mineral-mineral silikat

Classification of MineralsClassification of Minerals

Classification of Minerals by Chemical Composition:Classification of Minerals by Chemical Composition:

Dana's System of Mineralogy Dana's System of Mineralogy (and its derivatives)(and its derivatives)• ca. ca. 1515 major groups of minerals with a few important subgroups major groups of minerals with a few important subgroups

• named according to named according to dominant anion dominant anion or anionic groupor anionic group

• by far the most important group is the by far the most important group is the silicatessilicates

- 6 subgroups based on crystal structur- 6 subgroups based on crystal structur

• New Dana’s minerals classifiation (www.webmineral.com)New Dana’s minerals classifiation (www.webmineral.com)

MineralsMinerals

MineralsMinerals

ChemicalChemicalPropertiesProperties

OpticalOpticalPropertiesProperties

PhysicalPhysicalPropertiesProperties

chemical compositionchemical composition+ crystal structure+ crystal structure

Mineral ClassificationMineral ClassificationCRYSTAL CHEMICAL CLASSESCRYSTAL CHEMICAL CLASSES(Dana's System of Mineralogy)(Dana's System of Mineralogy)

1. 1. native elements native elements 2. 2. sulphidessulphides, arsenides, tellurides , arsenides, tellurides 3. sulphosalts3. sulphosalts4. 4. simple oxides simple oxides 5. 5. hydroxideshydroxides 6. 6. multiple oxides multiple oxides 7. 7. halideshalides 8. 8. carbonatescarbonates 9. borates 9. borates 10. 10. sulphatessulphates 11. chromates11. chromates12. 12. phosphates,phosphates, arsenates, vanadates arsenates, vanadates 13. vanadium oxysalts 13. vanadium oxysalts 14. molybdates, tungstates 14. molybdates, tungstates 15. 15. SILICATESSILICATES: : 6 different subclasses based on crystal structure6 different subclasses based on crystal structure

Behavior of elements: Goldschmidt’s classification

Elements divided into four broad categories:

Lithophile • generally found within crust and

mantle

• Concentrate in silica-rich melts

Siderophile • Generally concentrate in iron-

rich melt

Chalcophile• Generally occurs with sulfur

Atmophile • Generally found in the

atmosphere

Most Common Elements of Earth’s Crust

Oxygen:Oxygen: OO-2-2

Silicon:Silicon: SiSi+4+4

Aluminum:Aluminum: AlAl+3+3

Iron:Iron: FeFe+2 or +3+2 or +3

Calcium: CaCalcium: Ca+2+2

Sodium: NaSodium: Na+1+1

Potassium: KPotassium: K+1+1

Magnesium: MgMagnesium: Mg+2+2

Plate tectonics: Mixing crust and mantle

Reference book: This Dynamic Earth by USGS Reference book: This Dynamic Earth by USGS http://pubs.usgs.gov/publications/text/dynamic.hthttp://pubs.usgs.gov/publications/text/dynamic.htmlml

Earth’s crust and mantle are rich in lithophile elements (those that concentrate in a silica-rich melt)

AllAll types of magma contain silicon and types of magma contain silicon and oxygen as silica (SiO2) in different oxygen as silica (SiO2) in different amountsamounts (~40 -70%) (~40 -70%)

Igneous rocks are almost exclusively Igneous rocks are almost exclusively made up of SILICATE minerals made up of SILICATE minerals Containing the (SiO4)Containing the (SiO4)-4-4 anionic group anionic group

Silicate minerals

• Contain the (SiO4)-4 anionic group

• Make up 95% of the continental crust, and almost all of the oceanic crust and the mantle

Mineral GroupsMineral Groups

FerromagnesianFerromagnesianSilicates (Fe, Mg)Silicates (Fe, Mg)

Non-ferromagnesianNon-ferromagnesianSilicates (K, Na, Ca, Al)Silicates (K, Na, Ca, Al)

OxidesOxidesCarbonatesCarbonatesSulfides/sulfatesSulfides/sulfatesNative elementsNative elements

1515

Silicate NomenaclatureSilicate Nomenaclature

Silicate Subclass Alternative Name

Neso – (or Ortho) Silicates

Island

Sorosilicates Couplet

Cyclosilicates Ring

Inosilicates Chain

Phyllosilicates Layer

Tectosilicates (or Tekto-) Framework

Element of Mineral Silicates StructureElement of Mineral Silicates Structure

Silicate tetrahedron: Silicate tetrahedron: the single most important structural elementthe single most important structural element in mineralsin minerals

Nesse Fig. 11.1Nesse Fig. 11.1[SiO[SiO44]]4-4-

space-fillingspace-fillingviewview

expandedexpanded("stick")("stick")

viewview

co-ordinationco-ordinationpolyhedronpolyhedron

top top viewview

basal basal viewview

schematic:schematic:

1717

Sharing of Oxygen AnionsSharing of Oxygen Anions

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 Nesosilicates/ OthosilocatesNesosilicates/ Othosilocates

Examples: olivine garnetExamples: olivine garnet

[Si[Si22OO77]]6-6- Double tetrahedra Double tetrahedra Sorosilicates/ DisilicatesSorosilicates/ Disilicates

Examples: lawsoniteExamples: lawsonite

n[SiOn[SiO33]]2-2- n = 3, 4, 6 n = 3, 4, 6 Cyclosilicates/ Ring SilicatesCyclosilicates/ Ring Silicates

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 Phyllosilicates/ Sheet SilicatesPhyllosilicates/ Sheet Silicates

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 Tectosilicates/ Tectosilicates/ Framework Silicates Framework Silicates

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

low-quartzlow-quartz

NesosilicatesNesosilicates

Characterized by independent Si0Characterized by independent Si04 4 tetrahedra, tetrahedra, which are not linked together directlywhich are not linked together directly

They are bonded together by ionic bonds to They are bonded together by ionic bonds to interstitial cationsinterstitial cations

The structures of the nesosilicates are therefore, The structures of the nesosilicates are therefore, very dependent on the size and charge of the very dependent on the size and charge of the interstitial cationsinterstitial cations

Because the tetrahedral do not share oxygen, the Because the tetrahedral do not share oxygen, the Si:0 ratio is 1:4.Si:0 ratio is 1:4.

Interstitial CationsInterstitial Cations

Since the SiOSince the SiO44 tetrahedron has a charge of 4, tetrahedron has a charge of 4,

two divalent cations, a trivalent and a two divalent cations, a trivalent and a monovalent, or a quadravalent cation are monovalent, or a quadravalent cation are required to maintain electrical neutrality required to maintain electrical neutrality

Several structure types are possible – in the Several structure types are possible – in the silicate structures the letter A = non-silicon silicate structures the letter A = non-silicon cations with lower valency then Sications with lower valency then Si4+4+ , B = Si or , B = Si or Al or other higher valent cations, O = oxygenAl or other higher valent cations, O = oxygen

Mineral StructuresMineral StructuresNesosilicates: independent SiONesosilicates: independent SiO44 tetrahedra tetrahedra

Olivine Structure: (Mg,Fe)Olivine Structure: (Mg,Fe)22SiOSiO44

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

Representing mineral structures:Representing mineral structures:

olivine:olivine:MgMg22SiOSiO44

(orthosilicate)(orthosilicate)Nesse Fig 4.9Nesse Fig 4.9

MgMg2+2+

OO2-2-

SiSi4+4+

atomic atomic radius (Ǻ) CNradius (Ǻ) CN

MgMg2+2+ 0.720.72SiSi4+4+ 0.260.26OO2-2- 1.401.40

space-filling viewspace-filling view expanded (stick) viewexpanded (stick) view





MgMg2+2+ 0.720.72 6 6SiSi4+4+ 0.260.26 4 4OO2-2- 1.401.40

co-ordination polyhedraco-ordination polyhedrapolyhedra + stickspolyhedra + sticks

tetrahedratetrahedra

octahedraoctahedraMgMg2+2+

SiOSiO4-4-





MgMg2+2+ 0.720.72 6 6SiSi4+4+ 0.260.26 4 4OO2-2- 1.401.40

distances between atoms distances between atoms shown as %shown as %

unit cell dimensionsunit cell dimensions

(distances along a, b, c(distances along a, b, ccrystallographic axes)crystallographic axes)

0 = bottom0 = bottom100 = top100 = top

50 = half-way50 = half-way

Look familiar?Look familiar? OlivineOlivine

Light to dark greenLight to dark green Really hard (6.5-7)Really hard (6.5-7)

Olivine SeriesOlivine Series

Olivine itself is the compound (Fe, Mg)Olivine itself is the compound (Fe, Mg)22 Si0 Si044 with a with a

complete solid solution seriescomplete solid solution series As with other solid solution series the two end As with other solid solution series the two end

members are the most importantmembers are the most important Fayalite – FeFayalite – Fe22Si0Si044 Fa Fa

Forsterite – MgForsterite – Mg22Si0Si044 Fo Fo

Olivine Solid Solution RangesOlivine Solid Solution Ranges

ForsteriteForsterite 0-10% Fe0-10% Fe ChrysoliteChrysolite 10-30% Fe10-30% Fe HyalosideriteHyalosiderite 30-50% Fe30-50% Fe MortonoliteMortonolite 50-70% Fe50-70% Fe FerrohortonoliteFerrohortonolite 70-90% Fe70-90% Fe FayaliteFayalite 90-100% Fe90-100% Fe

Solid Solution NomenclatureSolid Solution Nomenclature

As with some other important series an As with some other important series an abbreviation is used for the end members – abbreviation is used for the end members – compositions can be expressed using compositions can be expressed using abbreviated symbolsabbreviated symbols

Example FeExample Fe0.60.6MgMg1.41.4Si0Si044 = Fa = Fa3030 Fo Fo7070

Other Olivine Group MineralsOther Olivine Group Minerals

CaMgSi0CaMgSi04 4 Monticellite Monticellite

MnMn22Si0Si044 Tephroite Tephroite

CaMnSi0CaMnSi044 Glaucochroite Glaucochroite

CaFeSi0CaFeSi044 Kirschsteinite Kirschsteinite


Olivine Occurrences:Olivine Occurrences: Principally in mafic and ultramafic igneous and meta-igneous Principally in mafic and ultramafic igneous and meta-igneous

rocksrocks Fayalite (FeFayalite (Fe22SiOSiO44) in meta-ironstones and in some alkalic ) in meta-ironstones and in some alkalic

granitoidsgranitoids Forsterite (MgForsterite (Mg22SiOSiO44) in some siliceous dolomitic marbles) 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

Garnets, AGarnets, A33BB22(SiO(SiO44))33

Larger A site is occupied by divalent Larger A site is occupied by divalent cations which are relatively large, with a cations which are relatively large, with a coordination number of VIIIcoordination number of VIII Typical cations are CaTypical cations are Ca2+2+, Mg, Mg2+2+, Fe, Fe2+2+, Mn, Mn2+2+, and , and

some trivalent lanthanidessome trivalent lanthanides The smaller B site is occupied by trivalent The smaller B site is occupied by trivalent

cations which are smaller, with a CN of VIcations which are smaller, with a CN of VI Typical cations A1Typical cations A13+3+, Cr, Cr3+3+, Fe, Fe3+3+, and Ti, and Ti4+4+

Calcium and Noncalcium Calcium and Noncalcium GarnetsGarnets

CaCa2+2+ is larger than Mg is larger than Mg2+2+, Fe, Fe2+2+ and Mn and Mn2+2+ Garnets can be split into two groups, the Ca Garnets can be split into two groups, the Ca

and non-Ca garnetsand non-Ca garnets A similar division may be made for the B A similar division may be made for the B

ions into A1, Feions into A1, Fe3+3+ and Cr and Cr3+3+ garnets. garnets.

Ca GarnetsCa Garnets

Name Formula Color

Uvarovite Ca3Cr2(Si04)3 Emerald green

Grossularite, also called cinnamon stone, essonite

Ca3A12(Si04)3 White green, yellow, cinnamon brown, pale red

Andradite Ca3Fe2(Si04)3 Yellow, green, brown, black

Non-Ca GarnetsNon-Ca Garnets

Name Formula Color

Pyrope Mg3A12(Si04)3 Deep red to black

Almandine Fe3A12(Si04)3 Deep red to brown

Spessartite Mn3A12(Si04)3 Brownish to red

Garnet PhotosGarnet Photos

Uvarovite Garnet (above)Uvarovite Garnet (above)

Grossular garnet (above)Grossular garnet (above)

Grossular, variety hessonite (left)Grossular, variety hessonite (left)

Garnet PhotosGarnet Photos

Andradite Andradite garnet (above)garnet (above)

Almandine garnetAlmandine garnet(left and right)(left and right)

GarnetGarnet

CaCa33AlAl22(SiO(SiO44))33

AluminosilicatesAluminosilicates

Aluminosilicates have aluminum in Aluminosilicates have aluminum in addition to silicon in the structureaddition to silicon in the structure

They may belong to any silicate subclassThey may belong to any silicate subclass

AlAl22SiOSiO55

PolymorphsPolymorphs Kyanite, Kyanite,

andalusite, and andalusite, and sillimaite have sillimaite have the same the same chemistry, but chemistry, but form under form under different P and T different P and T conditionsconditions

AlAl22SiOSiO5 5 StructuresStructures

TopazTopaz

A1A122 (Si0 (Si044)(F, OH))(F, OH)22

H = 8 H = 8 {001} perfect{001} perfect Used as a gem stoneUsed as a gem stone

StauroliteStaurolite

FeFe22A1A1990066(Si0(Si044))44(O,OH)(O,OH)22

Crystals are prismaticCrystals are prismatic Often twinned (penetration twins), Often twinned (penetration twins),

with two varieties of cruciform with two varieties of cruciform twinstwins

TitaniteTitanite

CaTiO(Si0CaTiO(Si044) ) Formerly known as Formerly known as

sphenesphene An example of a An example of a

titanosilicatetitanosilicate N = 1.91 – luster N = 1.91 – luster

resinous to adamantineresinous to adamantine

5454

WillimiteWillimite ZnZn22SiOSiO44

Associated with other Associated with other Zn oresZn ores

Mn may replace ZnMn may replace Zn Often fluorescenceOften fluorescence

Willemite with Franklinite Willemite with Franklinite and Quartzand QuartzNew Jersey New Jersey

SorosilicatesSorosilicates

Characterized by two Si0Characterized by two Si04 4 tetrahedra joined tetrahedra joined

through a single oxygen to give an Si:O through a single oxygen to give an Si:O ratio of 2:7ratio of 2:7

Nesse Fig. 11.2Nesse Fig. 11.2

schematic schematic disilicate disilicate structure structure (e.g., epidote)(e.g., epidote)

1 shared oxygen1 shared oxygenhow many Si atoms? 2 how many O atoms? 7how many Si atoms? 2 how many O atoms? 7

chemical formula? [Sichemical formula? [Si22OO77] net charge? -6] net charge? -6

SorosilicatesSorosilicates

Epidote GroupEpidote Group

Contains both Si0Contains both Si044 and Si and Si220077

groupsgroups General formula is General formula is

XX22VIIIVIIIYY33

VIVI(Si0(Si044)O(OH))O(OH) X = CaX = Ca2+2+, Na, Na++

Y = A1Y = A13+3+, Fe, Fe3+3+, Mn, Mn3+3+, Cr, Cr3+3+

• Epidote: CaEpidote: Ca22(A1,Fe)A1(A1,Fe)A122O(SiO(Si22OO77)(SiO)(SiO44)(OH))(OH)

• Clinozoisite: CaClinozoisite: Ca22A1A133O (SiO (Si22OO77)(SiO)(SiO44)(OH))(OH)

VesuvianiteVesuvianite Formerly called Formerly called

IdocraseIdocrase CaCa1010(Mg, (Mg,

Fe)Fe)22A1A144(Si0(Si044))55(Si(Si220077))22((

OH)OH)77

Tetragonal H = 6 ½ Tetragonal H = 6 ½ Brown or greenBrown or green

HemimorphiteHemimorphite ZnZn44(Si(Si220077)(OH))(OH)22HH220 is 0 is

one mineral of the one mineral of the sorosilicate group with sorosilicate group with isolated Siisolated Si220077 groups, groups, cross linked by Zn cross linked by Zn cationscations

Formed as a secondary Formed as a secondary mineral in the mineral in the oxidized portions of oxidized portions of zinc depositszinc deposits

LawsoniteLawsonite

CaA1CaA122(OH)(OH)22SiSi22OO77HH22OO Found only in metamorphic Found only in metamorphic

blue (glaucophane)-schist or blue (glaucophane)-schist or similar low temperature, similar low temperature, moderate to high pressure moderate to high pressure environments. environments.

CyclosilicatesCyclosilicates

When three or more Si tetrahedral groups When three or more Si tetrahedral groups are linked, a cyclical structure is possibleare linked, a cyclical structure is possible

The Si:O ratio is 1:3The Si:O ratio is 1:3 Rings containing 3, 4, or 6 Si are possible, Rings containing 3, 4, or 6 Si are possible,

but only the rings with 6 Si are at all but only the rings with 6 Si are at all commoncommon

Cyclic SilicatesCyclic Silicates

3 membered ring3 membered ring6 membered rings6 membered rings

Beryl StructureBeryl Structure

Yellow Si tetrahedra are in the upper layer, the green ones in the lower layerYellow Si tetrahedra are in the upper layer, the green ones in the lower layer The outer points of the tetrahedra are actually edges viewed along their lengthThe outer points of the tetrahedra are actually edges viewed along their length Purple tetrahedra contain Be and are viewed down their four-fold inversion Purple tetrahedra contain Be and are viewed down their four-fold inversion

axesaxes They connect the bottom corners of the tetrahedra in the upper ring with the top They connect the bottom corners of the tetrahedra in the upper ring with the top

corners of the tetrahedra in the lower ring corners of the tetrahedra in the lower ring Solitary blue atoms are Al, in VI-fold coordination with the adjacent tetrahedral Solitary blue atoms are Al, in VI-fold coordination with the adjacent tetrahedral

oxygensoxygens

A single unit cell of berylA single unit cell of beryl

Complete Beryl LatticeComplete Beryl Lattice

Shows the octahedral coordination of Al in blueShows the octahedral coordination of Al in blue

Gem BerylGem Beryl•Upper left, emeraldUpper left, emerald•Lower left, Lower left, morganite morganite •Upper right, Upper right, aquamarineaquamarine•Lower right, golden Lower right, golden berylberyl

Tourmaline Tourmaline

• Elbaite, a gem varietyElbaite, a gem varietyof tourmalineof tourmaline

• Schorl crystal, with Schorl crystal, with Striations, typical of Striations, typical of tourmalinetourmaline

ChrysocollaChrysocolla

Amorphous but Amorphous but similar to dioptase, a similar to dioptase, a six-membered six-membered cyclosilicatecyclosilicate

May contain SiMay contain Si44OO1010

units, which would units, which would make it a make it a phyllosilicatephyllosilicate

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

OrthopyroxenesOrthopyroxenes

Enstatite Enstatite MgSiOMgSiO33

Hypersthene Hypersthene (Mg, Fe)SiO(Mg, Fe)SiO33

OrthoferrosiliteOrthoferrosilite Fe SiO Fe SiO3 3

EnstatiteEnstatite

Brownish Brownish orthopyroxene (opx)orthopyroxene (opx)

Lower photo is of Lower photo is of Bronzite, an opx Bronzite, an opx containing some Fe, containing some Fe, and displaying an and displaying an iridescence known as iridescence known as Schiller lusterSchiller luster

ClinopyroxenesClinopyroxenes

X YX Y

Diopside Diopside Ca Ca Mg Mg SiSi22OO66

Hedenbergite Hedenbergite CaCa Fe Fe2+2+ SiSi22OO66

AugiteAugite CaCa (Mg, Fe (Mg, Fe2+2+) (Al, Fe) (Al, Fe3+3+, Ti), Ti) SiSi22OO66

PigeonitePigeonite (Mg,Fe (Mg,Fe2+2+, Ca) (Mg, Fe, Ca) (Mg, Fe2+2+) (Al, Fe) (Al, Fe3+3+)) SiSi22OO66

AegirineAegirine NaNa Fe Fe3+3+ SiSi22OO66

JadeiteJadeite Na Na Al Al SiSi22OO66

SpodumeneSpodumene LiLi Al Al SiSi22OO66

AugiteAugite

Augite is distinguished Augite is distinguished by 2D cleavage @ 90by 2D cleavage @ 90°°

Al occurs at Al occurs at tetrahedral sites, so tetrahedral sites, so trivalent cations are trivalent cations are present at normally present at normally divalent sitesdivalent sites

Pyroxene “Quad”Pyroxene “Quad”

The pyroxene quadrilateral The pyroxene quadrilateral forms part of a larger ternary forms part of a larger ternary system (CaSiOsystem (CaSiO33-MgSiO-MgSiO33--FeSiO3), that includes another FeSiO3), that includes another single chain silicate single chain silicate wollastonitewollastonite

The Ca-rich clinopyroxenes are The Ca-rich clinopyroxenes are separated from the separated from the orthopyroxenes, and from the orthopyroxenes, and from the Ca-poor clionpyroxene Ca-poor clionpyroxene pigeonite by a solvus (shown in pigeonite by a solvus (shown in green in the figure) green in the figure)


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

(Ca,Mg,Fe,Al)(Ca,Mg,Fe,Al) 2 2 (Si, Al) (Si, Al)22OO66

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

Pyroxene vs. Pyroxene vs. PyroxenoidPyroxenoid

““Ideal” pyroxene Ideal” pyroxene chains with 5.2 chains with 5.2 Å Å repeat (2 tetrahedra) repeat (2 tetrahedra) become distorted as become distorted as other cations occupy other cations occupy VI sitesVI sites

Note presence of SiNote presence of Si22OO77 coupletscouplets

7.1 A7.1 A

5.2 A5.2 A

12.5 A12.5 A

PyroxenePyroxene2-tet repeat2-tet repeat

WollastoniteWollastonite (Ca (Ca M1) M1) 3-tet repeat3-tet repeat

RhodoniteRhodoniteMnSiO3MnSiO3 5-tet repeat5-tet repeat

PyroxenoidsPyroxenoids

Top, pectoliteTop, pectolite Middle, wollastoniteMiddle, wollastonite Bottom, rhodoniteBottom, rhodonite

Amphibole ChainAmphibole Chain

Double chain of Double chain of SiOSiO44 tetrahedra tetrahedra

connected by connected by corner sharing corner sharing

100100

Amphibole StructureAmphibole Structure

Amphiboles have a double chain structure Amphiboles have a double chain structure formed by sharing three cornersformed by sharing three corners

All have the basic SiAll have the basic Si44OO1111 double chains, double chains,

with larger X ions are in VIII coordination, with larger X ions are in VIII coordination, while smaller Y cations are in VI while smaller Y cations are in VI coordinationcoordination

Si:O = 1:2.75Si:O = 1:2.75

101101

Amphibole FormulaAmphibole Formula

The general formula is:The general formula is: WW0-10-1XX0-70-7YY7-147-14ZZ1616OO4444(OH)(OH)44

X: NaX: Na++, Ca, Ca2+2+, minor K, minor K++, Mn, Mn2+2+, Fe, Fe2+2+, Mg, Mg2+2+, Li, Li++

Y: MgY: Mg2+2+, Fe, Fe2+2+, Fe, Fe3+3+, Al, Al3+3+, Mn, Mn2+2+, Mn, Mn3+3+, Ti, Ti4+4+

Z: SiZ: Si4+4+, Al, Al3+3+

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


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)


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)

Pyroxene CleavagePyroxene Cleavage

• Aegirine – a sodic pyroxeneAegirine – a sodic pyroxene

Amphibole CleavageAmphibole Cleavage

HornblendeHornblende

Look familiar?Look familiar? Hornblende:Hornblende:

striated appearance striated appearance hexagonal cross-hexagonal cross-

section section Dark-dark green to Dark-dark green to

blackblack

OrthoamphiboleOrthoamphibole

Orthoamphibole X,YOrthoamphibole X,Y ZZ

Anthopyllite (Mg, Fe2+)Anthopyllite (Mg, Fe2+)77 (Si(Si88OO2222) (OH, F)) (OH, F)22

ClinoamphibolesClinoamphibolesClinoamphiboles W X,Y Z

Cummingtonite Fe2+5Mg2 (Si8O22)(OH, F)2

Grunerite Fe7 (Si8O22)(OH, F)2

Tremolite Ca2Mg5 (Si8O22)(OH, F)2

Actinolite Ca2(Mg,Fe2+)5 (Si8O22)(OH, F)2

Hornblende (Na,K)0-1 (Ca,Na)2 (Mg, Fe2+, Al, Fe3+)5

{(A1, Si)2Si6O22}(OH,F)2

Glaucophane Na2 Mg3 Al2 Si8 O22 (OH)2

Riebeckite Na2 Fe32+Fe2

3+ (Si8O22)(OH, F)2

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

Sheet Silicates Sheet Silicates (Nesse, Ch.13, p.235-39; 244-48)(Nesse, Ch.13, p.235-39; 244-48)

photos: mindat.orgphotos: mindat.org

muscovitemuscovite biotitebiotite

lepidolitelepidolite

phlogopitephlogopite

http://www.mindat.org/min-207.html

sheet silicate, general formula: AYsheet silicate, general formula: AY2-32-3TT44OO1010(OH)(OH)22

where A = K,Na; Y = Al,Mg,Fe,Mn,Ti; T = Al,Siwhere A = K,Na; Y = Al,Mg,Fe,Mn,Ti; T = Al,Si

two structural groupstwo structural groups of mica are recognised of mica are recognised depending on number of octahedral (Y) sites:depending on number of octahedral (Y) sites:

dioctahedral micas:dioctahedral micas: Y = 2Y = 2 (e.g., muscovite, paragonite) (e.g., muscovite, paragonite) Y-site occupied by trivalent cations (mainly AlY-site occupied by trivalent cations (mainly Al3+3+)) “ “root” formula: muscovite = KAlroot” formula: muscovite = KAl22AlSiAlSi33OO1010(OH)(OH)22

trioctahedral micas:trioctahedral micas: Y = 3 Y = 3 (e.g., biotite, lepidolite)(e.g., biotite, lepidolite) Y-site occupied by divalent cations (mainly Mg,Fe)Y-site occupied by divalent cations (mainly Mg,Fe) “ “root” formula: phlogopite = KMgroot” formula: phlogopite = KMg33AlSiAlSi33OO1010(OH)(OH)22

Sheet Silicates Sheet Silicates Nesse, Ch.13, p.235-39; 244-48)Nesse, Ch.13, p.235-39; 244-48)

[SiO[SiO44]]4-4- sheet (T-site) sheet (T-site)

octahedral Y-sitesoctahedral Y-siteswith OH- at apiceswith OH- at apices

TTOOTT

““II-beam”-beam”

Sheet SilicatesSheet Silicates(Nesse, Ch.13, p.235-39; 244-48)(Nesse, Ch.13, p.235-39; 244-48)


top view of octahedral layertop view of octahedral layer(light grey)(light grey)with superimposed T-layerwith superimposed T-layer(dark grey; note 6-fold symmetry)(dark grey; note 6-fold symmetry)

apical oxygen in T-layer replacesapical oxygen in T-layer replacesOH- group in O-layerOH- group in O-layer

linking O-layers and T-layerslinking O-layers and T-layers

forms OT or TOT (forms OT or TOT (II-beam) structures-beam) structures

OHOH

OOTT

OO

TT

Sheet SilicatesSheet Silicates(Nesse, Ch.13, p.235-39; 244-48)(Nesse, Ch.13, p.235-39; 244-48)


octahedral Y-sitesoctahedral Y-siteswith OH- at apiceswith OH- at apices

trioctahedral:trioctahedral: 3/3 of Y-sites filled3/3 of Y-sites filled divalent cations (Mg, Fedivalent cations (Mg, Fe2+2+, Mn), Mn)

dioctahedral:dioctahedral: 2/3 of Y-sites filled 2/3 of Y-sites filled trivalent cations (Altrivalent cations (Al3+3+, Cr, Cr3+3+, Fe, Fe3+3+))

trioctahedraltrioctahedral

dioctahedraldioctahedral

TTOOTT

““II-beam”-beam”

Sheet Silicates Sheet Silicates (Nesse, Ch.13, p.235-39; 244-48)(Nesse, Ch.13, p.235-39; 244-48)


OOTT

TOTOkaolinitekaoliniteserpentineserpentine

TOTTOTpyrophyllitepyrophyllitetalctalc

TOTTOT + cation + cationmicasmicas

TOT + OTOT + Ochloritechlorite

linking O-layers and T-layerslinking O-layers and T-layers

forms OT or TOT (forms OT or TOT (II-beam) structures-beam) structures

OT or TOT structures linked by:OT or TOT structures linked by: van der Waals bondsvan der Waals bonds (weak)(weak)

extra O layersextra O layers (a little stronger)(a little stronger)

large cationslarge cations (a little stronger)(a little stronger)

type of linkage determines type of linkage determines type of sheet silicatetype of sheet silicate

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


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

Other Sheet Silicates Other Sheet Silicates (Nesse, Ch. 13 p. 235-44; 252-57)(Nesse, Ch. 13 p. 235-44; 252-57)


serpentineserpentine

chrysotilechrysotile

lizarditelizardite

clay mineralsclay minerals

kaolinitekaolinite

illiteillite

talctalcchloritechlorite



Other Sheet Silicates Other Sheet Silicates (Nesse, Ch. 13 p. 235-44; 252-57)(Nesse, Ch. 13 p. 235-44; 252-57)

Clay minerals:Clay minerals: group of very fine-grained (< 2 group of very fine-grained (< 2 m) sheet silicatesm) sheet silicates

kaolinitekaolinite

illiteillite

kaolinitekaolinite

too fine-grained to be distinguished bytoo fine-grained to be distinguished byconventional optical or physical testsconventional optical or physical tests

identification requires a combination ofidentification requires a combination ofXRD and electron microscopy methodsXRD and electron microscopy methods

dominant constituent of “clay” (fine-dominant constituent of “clay” (fine-grained sediment)grained sediment)

characterised by high Al, OH contentscharacterised by high Al, OH contentsin addition to Si and other cationsin addition to Si and other cations

varieties include: kaolinite, smectite, varieties include: kaolinite, smectite, illite, vermiculite, chloriteillite, vermiculite, chlorite

Other Sheet Silicates Other Sheet Silicates (Nesse, Ch. 13 p.252-57)(Nesse, Ch. 13 p.252-57)

Clay minerals:Clay minerals: group of very fine-grained (< 2 group of very fine-grained (< 2 m) sheet silicatesm) sheet silicates

AlAl22SiSi22OO55(OH)(OH)44

KK0.50.5AlAl22(Al(Al0.80.8SiSi3.23.2)O)O1010(OH)(OH)44

““muscovite-like”muscovite-like”

CaCa0.20.2(Al,Mg,Fe)(Al,Mg,Fe)22(Al,Si)(Al,Si)44OO1010(OH)(OH)22.nH.nH22OO

(Mg,Fe,Al)(Mg,Fe,Al)66

(Si,Al)(Si,Al)44OO1010(OH)(OH)88

mixed layermixed layerclaysclays

expandable clayexpandable clay


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)


Framework Silicates/ Framework Silicates/ TectosilicatesTectosilicates

The tectosilicates are three – dimensional, The tectosilicates are three – dimensional, or framework, silicatesor framework, silicates

They involve linkage of SiOThey involve linkage of SiO44 tetrahedra tetrahedra

through all four oxygen atomsthrough all four oxygen atoms The resulting structure is stable and The resulting structure is stable and

strongly bonded strongly bonded Si:O ratio is 1:2Si:O ratio is 1:2

a framework silicate with the formula: a framework silicate with the formula: SiOSiO22

by far the most abundant silica group mineral isby far the most abundant silica group mineral is

-quartz-quartz

other SiOother SiO22 polymorphspolymorphs are preserved are preserved

in the geological recordin the geological recordunder special circumstancesunder special circumstances

a number of a number of non- non- or or micro-crystallinemicro-crystalline varieties varietiesof SiOof SiO2 2 also form important “minerals”also form important “minerals”

MoW 7: MoW 7: Silica Group Silica Group (Nesse, Ch. 12, p. 201-208)(Nesse, Ch. 12, p. 201-208)

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.

Silica Group Silica Group (Nesse, Ch. 12, p. 201-208)(Nesse, Ch. 12, p. 201-208)

ultra-high pressureultra-high pressure(UHP) conditions(UHP) conditions

phase diagram for SiOphase diagram for SiO22 system system

ultra-high temperatureultra-high temperature(UHT) conditions(UHT) conditions

certain SiOcertain SiO22

polymorphspolymorphsindicate specificindicate specificP-T ranges andP-T ranges andgeologicalgeologicalenvironmentsenvironments


CoesiteCoesitediagnostic of UHP metamorphismdiagnostic of UHP metamorphism(continental subduction)(continental subduction)

phase diagram for SiOphase diagram for SiO22 system system

-quartz -quartz -quartz transformation always-quartz transformation alwaystakes place; takes place; -quartz not stable at surface-quartz not stable at surface

restricted to impact cratersrestricted to impact craters

restricted to volcanic environmentsrestricted to volcanic environments

non- non- oror micro-crystalline micro-crystalline varieties of SiO varieties of SiO22


non-crystalline:non-crystalline: opalopal - a form of - a form of colloidalcolloidal silica silica - important gemstone- important gemstone

microcrystalline:microcrystalline: moganitemoganite – alternating sheets of right- – alternating sheets of right-

and left-handed and left-handed -quartz-quartz chert chert (including jasper, flint)(including jasper, flint)

microcrystalline, granularmicrocrystalline, granular chalcedonychalcedony (including agate) (including agate)

microcrystalline, fibrousmicrocrystalline, fibrous

Varieties of Varieties of Crystalline QuartzCrystalline Quartz

BlueBlue AmethystAmethyst

CitrineCitrine

MilkyMilky

RoseRose

Varieties of Varieties of Cryptocrystalline Cryptocrystalline

QuartzQuartzJasperJasper ChalcedonyChalcedony

ChertChert ChrysopraseChrysoprase


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

FeldsparsFeldspars

Alkali – Potassium and AbAlkali – Potassium and Ab95-10095-100

Plagioclase AnPlagioclase An5-1005-100

Barium Barium Celsian BaAlCelsian BaAl22SiSi22OO88

Hyalophane (K, Ba)(A1,Si)Hyalophane (K, Ba)(A1,Si)22SiSi22OO88

MoW 3: MoW 3: Feldspar Feldspar (Nesse, Ch. 12, p. 208-225)(Nesse, Ch. 12, p. 208-225)


Perthite


Feldspar Feldspar CompositionComposition

Alkali FeldsparsAlkali Feldspars

K-spar shows a variety of polymorphic K-spar shows a variety of polymorphic formsforms SanidineSanidine OrthoclaseOrthoclase MicroclineMicrocline

SanidineSanidineOrthoclaseOrthoclaseMicroclineMicrocline

Perthite and AntiperthitePerthite and Antiperthite

Albite in K-spar host = perthiteAlbite in K-spar host = perthite K-spar in plagioclase host = antiperthiteK-spar in plagioclase host = antiperthite

PerthitePerthite

Plagioclase NamePlagioclase Name

Plagioclases are triclinic Plagioclases are triclinic Their a-b and b-c angles are a bit more Their a-b and b-c angles are a bit more

oblique than microclineoblique than microcline Hence the name: Hence the name: plagio-plagio-, oblique and , oblique and claseclase, ,

breakbreak

AlbiteAlbite

Plagioclase FeldsparsPlagioclase Feldspars AlbiteAlbite

AnAn0-100-10 - - Found only in very sodic rocks, hence usually metamorphic or formed in Found only in very sodic rocks, hence usually metamorphic or formed in marine conditions as a sedimentary cement, or by ion exchange with more calcic marine conditions as a sedimentary cement, or by ion exchange with more calcic plagioclase.plagioclase.

OligoclaseOligoclase AnAn10-30 10-30 - The dominant plagioclase in granitic rocks- The dominant plagioclase in granitic rocks

AndesineAndesine AnAn30-5030-50 - - Found in intermediate igneous rocks Found in intermediate igneous rocks

LabradoriteLabradorite AnAn50-70 50-70 -- The dominant plagioclase in gabbro and basalt. Also, despite their name, The dominant plagioclase in gabbro and basalt. Also, despite their name,

most anorthosites are made up of labradorite.most anorthosites are made up of labradorite. BytowniteBytownite

AnAn70-9070-90 - - The rarest. Requires both a lot of calcium and also significant sodium. The rarest. Requires both a lot of calcium and also significant sodium. Most igneous settings have too much sodium, most calc-silicate metamorphic Most igneous settings have too much sodium, most calc-silicate metamorphic settings have too little sodium.settings have too little sodium.

AnorthiteAnorthite AnAn90-100 90-100 -- Generally a metamorphic mineral in calc-silicate rocks. Generally a metamorphic mineral in calc-silicate rocks.

a framework silicate with the general formula: ATa framework silicate with the general formula: AT44OO88

where A = Ca, Na, K; T = Al, Siwhere A = Ca, Na, K; T = Al, Si

2 solid solution series:2 solid solution series:

plagioclase:plagioclase: CaAl CaAl22S1S122OO88 NaAlSi NaAlSi33OO88

anorthite (An) albite (Ab)anorthite (An) albite (Ab)

alkali feldspar:alkali feldspar: NaAlSi NaAlSi33OO88 KAlSi KAlSi33OO88

albite (Ab) orthoclase (Or)albite (Ab) orthoclase (Or)


AnAn0-100-10: albite: albite AnAn50-7050-70: labradorite: labradorite

AnAn10-3010-30 : oligoclase : oligoclase AnAn70-9070-90: bytownite: bytownite

AnAn30-5030-50: andesine: andesine AnAn90-10090-100: anorthite: anorthite

OrOr100-35100-35: orthoclase: orthoclase Or Or35-1035-10: anorthoclase: anorthoclase OrOr10-010-0: albite: albite

3 K-feldspar3 K-feldspar polymorphspolymorphs: sanidine, orthoclase, microcline: sanidine, orthoclase, microcline (high T (high T low T) low T)



Feldspar Feldspar (Nesse, Ch. 12, p. 208-225)(Nesse, Ch. 12, p. 208-225)

feldspar nomenclature feldspar nomenclature and solid-solution limitsand solid-solution limits

very limited solid soutionvery limited solid soutionbetween K- and Ca-between K- and Ca-end membersend members

OrOr100100

AnAn100100AbAb100100

AnAn10-30 10-30 An An30-5030-50 An An50-7050-70 An An70-9070-90

OrOr 10

-35

10-3

5

OrOr 35

-100

35-1

00




crystal structurecrystal structureof feldsparof feldspar

[SiO[SiO44]]4-4- groups groups

T site (Al, Si)T site (Al, Si)

““crankshaft” crankshaft” arrangementarrangement

““crankshafts” linked by A-site cationscrankshafts” linked by A-site cationsK, Na, Ca (CN = 9)K, Na, Ca (CN = 9)


orderingordering in feldspar structure in feldspar structure

both Si and Al occupy tetrahedral (T) sitesboth Si and Al occupy tetrahedral (T) sites(3:1 in K-Na- feldspar, 2:1 in Ca-plag)(3:1 in K-Na- feldspar, 2:1 in Ca-plag)

at high T, at high T, randomrandom distribution of Si, Al: distribution of Si, Al:““disordereddisordered” – ” – monoclinicmonoclinic symmetry symmetry(sanidine, orthoclase)(sanidine, orthoclase)at low T, at low T, non-randomnon-random distribution of Si, Al: distribution of Si, Al:““orderedordered” – ” – triclinic triclinic symmetrysymmetry(microcline)(microcline)

25% Al, 75% Si25% Al, 75% Si

50% Al, 50% Si50% Al, 50% Si

100% Al100% Al

100% Si100% Si

incr

easi

ng o

rder

incr

easi

ng o

rder

incr

easi

ng o

rder

,in

crea

sing

ord

er,

decr

easi

ng T

decr

easi

ng T

sanidinesanidine

orthoclaseorthoclase

microclinemicrocline

3 K-feldspar3 K-feldsparpolymorphspolymorphsdistinguisheddistinguishedby degree ofby degree ofordering of Si, Alordering of Si, Alin crystal latticein crystal lattice


twinningtwinning in feldspar in feldspar

Nesse, Fig. 12.11Nesse, Fig. 12.11

a) albite twins: reflection on (010) a) albite twins: reflection on (010) (polysynthetic or “barcode” twinning in plag)(polysynthetic or “barcode” twinning in plag)

b) pericline twins: rotation on [010]b) pericline twins: rotation on [010] (also very common in plagioclase)(also very common in plagioclase)

c) Carlsbad twins: rotation on [001]c) Carlsbad twins: rotation on [001] (typical simple twins in K-feldspar)(typical simple twins in K-feldspar)

d) Manebach twins: reflection on (001)d) Manebach twins: reflection on (001)e) Braveno twins: reflection on (021)e) Braveno twins: reflection on (021)

cross-hatched (tartan) twinning in microcline:cross-hatched (tartan) twinning in microcline:albite + periclinealbite + pericline

produced during inversion from orthoclaseproduced during inversion from orthoclase

a) b)a) b)

c)c)

e)e)

d)d)


plagioclase:plagioclase: “normal” zoning from Ca-rich cores to Na-rich rims “normal” zoning from Ca-rich cores to Na-rich rims reflects crystallisation from a fractionating magmareflects crystallisation from a fractionating magma

distinguishing featuresdistinguishing features (plag vs Kfd or qtz): (plag vs Kfd or qtz):polysynthetic (“barcode”) twinning; zoning common; exsolution rarepolysynthetic (“barcode”) twinning; zoning common; exsolution rarebiaxial +ve (Anbiaxial +ve (An0-200-20) or –ve (An) or –ve (An20-10020-100), 2V large), 2V large


alkali feldspar: alkali feldspar: exsolution lamellae (“perthite”)exsolution lamellae (“perthite”)form during form during unmixingunmixing of of homogeneous K,Na-feldspar homogeneous K,Na-feldspar during slow cooling during slow cooling (subsolidus solvus)(subsolidus solvus)

distinguishing features 1:distinguishing features 1: (Kfd vs plag or qtz):(Kfd vs plag or qtz):

simple (Carlsbad) or cross-simple (Carlsbad) or cross- hatched (tartan) twins; hatched (tartan) twins; exsolution common; exsolution common; zoning relatively rare; zoning relatively rare; biaxial –vebiaxial –ve

distinguishing featuresdistinguishing features 2:2:(sanidine vs orthoclase vs microcline)(sanidine vs orthoclase vs microcline)::

sanidine: small 2V, simple twinssanidine: small 2V, simple twinsorthoclase: large 2V, simple twinsorthoclase: large 2V, simple twinsmicrocline: large 2V, tartan twinsmicrocline: large 2V, tartan twins

anorthoclaseanorthoclase

occurrence: occurrence: most abundant mineral in Earth’s crustmost abundant mineral in Earth’s crust ((generally not stable in the mantle)generally not stable in the mantle)

plagplag – essential (dominant) mineral in mafic and intermediate igneous – essential (dominant) mineral in mafic and intermediate igneousrocks (basalts, andesites, etc.)rocks (basalts, andesites, etc.)

- important constituent of most felsic and alkaline igneous rocks- important constituent of most felsic and alkaline igneous rocks- present in metamorphic equivalents of these rocks, as well as- present in metamorphic equivalents of these rocks, as well as metasedimentary rocks (marbles, pelites)metasedimentary rocks (marbles, pelites)- common detrital mineral in sedimentary rockscommon detrital mineral in sedimentary rocks- present in many hydrothermal vein deposits- present in many hydrothermal vein deposits

alkali fdalkali fd – essential mineral in felsic and alkaline igneous rocks, – essential mineral in felsic and alkaline igneous rocks, common in some intermediate igneous rockscommon in some intermediate igneous rocks

- present in some high-grade metamorphic rocks (granitioid- present in some high-grade metamorphic rocks (granitioidand pelitic gneisses, migmatites)and pelitic gneisses, migmatites)

- common detrital mineral in sedimentary rocks (also authigenic)- common detrital mineral in sedimentary rocks (also authigenic)- present in many hydrothermal vein deposits (var. “adularia”)- present in many hydrothermal vein deposits (var. “adularia”)

use: use: semi-precious stone (moonstone, labradorite)semi-precious stone (moonstone, labradorite)aggregate, decorative stoneaggregate, decorative stonefiller, abrasive, whitener, ceramicsfiller, abrasive, whitener, ceramics


Charge BalanceCharge Balance

Since Na and Ca differ in valence, Al has to Since Na and Ca differ in valence, Al has to substitute for Si to compensatesubstitute for Si to compensate

The Al-Si orderings of albite and anorthite are The Al-Si orderings of albite and anorthite are different, and at low temperatures, plagioclases in different, and at low temperatures, plagioclases in the middle of the composition range also exsolve, the middle of the composition range also exsolve, but on a submicroscopic scalebut on a submicroscopic scale

These submicroscopic textures are probably These submicroscopic textures are probably responsible for the iridescence of some responsible for the iridescence of some plagioclasesplagioclases

FeldspathoidsFeldspathoids

Alumino – silicates but contain less SiOAlumino – silicates but contain less SiO22

than feldsparsthan feldspars They are rich in alkalisThey are rich in alkalis The feldspathorids often include unusual The feldspathorids often include unusual

anions such as Clanions such as Cl--, CO, CO33--, etc. , etc.

Important FeldspathoidsImportant Feldspathoids

ScapolitesScapolites

Metamorphic rock minerals probably Metamorphic rock minerals probably derived from feldsparsderived from feldspars

The alumino-silicate framework forms The alumino-silicate framework forms chains in the c-direction and has large open chains in the c-direction and has large open spaces which can accommodate large spaces which can accommodate large anions such a Cl, COanions such a Cl, CO33, SO, SO44

Scapolite MineralsScapolite Minerals

Marialite NaMarialite Na44(AlSi(AlSi33OO88))33(Cl(Cl22,CO,CO33,SO,SO44))

MeioniteMeionite Ca Ca44(Al(Al22SiSi22OO88))33(Cl(Cl22,CO,CO33,SO,SO44))

Marialite clusterMarialite cluster

ZeolitesZeolites Hydrous alumino-silicates Hydrous alumino-silicates

with very open structures.with very open structures. Rings of A1ORings of A1O44 and SiO and SiO44

tetrahedra are penetrated tetrahedra are penetrated by open channels in the by open channels in the structurestructure

Non-silicon cations hold Non-silicon cations hold the structure together.the structure together.

StilbiteStilbite

Cation ExchangeCation Exchange

Water can easily pass though these channels and Water can easily pass though these channels and dissolve and replace the cations present in the dissolve and replace the cations present in the structurestructure

This process in known as cation exchange and is This process in known as cation exchange and is reversiblereversible

Thus, the zeolites can serve as catalysts and water-Thus, the zeolites can serve as catalysts and water-softening agentssoftening agents

Petroleum companies have been particularly Petroleum companies have been particularly interested in zeolites for this reasoninterested in zeolites for this reason

Important Natural Zeolites Important Natural Zeolites

ChabaziteChabazite CaCa22(Al(Al22SiSi44OO1212)∙6H)∙6H22O O

HeulanditeHeulandite Ca(AlCa(Al22SiSi77001818)∙6H)∙6H22O O StilbiteStilbite

(Na,K,Ca(Na,K,Ca0.50.5))99Na(AlNa(Al99SiSi2727OO7272)∙28H)∙28H22O O

NatroliteNatrolite NaNa22(Al(Al22SiSi33OO1010)∙2H)∙2H22O O

AnalcimeAnalcime Na(AlSiNa(AlSi22OO66)∙H)∙H22O O

Fig. 2.9Fig. 2.9 From bottom to topFrom bottom to top

Increasing Increasing Fe/Mg/CaFe/Mg/Ca

Decreasing silicaDecreasing silica Increasing densityIncreasing density Darker minerals Darker minerals

DecreasingDecreasingSilicaSilica

29% 14%29% 14%

<20% 20%<20% 20%

<3% 23%<3% 23%

<2% 25% <2% 25%

(0) 33%(0) 33% (0) 23%(0) 23% (0) (0) 15%*15%*

% of Tot. # of atoms% of Tot. # of atoms Fe/Mg:Fe/Mg: Silicon:Silicon:

IncreasingIncreasingFe/Mg/CaFe/Mg/Ca QuartzQuartz

K and Na Feldspar K and Na Feldspar

Ca FeldsparCa Feldspar

Systematic SilicateSystematic SilicateMineralogyMineralogy

IncreasingIncreasingDensityDensity

OlivineOlivine

PyroxenePyroxeneGroupGroup

AmphiboleAmphiboleGroupGroup

MicaMicaGroupGroup

mineral-mineral silikat

Documents

hydrothermal

alkaline igneous

quartz liquidcristobalite

independent

independent

representing

layers forms

common detrital