Minerals; The background of materials science

Transcription

1 Minerals; he 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. Minerals naturally occurring inorganic solid fixed composition or within fixed range

2 Hardness scale (Mohs) 1 alc (Mg 3 Si 4 10 (H) 2 ) 2 Gypsum (CaS 4 2H 2 ) 3 Calcite (CaC 3 ) 4 Fluorite (CaF 2 ) 5 Apatite (Ca 5 (P 4 ) 3 (H -,Cl -,F - )) 6 rthoclase Feldspar (KAlSi 3 8 ) 7 Quartz (Si 2 ) 8 opaz (Al 2 Si 4 (H -,F - ) 2 ) 9 Corundum (Al 2 3 ) 10 Diamond (C) 1500 Hardness Substance or Mineral 1 Liquid 2 Gypsum 2.5 to 3 Gold, Silver 3 Calcite, Copper penny 4 Fluorite 4 to 4.5 Platinum 4 to 5 Iron 5 Apatite 6 rthoclase 6.5 Iron pyrite 6 to 7 Glass, Vitreous pure silica 7 Quartz 7 and up Hardened steel 8 opaz 9 Corundum 10 Garnet 11 Fused zirconia 12 Fused alumina 13 Silicon carbide 14 Boron carbide 15 Diamond

3 Formation of minerals Formation from melts Solid state reactions Hydrothermal conditions Sedimentation/precipitation Vapor phase deposition Exsolution A few important mineral types/structures Perovskite Cai 3 Spinel MgAl 2 4 Rutile i 2 Rock Salt NaCl, Mg Corundum Al 2 3 Garnet livine

4 Class Nesosilicates Sorosilicates Cyclosilicates Inosilicates Phyllosilicates ektosilicates SILICAE CLASSIFICAIN Arrangement of tetrahredra Independent tetrahedra Pair of tetrahedra sharing corner Closed rings of tetrahedra Infinite single chain of tetrahedra Infinite double chains of tetrahedra Infinite sheets of tetrahedra Unbounded framework of tetrahedra Shared corners Repeat unit Si: Example 0 Si Si Si Si Si Si :4 livine 1:3.5 Hemimorphite 1:3 ourmaline 1:3 Pyroxenes 1:2.75 Amphiboles 1:2.5 Micas 4 Si 2 1:2 Quartz, feldspars Isomorphous replacement in silicates Some cations and anions are readily replacable: (Not always carrying the same charge!) Na +, Mg 2+, Ca 2+, Mn 2+, Fe 3+ 2-, F -, H - And typically: Si 4+, Al 3+ E.g. Hornblende, (Ca, Na) 2-3 (Mg, Fe, Al) 5 [(Si,Al) 8 22 ] (H) 2

5 Mineral Structures Silicates are classified on the basis of Si- polymerism he building unit: [Si 4 ] 4- tetrahedron

6 Mineral Structures Silicates are classified on the basis of Si- polymerism [Si 4 ] 4- Independent tetrahedra Nesosilicates Examples: olivine garnet [Si 2 7 ] 6- Double tetrahedra Sorosilicates Examples: lawsonite n[si 3 ] 2- n = 3, 4, 6 Cyclosilicates Examples: benitoite Bai[Si 3 9 ] axinite Ca 3 Al 2 B 3 [Si 4 12 ]H beryl Be 3 Al 2 [Si 6 18 ] (aquamarine, emerald) Mineral Structures Silicates are classified on the basis of Si- polymerism [Si 3 ] 2- single chains Inosilicates [Si 4 11 ] 4- Double tetrahedra pryoxenes pyroxenoids amphiboles

7 Mineral Structures Silicates are classified on the basis of Si- polymerism [Si 2 5 ] 2- Sheets of tetrahedra Phyllosilicates micas talc clay minerals serpentine Mineral Structures Silicates are classified on the basis of Si- polymerism low-quartz [Si 2 ] 3-D frameworks of tetrahedra: fully polymerized ectosilicates quartz and the silica minerals feldspars feldspathoids zeolites

8 Mineral Structures Nesosilicates: independent Si 4 tetrahedra

9 livine group Examples: Forsterite Mg 2 Si 4 Fayalite Fe(II) 2 Si 4 ephroite Mn(II) 2 Si 4 Liebenbergite (Ni,Mg) 2 Si 4 Monticellite CaMgSi 4 Kirschsteinite CaFe(II)Si 4 Glaucochroite CaMnSi 4 Nesosilicates: independent Si 4 tetrahedra b c projection livine (100) view blue = M1 yellow = M2

10 Nesosilicates: independent Si 4 tetrahedra b c perspective livine (100) view blue = M1 yellow = M2 Nesosilicates: independent Si 4 tetrahedra b M1 in rows and share edges a M2 form layers in a-c a that share corners Some M2 and M1 share edges livine (001) view blue = M1 yellow = M2

11 Nesosilicates: independent Si 4 tetrahedra b c M1 and M2 as polyhedra livine (100) view blue = M1 yellow = M2 Green sand beach, Papakolea, Hawaii

12 Nesosilicates: independent Si 4 tetrahedra Garnet: A 2+ 3 B 3+ 2 [Si 4 ] 3 Pyralspites - B = Al Pyrope: Mg 3 Al 2 [Si 4 ] 3 Almandine: Fe 3 Al 2 [Si 4 ] 3 Spessartine: Mn 3 Al 2 [Si 4 ] 3 Ugrandites - A = Ca Uvarovite: : Ca 3 Cr 2 [Si 4 ] 3 Grossularite: Ca 3 Al 2 [Si 4 ] 3 Andradite: Ca 3 Fe 2 [Si 4 ] 3 Garnet (001) view blue = Si purple = B turquoise = A Nesosilicates: independent Si 4 tetrahedra Garnet: A 2+ 3 B 3+ 2 [Si 4 ] 3 a 1 a 3 a 2 Pyralspites - B = Al Pyrope: Mg 3 Al 2 [Si 4 ] 3 Almandine: Fe 3 Al 2 [Si 4 ] 3 Spessartine: Mn 3 Al 2 [Si 4 ] 3 Ugrandites - A = Ca Uvarovite: : Ca 3 Cr 2 [Si 4 ] 3 Grossularite: Ca 3 Al 2 [Si 4 ] 3 Andradite: Ca 3 Fe 2 [Si 4 ] 3 Garnet (111) view blue = Si purple = B turquoise = A

13 YIG-YAG Y 3 Fe 5 12, Y 3 Al 5 12 Garnet: A(II) 3 B(III) 2 [Si 4 ] 3 YIG: Y 3 Fe(III) 2 [Fe(III) 4 ] 3 YAG: Y 3 Al 2 [Al 4 ] 3 YIG: Magnetic domains LED White light is currently achieved by using two different methods. ne is by combining a blue 450nm 470nm GaN (gallium nitride) LED with YAG (Yttrium Aluminum Garnet) phosphor. he blue wavelength excites the phosphor causing it to glow white. Inosilicates: single chains- pyroxenes b Diopside: CaMg [Si 2 6 ] Where are the Si--Si Si- chains?? a sinβ Ruby w. diopside Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)

14 Inosilicates: single chains- pyroxenes b a sinβ Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) b Inosilicates: single chains- pyroxenes a sinβ Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)

15 Inosilicates: single chains- pyroxenes b a sinβ Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) b Inosilicates: single chains- pyroxenes a sinβ Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)

16 Inosilicates: single chains- pyroxenes b a sinβ Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) Inosilicates: single chains- pyroxenes Perspective view Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)

17 Inosilicates: single chains- pyroxenes IV slab VI slab IV slab a sinβ VI slab IV slab VI slab IV slab Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca) b Pyroxene Chemistry he general pyroxene formula: W 1-P (X,Y) 1+P Z 2 6 Where W = Ca Na X = Mg Fe 2+ Mn Ni Li Y = Al Fe 3+ Cr i Z = Si Al Anhydrous so high-temperature or dry conditions favor pyroxenes over amphiboles

18 Ideal pyroxene chains with 5.2 A repeat (2 tetrahedra) become distorted as other cations occupy VI sites Pyroxenoids 17.4 A 5.2 A 7.1 A 12.5 A Pyroxene 2-tet repeat Wollastonite (Ca M1) 3-tet repeat Rhodonite MnSi 3 5-tet repeat Pyroxmangite (Mn, Fe)Si 3 7-tet repeat Inosilicates: double chains- amphiboles b Hornblende: (Ca, Na) 2-3 (Mg, Fe, Al) 5 [(Si,Al) 8 22 ] (H) 2 a sinβ Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 light blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purple e ball = A (Na) little turquoise ball = H

19 Phyllosilicates Si 4 tetrahedra polymerized into 2-D sheets: [Si 2 5 ] Apical s are unpolymerized and are bonded to other constituents Phyllosilicates etrahedral layers are bonded to octahedral layers (H) pairs are located in center of rings where no apical

20 Phyllosilicates ctahedral layers can be understood by analogy with hydroxides Brucite: Mg(H) 2 Layers of octahedral Mg in coordination with (H) c Large spacing along c due to weak van der Waals bonds Hydrotalcite Phyllosilicates a 2 a 1 Gibbsite: Al(H) 3 Layers of octahedral Al in coordination with (H) Al 3+ means that only 2/3 of the VI sites may be occupied for charge-balance reasons Brucite-type type layers may be called trioctahedral and gibbsite-type type dioctahedral

21 Phyllosilicates Kaolinite: Al 2 [Si 2 5 ] (H) 4 -layers and diocathedral (Al 3+ ) layers Yellow = (H) (H) at center of -rings and fill base of VI layer weak van der Waals bonds between - groups - - vdw vdw Phyllosilicates Serpentine: Mg 3 [Si 2 5 ] (H) 4 -layers and triocathedral (Mg 2+ ) layers Yellow = (H) (H) at center of -rings and fill base of VI layer weak van der Waals bonds between - groups - - vdw vdw

22 Serpentine Antigorite maintains a sheet-like form by alternating segments of opposite curvature Chrysotile does not do this and tends to roll into tubes ctahedra are a bit larger than tetrahedral match, so they cause bending of the - layers (after Klein and Hurlbut,, 1999). Chrysotile,, asbestos

23 Serpentine Veblen and Busek, 1979, Science 206, Nagby and Faust (1956) Am. Mineralogist 41, S = serpentine = talc he rolled tubes in chrysotile resolves the apparent paradox of asbestosform sheet silicates Phyllosilicates Pyrophyllite: Al 2 [Si 4 10 ] (H) 2 Yellow = (H) -layer - diocathedral (Al 3+ ) layer - -layer weak van der Waals bonds between - - groups - - vdw vdw

24 Phyllosilicates alc: Mg 3 [Si 4 10 ] (H) 2 Yellow = (H) -layer - triocathedral (Mg 2+ ) layer - -layer weak van der Waals bonds between - - groups - - vdw vdw Phyllosilicates Muscovite: K Al 2 [Si 3 Al 10 ] (H) 2 (coupled K - Al -layer - diocathedral (Al 3+ ) layer - -layer - K K between - - groups is stronger than vdw Al IV IV ) K K

25 Phyllosilicates Phlogopite: K Mg 3 [Si 3 Al 10 ] (H) 2 -layer - triocathedral (Mg 2+ ) layer - -layer - K K between - - groups is stronger than vdw K K SLID SLUIN ccurs when, in a crystalline solid, one element substitutes for another. For example, a garnet may have the composition: (Mg 1.7 Fe 0.9 Mn 0.2 Ca 0.2 )Al 2 Si he garnet is a solid solution of the following end member components: Pyrope - Mg 3 Al 2 Si 3 12 ; Spessartine - Mn 3 Al 2 Si 3 12 ; Almandine - Fe 3 Al 2 Si 3 12 ; and Grossular - Ca 3 Al 2 Si 3 12.

26 GLDSCHMID S RULES 1. he 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. RINGWD S MDIFICAIN F GLDSCHMID 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. his 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.

27 CUPLED SUBSIUINS Can h 4+ substitute for Ce 3+ in monazite (CeP 4 )? Rule 1: When CN = 9, r h 4+ = 1.17 Å, r Ce 3+ = 1.23Å. K Rule 2: nly 1 charge unit difference. K Rule 3: Ionic potential (h 4+ ) = 4/1.17 = 3.42; ionic potential (Ce 3+ ) = 3/1.23 = 2.44, so h 4+ is preferred! Rule 4: χ h = 1.3; χ Ce = 1.1. K But we must have a coupled substitution to maintain neutrality: h 4+ + Si 4+ Ce 3+ + P 5+ But can Si 4+ substitute for P 5+ according to Goldschmidt s rules? Rule 1: When CN = 4, r Si 4+ = 0.34 Å, r P 5+ = 0.25 Å. K Rule 2: nly 1 charge unit difference. K Rule 3: Ionic potential (Si 4+ ) = 4/0.34 = 11.76; ionic potential (P 5+ ) = 5/0.25 = 20, so P 5+ is preferred. Rule 4: χ Si = 1.8; χ P = 2.1. K

28 HER EXAMPLES F CUPLED SUBSIUIN Plagioclase: NaAlSi 3 8 -CaAl 2 Si 2 8 Na + + Si 4+ Ca 2+ + Al 3+ Gold and arsenic in pyrite (FeS 2 ): Au + + As 3+ 2Fe 2+ REE and Na in apatite (Ca 5 (P 4 ) 3 F): REE 3+ + Na + 2Ca 2+ INCMPAIBLE VS. CMPAIBLE RACE ELEMENS Incompatible elements: Elements that are too large and/or too highly charged to fit easily into common rock-forming minerals that crystallize from melts. hese elements become concentrated in melts. Large-ion lithophile elements (LIL s): Incompatible owing to large size, e.g., Rb +, Cs +, Sr 2+, Ba 2+, (K + ). High-field strength elements (HFSE s): Incompatible owing to high charge, e.g., Zr 4+, Hf 4+, a 4+, Nb 5+, h 4+, U 4+, Mo 6+, W 6+, etc. Compatible elements: Elements that fit easily into rockforming minerals, and may in fact be preferred, e.g., Cr, V, Ni, Co, i, etc.