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
KJM3100 V2008 Hardness Substance or Mineral Hardness scale (Mohs) 1 Liquid 2 Gypsum 1 Talc (Mg Si O (OH) ) 3 4 10 2 2.5 to 3 Gold, Silver 3 Calcite, Copper penny 2 Gypsum (CaSO4·2H2O) 4 Fluorite
3 Calcite (CaCO3) 4 to 4.5 Platinum 4 to 5 Iron 4 Fluorite (CaF2) 5 Apatite 6 Orthoclase 5 Apatite (Ca (PO ) (OH-,Cl-,F-)) 5 4 3 6.5 Iron pyrite 6 to 7 Glass, Vitreous pure silica 6 Orthoclase Feldspar (KAlSi3O8) 7 Quartz 7 Quartz (SiO2) 7 and up Hardened steel 8 Topaz - - 8 Topaz (Al2SiO4(OH ,F )2) 9 Corundum 9 Corundum (Al O ) 10 Garnet 2 3 11 Fused zirconia 10 Diamond (C) 12 Fused alumina 13 Silicon carbide 14 Boron carbide 15 Diamond KJM3100 V2008
KJM3100 V2008 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 CaTiO3 Spinel MgAl2O4 Rutile TiO2 Rock Salt NaCl, MgO
Corundum Al2O3
Garnet Olivine … …
KJM3100 V2008 SILICATE CLASSIFICATION Class Arrangement of Shared corners Repeat unit Si:O Example tetrahredra 4- Nesosilicates Independent 0SiO4 1:4 Olivine tetrahedra 6- Sorosilicates Pair of 1Si2O7 1:3.5 Hemimorphite tetrahedra sharing corner 2- Cyclosilicates Closed rings of 2SiO3 1:3 Tourmaline tetrahedra 2- Inosilicates Infinite single 2SiO3 1:3 Pyroxenes chain of tetrahedra 6- Infinite double 2.5 Si4O11 1:2.75 Amphiboles chains of tetrahedra 2- Phyllosilicates Infinite sheets 3Si2O5 1:2.5 Micas of tetrahedra
Tektosilicates Unbounded 4SiO2 1:2 Quartz, framework of feldspars tetrahedra KJM3100 V2008
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)2-3 (Mg, Fe, Al)5 [(Si,Al)8O22] (OH)2
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Mineral Structures Silicates are classified on the basis of Si-O polymerism 4- The building unit: [SiO4] tetrahedron
KJM3100 V2008 Mineral Structures Silicates are classified on the basis of Si-O polymerism
4- [SiO4] Independent tetrahedra Nesosilicates
Examples: olivine garnet
6- [Si2O7] Double tetrahedra Sorosilicates
Examples: lawsonite
2- n[SiO3] n = 3, 4, 6 Cyclosilicates
Examples: benitoite BaTi[Si3O9]
axinite Ca3Al2BO3[Si4O12]OH
beryl Be3Al2[Si6O18] (aquamarine, emerald) KJM3100 V2008
Mineral Structures Silicates are classified on the basis of Si-O polymerism
2- 4- [SiO3] single chains Inosilicates [Si4O11] Double tetrahedra pryoxenes pyroxenoids amphiboles
KJM3100 V2008 Mineral Structures Silicates are classified on the basis of Si-O polymerism
2- [Si2O5] Sheets of tetrahedra Phyllosilicates micas talc clay minerals serpentine
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Mineral Structures Silicates are classified on the basis of Si-O polymerism
low-quartz
[SiO2] 3-D frameworks of tetrahedra: fully polymerized Tectosilicates quartz and the silica minerals feldspars feldspathoids zeolites
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Mineral Structures
Nesosilicates: independent SiO4 tetrahedra
KJM3100 V2008 Olivine group
Examples:
Forsterite Mg2SiO4 Fayalite Fe(II)2SiO4 Tephroite Mn(II)2SiO4 Liebenbergite (Ni,Mg)2SiO4 Monticellite CaMgSiO4 Kirschsteinite CaFe(II)SiO4 Glaucochroite CaMnSiO4 KJM3100 V2008
Nesosilicates: independent SiO4 tetrahedra
b
c
projection
Olivine (100) view blue = M1 yellow = M2 KJM3100 V2008 Nesosilicates: independent SiO4 tetrahedra
b
c
perspective
Olivine (100) view blue = M1 yellow = M2 KJM3100 V2008
Nesosilicates: independent SiO4 tetrahedra
b
M1 in rows and share edges
M2 form layers in a-c that share a corners
Some M2 and M1 share edges
Olivine (001) view blue = M1 yellow = M2 KJM3100 V2008 Nesosilicates: independent SiO4 tetrahedra
b
c
M1 and M2 as polyhedra
Olivine (100) view blue = M1 yellow = M2 KJM3100 V2008
Green sand beach, Papakolea, Hawaii
KJM3100 V2008 Nesosilicates: independent SiO4 tetrahedra 2+ 3+ Garnet: A 3 B 2 [SiO4]3 “Pyralspites” - B = Al
Pyrope: Mg3 Al2 [SiO4]3 Almandine: Fe3 Al2 [SiO4]3 Spessartine: Mn3 Al2 [SiO4]3 “Ugrandites” - A = Ca
Uvarovite: Ca3 Cr2 [SiO4]3 Grossularite: Ca3 Al2 [SiO4]3 Andradite: Ca3 Fe2 [SiO4]3
Garnet (001) view blue = Si purple = B turquoise = A KJM3100 V2008
Nesosilicates: independent SiO4 tetrahedra 2+ 3+ Garnet: A 3 B 2 [SiO4]3 “Pyralspites” - B = Al
Pyrope: Mg3 Al2 [SiO4]3 a 2 Almandine: Fe3 Al2 [SiO4]3 a1 Spessartine: Mn3 Al2 [SiO4]3 “Ugrandites” - A = Ca
Uvarovite: Ca3 Cr2 [SiO4]3 a3 Grossularite: Ca3 Al2 [SiO4]3 Andradite: Ca3 Fe2 [SiO4]3
Garnet (111) view blue = Si purple = B turquoise = A KJM3100 V2008 YIG-YAG
Y3Fe5O12 , Y3Al5O12
Garnet: A(II)3B(III)2 [SiO4]3
YIG: Y3Fe(III)2 [Fe(III)O4]3 YAG: Y3Al2 [AlO4]3
YIG: Magnetic domains
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.
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Inosilicates: single chains- pyroxenes
b Diopside: CaMg [Si2O6]
Where are the Si-O-Si-O chains??
β β a sin a sin
Ruby w. diopside
Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) KJM3100 V2008 Inosilicates: single chains- pyroxenes
b
β β a sin a sin
Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) KJM3100 V2008
Inosilicates: single chains- pyroxenes
b
β β a sin a sin
Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) KJM3100 V2008 Inosilicates: single chains- pyroxenes
b
β β a sin a sin
Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) KJM3100 V2008
Inosilicates: single chains- pyroxenes
b
β β a sin a sin
Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) KJM3100 V2008 Inosilicates: single chains- pyroxenes
b
β β a sin a sin
Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) KJM3100 V2008
Inosilicates: single chains- pyroxenes
Perspective view
Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) KJM3100 V2008 Inosilicates: single chains- pyroxenes
IV slab
VI slab
IV slab
β β a sin a sin VI slab
IV slab
VI slab
IV slab
b Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) KJM3100 V2008
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 KJM3100 V2008 Pyroxenoids “Ideal” pyroxene chains with 5.2 A repeat (2 tetrahedra) become distorted as other cations occupy VI sites
17.4 A
12.5 A 7.1 A 5.2 A
Pyroxene Wollastonite Rhodonite Pyroxmangite
2-tet repeat (Ca → M1) MnSiO3 (Mn, Fe)SiO3 KJM3100 V2008 → 3-tet repeat → 5-tet repeat → 7-tet repeat
Inosilicates: double chains- amphiboles
b
Hornblende:
(Ca, Na)2-3 (Mg, Fe, Al)5 [(Si,Al)8O22] (OH)2
β β a sin a sin
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) little turquoise ball = H KJM3100 V2008 Phyllosilicates
SiO4 tetrahedra polymerized into 2-D sheets: [Si2O5] Apical O’s are unpolymerized and are bonded to other constituents
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Phyllosilicates
Tetrahedral layers are bonded to octahedral layers (OH) pairs are located in center of T rings where no apical O
KJM3100 V2008 Phyllosilicates
Octahedral layers can be understood by analogy with hydroxides
Brucite: Mg(OH)2
Layers of octahedral Mg in coordination with (OH)
Large spacing along c due c to weak van der Waals bonds
KJM3100 V2008 Hydrotalcite
Phyllosilicates
a2
a1
Gibbsite: Al(OH)3 Layers of octahedral Al in coordination with (OH) Al3+ means that only 2/3 of the VI sites may be occupied for charge-balance reasons Brucite-type layers may be called trioctahedral and gibbsite-type dioctahedral KJM3100 V2008 Phyllosilicates
T Yellow = (OH) O - vdw T Kaolinite: Al2 [Si2O5] (OH)4 O T-layers and diocathedral (Al3+) layers T-layers and diocathedral (Al ) layers - vdw (OH) at center of T-rings and fill base of VI layer → T
KJM3100 V2008 weak van der Waals bonds between T-O groups O
Phyllosilicates
T Yellow = (OH) O - vdw T Serpentine: Mg3 [Si2O5] (OH)4 O T-layers and triocathedral (Mg2+) layers T-layers and triocathedral (Mg ) layers - vdw (OH) at center of T-rings and fill base of VI layer → T
KJM3100 V2008 weak van der Waals bonds between T-O groups O Serpentine
Antigorite maintains a sheet-like form by alternating segments of opposite curvature
Chrysotile does not do this and tends to roll into tubes
Octahedra are a bit larger than tetrahedral match, so they cause bending of the T-O layers (after Klein and Hurlbut, 1999). KJM3100 V2008
Chrysotile, asbestos
KJM3100 V2008 Serpentine Veblen and Busek, 1979, Science 206, 1398-1400.
S = serpentine T = talc Nagby and Faust (1956) Am. Mineralogist 41, 817-836.
The rolled tubes in chrysotile resolves the apparent paradox of asbestosform sheet silicates KJM3100 V2008
Phyllosilicates
T O T - vdw T O Yellow = (OH) T
Pyrophyllite: Al2 [Si4O10] (OH)2 - vdw T T-layer - diocathedral (Al3+) layer - T-layer T O weak van der Waals bonds between T - O - T groups T KJM3100 V2008 Phyllosilicates
T O T - vdw Yellow = (OH) T O T
Talc: Mg3 [Si4O10] (OH)2 - vdw T T-layer - triocathedral (Mg2+) layer - T-layer T O weak van der Waals bonds between T - O - T groups T KJM3100 V2008
Phyllosilicates
T O T K T O T K T Muscovite: K Al [Si AlO ] (OH) (coupled K - AlIV) 2 3 10 2 O T-layer - diocathedral (Al3+) layer - T-layer - K T KJM3100 V2008 K between T - O - T groups is stronger than vdw Phyllosilicates
T O T K T O T K T Phlogopite: K Mg [Si AlO ] (OH) 3 3 10 2 O T-layer - triocathedral (Mg2+) layer - T-layer - K T KJM3100 V2008 K between T - O - T groups is stronger than vdw
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.
KJM3100 V2008 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 OF GOLDSCHMIDT’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.
KJM3100 V2008 COUPLED SUBSTITUTIONS
4+ 3+ Can Th substitute for Ce in monazite (CePO4)?
Rule 1: When CN = 9, rTh4+ = 1.17 Å, rCe3+ = 1.23Å. OK Rule 2: Only 1 charge unit difference. OK Rule 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. Hmm Rule 2: Only 1 charge unit difference. OK Rule 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
Small amounts of Si will be present in monazite.
Composition: (Ce, La, Pr, Nd, Th, Y)PO4
KJM3100 V2008 Roald Hoffmann: An Unusual State of Matter, in "Bound" ed. W. Carleton, C. Bond, Cornell Univ. (1986)
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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+
KJM3100 V2008 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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