

O O

T T

KK

T T

O O

T T

KK

T T

O O

TT

K between T K between T -- O O -- T groups is stronger than vdwT 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 = T -- O O -- T T -- (brucite) (brucite) -- T T -- O O -- T T -- (brucite) (brucite) -- T T -- O O -- T T --

Very hydrated (OH)Very hydrated (OH)88, so low, so low--temperature stability (lowtemperature stability (low--T metamorphism T metamorphism

and alteration of mafics as cool)and alteration of mafics as cool)


HRTEM image of anthophyllite (left) with typical doubleHRTEM image of anthophyllite (left) with typical double--chain widthchain width

Jimthompsonite (center) has tripleJimthompsonite (center) has triple--chainschains

Chesterite is an ordered alternation of doubleChesterite is an ordered alternation of double-- and tripleand triple--chainschains

anthophylliteanthophyllite jimthompsonitejimthompsonite chesteritechesterite

Fig. 6, Veblen et al (1977) Science 198 © AAAS

Disordered structures show 4Disordered structures show 4--chain widths and even a 7chain widths and even a 7--chain widthchain 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: biobiotitetite--pyrpyroxeneoxene--amphamphiboleibole))

“Biopyriboles”“Biopyriboles”Fig. 7, Veblen et al (1977)

Science 198 © AAAS

TectosilicatesTectosilicates

Stishovite

Coesite

- quartz

- quartz

Liquid

Tridymite

Cristobalite

600 1000 1400 1800 2200 2600

2

4

6

8

10

Pre

ssure

(G

Pa)

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

Tridymite

Cristobalite


High Quartz at High Quartz at 581581ooCC

001 Projection Crystal Class 622001 Projection Crystal Class 622

Stishovite

Coesite

- quartz

- quartz

Liquid

Tridymite

Cristobalite


CristobaliteCristobalite

001 Projection Cubic Structure001 Projection Cubic Structure

Stishovite

Coesite

- quartz

- quartz

Liquid

Tridymite

Cristobalite


StishoviteStishovite

High pressure High pressure SiSiVIVI

Stishovite

Coesite

- quartz

- quartz

Liquid

Tridymite

Cristobalite


Low Quartz StishoviteLow Quartz Stishovite

SiSiIVIV SiSiVIVI


FeldsparsFeldspars

Albite: Albite: NaNaAlAlSiSi33OO88

Substitute two Substitute two

AlAl3+3+ for Sifor Si4+4+

allows Caallows Ca2+2+ to to

be addedbe added

Substitute AlSubstitute Al3+3+

for Sifor Si4+4+ allows allows

NaNa++ or Kor K++ to be to be

addedadded

Thanks a lot for your Thanks a lot for your

attentionattention

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