minerals; the background of materials science - · pdf fileminerals; the background of...

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KJM3100 V2006

Minerals; The background of materials science

Formation, structure, properties and applications of minerals are in many ways the starting points of materials science.

Learning from Nature (stealing “ideas” matured over millions of years) is a good way to make some progress.

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Minerals

•naturally occurring

•inorganic

•solid

•fixed composition or within fixed range

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Hardness scale (Mohs)

1 Talc (Mg3Si4O10(OH)2)

2 Gypsum (CaSO4·2H2O)

3 Calcite (CaCO3)

4 Fluorite (CaF2)

5 Apatite (Ca5(PO4)3(OH-,Cl-,F-))

6 Orthoclase Feldspar (KAlSi3O8)

7 Quartz (SiO2)

8 Topaz (Al2SiO4(OH-,F-)2)

9 Corundum (Al2O3)

10 Diamond (C) 1500

Hardness Substance or Mineral1 Liquid2 Gypsum2.5 to 3 Gold, Silver3 Calcite, Copper penny4 Fluorite4 to 4.5 Platinum4 to 5 Iron5 Apatite6 Orthoclase6.5 Iron pyrite6 to 7 Glass, Vitreous pure silica7 Quartz7 and up Hardened steel8 Topaz9 Corundum10 Garnet 11 Fused zirconia12 Fused alumina 13 Silicon carbide 14 Boron carbide 15 Diamond

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Formation of minerals

•Formation from melts•Solid state reactions•Hydrothermal conditions•Sedimentation/precipitation•Vapor phase deposition•Exsolution

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A few important mineral types/structures

Perovskite CaTiO3Spinel MgAl2O4Rutile TiO2Rock Salt NaCl, MgOCorundum Al2O3

GarnetOlivine……

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Class Arrangement oftetrahredra

Shared corners Repeat unit Si:O Example

Nesosilicates Independenttetrahedra

0 SiO44- 1:4 Olivine

Sorosilicates Pair oftetrahedrasharing corner

1 Si2O76- 1:3.5 Hemimorphite

Cyclosilicates Closed rings oftetrahedra

2 SiO32- 1:3 Tourmaline

Inosilicates Infinite singlechain oftetrahedra

2 SiO32- 1:3 Pyroxenes

Infinite doublechains oftetrahedra

2.5 Si4O116- 1:2.75 Amphiboles

Phyllosilicates Infinite sheetsof tetrahedra

3 Si2O52- 1:2.5 Micas

Tektosilicates Unboundedframework oftetrahedra

4 SiO2 1:2 Quartz,feldspars

SILICATE CLASSIFICATION

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Isomorphous replacement in silicates

Some cations and anions are readily replacable:(Not always carrying the same charge!)

Na+, Mg2+, Ca2+, Mn2+, Fe3+

O2-, F-, OH-

And typically:

Si4+, Al3+

E.g. 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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Mineral Structures

Silicates are classified on the basis of Si-O polymerismThe building unit: [SiO4]4- tetrahedron

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Mineral Structures

Silicates are classified on the basis of Si-O polymerism[SiO4]4- Independent tetrahedra Nesosilicates

Examples: olivine garnet

[Si2O7]6- Double tetrahedra Sorosilicates

Examples: lawsonite

n[SiO3]2- n = 3, 4, 6 Cyclosilicates

Examples: benitoite BaTi[Si3O9]axinite Ca3Al2BO3[Si4O12]OHberyl Be3Al2[Si6O18] (aquamarine, emerald)

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Mineral Structures

Silicates are classified on the basis of Si-O polymerism

[SiO3]2- single chains Inosilicates [Si4O11]4- Double tetrahedrapryoxenes pyroxenoids amphiboles

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Mineral Structures


[Si2O5]2- Sheets of tetrahedra Phyllosilicatesmicas talc clay minerals serpentine

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Mineral Structures


[SiO2] 3-D frameworks of tetrahedra: fully polymerized Tectosilicatesquartz and the silica minerals feldspars feldspathoids zeolites

lowlow--quartzquartz

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Mineral Structures

Nesosilicates: independent SiO4 tetrahedra

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Examples:

Forsterite Mg2SiO4Fayalite Fe(II)2SiO4Tephroite Mn(II)2SiO4 Liebenbergite (Ni,Mg)2SiO4Monticellite CaMgSiO4Kirschsteinite CaFe(II)SiO4Glaucochroite CaMnSiO4

Olivine group

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

bb

cc

projectionprojection

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KJM3100 V2006Olivine (100) view blue = M1 yellow = M2Olivine (100) view blue = M1 yellow = M2

bb

cc

perspectiveperspective


KJM3100 V2006Olivine (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


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

bb

cc

M1 and M2 as polyhedraM1 and M2 as polyhedra

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Green sand beach, Papakolea, Hawaii

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Garnet (001) view blue = Si purple = B turquoise = AGarnet (001) view blue = Si purple = B turquoise = A

Garnet: AGarnet: A2+2+33 BB3+3+

22 [SiO[SiO44]]3 3

““PyralspitesPyralspites”” -- B = AlB = AlPyPyrope: Mgrope: Mg33 AlAl22 [SiO[SiO44]]3 3 AlAlmandine: Femandine: Fe33 AlAl22 [SiO[SiO44]]33SpSpessartine: Mnessartine: Mn33 AlAl22 [SiO[SiO44]]33

““UgranditesUgrandites”” -- A = CaA = CaUUvarovitevarovite: Ca: Ca33 CrCr22 [SiO[SiO44]]33GrGrossularite: ossularite: CaCa33 AlAl22 [SiO[SiO44]]33AndAndradite: Caradite: Ca33 FeFe22 [SiO[SiO44]]33

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Garnet (111) view blue = Si purple = B turquoise = AGarnet (111) view blue = Si purple = B turquoise = A

Garnet: AGarnet: A2+2+33 BB3+3+

22 [SiO[SiO44]]3 3

““PyralspitesPyralspites”” -- B = AlB = AlPyPyrope: Mgrope: Mg33 AlAl22 [SiO[SiO44]]3 3 AlAlmandine: Femandine: Fe33 AlAl22 [SiO[SiO44]]33SpSpessartine: Mnessartine: Mn33 AlAl22 [SiO[SiO44]]33

““UgranditesUgrandites”” -- A = CaA = CaUUvarovitevarovite: Ca: Ca33 CrCr22 [SiO[SiO44]]33GrGrossularite: ossularite: CaCa33 AlAl22 [SiO[SiO44]]33AndAndradite: Caradite: Ca33 FeFe22 [SiO[SiO44]]33

aa11

aa22

aa33

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LED White light is currently achieved by using two different methods. One is by combining a blue 450nm – 470nm GaN (gallium nitride) LED with YAG (Yttrium Aluminum Garnet) phosphor. The blue wavelength excites the phosphor causing it to glow white.

YIG-YAGY3Fe5O12 , Y3Al5O12

YIG: Magnetic domains

Garnet: A(II)Garnet: A(II)33B(III)B(III)22 [SiO[SiO44]]33

YIG: YYIG: Y33Fe(III)Fe(III)22 [Fe(III)O[Fe(III)O44]]33YAG: YYAG: Y33AlAl22 [AlO[AlO44]]33

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Inosilicates: single chains- pyroxenes

Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)(Ca)

Diopside: Diopside: CaMgCaMg [Si[Si22OO66]]bb

a si

na

sin ββ

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

Ruby w. diopside

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bb

a si

na

sin ββ

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bb

a si

na

sin ββ

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bb

a si

na

sin ββ

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bb

a si

na

sin ββ

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bb

a si

na

sin ββ

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Perspective viewPerspective view

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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 ββ

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Pyroxene Chemistry

The general pyroxene formula: W1-P (X,Y)1+P Z2O6

Where– W = Ca Na– X = Mg Fe2+ Mn Ni Li– Y = Al Fe3+ Cr Ti– Z = Si Al

Anhydrous so high-temperature or dry conditions favor pyroxenes over amphiboles

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Pyroxenoids“Ideal” pyroxene chains with

5.2 A repeat (2 tetrahedra) become distorted as other cations occupy VI sites

WollastoniteWollastonite(Ca (Ca →→ M1) M1)

→→ 33--tet repeattet repeat

RhodoniteRhodoniteMnSiOMnSiO33

→→ 55--tet repeattet repeat

PyroxmangitePyroxmangite(Mn, Fe)SiO(Mn, Fe)SiO33→→ 77--tet repeattet repeat

PyroxenePyroxene22--tet repeattet repeat

7.1 A12.5 A

17.4 A

5.2 A

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Inosilicates: double chains- amphiboles

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

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

bb

a si

na

sin ββ

Hornblende (001) view dark blue = Si, Al purple = M1 rose = Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 M2 light blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purpllight blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purple ball = A (Na)e ball = A (Na)

little turquoise ball = Hlittle turquoise ball = H

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SiO4 tetrahedra polymerized into 2-D sheets: [Si2O5]Apical O’s are unpolymerized and are bonded to other constituents

Phyllosilicates

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Tetrahedral layers are bonded to octahedral layers (OH) pairs are located in center of T rings where no apical O

Phyllosilicates

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Octahedral layers can be understood by analogy with hydroxides

Phyllosilicates

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 to weak van derder WaalsWaalsbondsbonds

cc

Hydrotalcite

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Phyllosilicates

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

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Phyllosilicates

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

TT--layers and layers and didiocathedralocathedral (Al(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 weak van derder WaalsWaals bonds between Tbonds between T--O groups O groups

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Phyllosilicates

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

TT--layers and layers and tritriocathedralocathedral (Mg(Mg2+2+) 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 weak van derder WaalsWaals bonds between Tbonds between T--O groups O groups

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Serpentine

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 layers (after Klein and HurlbutHurlbut, 1999)., 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

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ChrysotileChrysotile, asbestos, asbestos

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Serpentine

The rolled tubes in chrysotile resolves the apparent The rolled tubes in chrysotile resolves the apparent paradox of paradox of asbestosformasbestosform sheet silicatessheet silicates

S = serpentine T = talcS = serpentine T = talcNagby and Faust (1956) Am. Mineralogist 41, 817-836.

Veblen and Busek, 1979, Science 206, 1398-1400.

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Phyllosilicates

Pyrophyllite:Pyrophyllite: AlAl22 [Si[Si44OO1010] (OH)] (OH)22

TT--layer layer -- didiocathedralocathedral (Al(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 weak van derder WaalsWaals bonds between T bonds between T -- O O -- T groups T groups

Yellow = (OH)Yellow = (OH)

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Phyllosilicates

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

TT--layer layer -- tritriocathedralocathedral (Mg(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 weak van derder WaalsWaals bonds between T bonds between T -- O O -- T groups T groups

Yellow = (OH)Yellow = (OH)

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Phyllosilicates

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

TT--layer layer -- didiocathedralocathedral (Al(Al3+3+) layer ) layer -- TT--layer layer -- KK

T T O O T T KKT T O O T T KKT T O O TT

K between T K between T -- O O -- T groups is stronger than T groups is stronger than vdwvdw

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Phyllosilicates

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

TT--layer layer -- tritriocathedralocathedral (Mg(Mg2+2+) layer ) layer -- TT--layer layer -- KK

T T O O T T KKT T O O T T KKT T O O TT

K between T K between T -- O O -- T groups is stronger than T groups is stronger than vdwvdw

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SOLID SOLUTION

• Occurs when, in a crystalline solid, one element substitutes for another.

• For example, a garnet may have the composition: (Mg1.7Fe0.9Mn0.2Ca0.2)Al2Si3O12.

• The garnet is a solid solution of the following end member components:

Pyrope - Mg3Al2Si3O12; Spessartine - Mn3Al2Si3O12;Almandine - Fe3Al2Si3O12; and Grossular -

Ca3Al2Si3O12.

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GOLDSCHMIDT’S RULES

1. The ions of one element can extensively replace those of another in ionic crystals if their radii differ by less than approximately 15%.

2. Ions whose charges differ by one unit substitute readily for one another provided electrical neutrality of the crystal is maintained. If the charges differ by more than one unit, substitution is generally slight.

3. When two different ions can occupy a particular position in a crystal lattice, the ion with the higher ionic potential forms a stronger bond with the anions surrounding the site.

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RINGWOOD’S MODIFICATION OFGOLDSCHMIDT’S RULES

4. Substitutions may be limited, even when the size and charge criteria are satisfied, when the competing ions have different electronegativities and form bonds of different ionic character.

This rule was proposed in 1955 to explain discrepancies with respect to the first three Goldschmidt rules.

For example, Na+ and Cu+ have the same radius and charge, but do not substitute for one another.

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COUPLED SUBSTITUTIONS

Can Th4+ substitute for Ce3+ in monazite (CePO4)? Rule 1: When CN = 9, rTh4+ = 1.17 Å, rCe3+ = 1.23Å. OKRule 2: Only 1 charge unit difference. OKRule 3: Ionic potential (Th4+) = 4/1.17 = 3.42; ionic

potential (Ce3+) = 3/1.23 = 2.44, so Th4+ is preferred!Rule 4: χTh = 1.3; χCe = 1.1. OK

But we must have a coupled substitution to maintain neutrality:

Th4+ + Si4+ ↔ Ce3+ + P5+

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But can Si4+ substitute for P5+ according to Goldschmidt’s rules?

Rule 1: When CN = 4, rSi4+ = 0.34 Å, rP5+ = 0.25 Å. OK

Rule 2: Only 1 charge unit difference. OKRule 3: Ionic potential (Si4+) = 4/0.34 = 11.76; ionic

potential (P5+) = 5/0.25 = 20, so P5+ is preferred.Rule 4: χSi = 1.8; χP = 2.1. OK

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OTHER EXAMPLES OF COUPLED SUBSTITUTION

Plagioclase: NaAlSi3O8 - CaAl2Si2O8

Na+ + Si4+ ↔ Ca2+ + Al3+

Gold and arsenic in pyrite (FeS2):Au+ + As3+ ↔ 2Fe2+

REE and Na in apatite (Ca5(PO4)3F):REE3+ + Na+ ↔ 2Ca2+

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INCOMPATIBLE VS. COMPATIBLE TRACE ELEMENTS

Incompatible elements: Elements that are too large and/or too highly charged to fit easily into common rock-forming minerals that crystallize from melts. These elements become concentrated in melts.

Large-ion lithophile elements (LIL’s): Incompatible owing to large size, e.g., Rb+, Cs+, Sr2+, Ba2+, (K+).

High-field strength elements (HFSE’s): Incompatible owing to high charge, e.g., Zr4+, Hf 4+, Ta4+, Nb5+, Th4+, U4+, Mo6+, W6+, etc.

Compatible elements: Elements that fit easily into rock-forming minerals, and may in fact be preferred, e.g., Cr, V, Ni, Co, Ti, etc.

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