lect 4 mineral visual

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Lecture z x y Soil Mineralogy and Chemistry Phyllosilicate Minerals Phyllosilicates, NO layer charge T:O trioctahedral dioctahedral oct oct (class) octahedra gibbsite brucite 1:1 tet oct tet oct kaolinite serpentine 2:1 tet oct tet oct tet tet talc pyrophyllite Building of Tetrahedral Sheets * Linked SiO4 tetrahedra SiO4 Tetrahedron z z x y x y z y z x y x z y x z Si6O18 z y x Linking Rings to Form Tetrahedral Sheets Tetrahedral Sheet x y z Si:O 2:5 Terminal Bonds terminal bonds z x y Terminal Bonds: Ionizable Functional Groups O Al Al-OH2+  Al-OHo + H+  Al-O- + H+ Low pH High pH -pH-dependent charge - edges of phyllosilicates; all surface on Fe- and Al-oxides Phyllosilicates: 2:1 with layer charge K+ micas 2:1 clay minerals tet oct tet oct tet tet K+ K+ tet oct tet unit of (-) layer charge per formula unit 2+ H2O H2O H2O Ca K+ tet oct tet < unit of (-) layer charge per formula unit General Classes (layer build-up) of Phyllosilicate Minerals: Layer Type Charge† Trioctahedral Dioctahedral octahedra brucite, Mg(OH)2 gibbsite, Al(OH)3 tet : oct serpentine, Mg3Si2O5(OH)4 kaolinite, Al2Si2O5(OH)4 tet : oct talc, Mg3Si4O10(OH)2 tet: oct phlogopite KMg3(AlSi3O10)(OH)2 biotite KFe3(AlSi3O10)(OH)2 0.6-0.8 illite (hydrous mica) K(Na,Ca) Al1.3Fe0.4Mn0.2Si3.4Al0.6O10(OH)2 pyrophyllite, Al2Si4O10(OH)2 muscovite KAl2(AlSi3O10)(OH)2 0.6-0.9 vermiculite 0.25-0.6 smectite † The layer charge per formula unit Swelling Potential? Interlayer Status: d-spacing Structure d-spacing K+ (and mica) Properties of Clay Minerals Kaolinite Smectite Vermiculite Illite Humus Size (µm) 0.1-5.0 Oxisol) Mol E/I E/I Alf Ult Organic Matter - reactive functional groups: carboxyl, hydroxyl, phenolic * Humus, Humic Acid, Fulvic Acid Flocculation and Aggregation + Flocculation (chemical) Aggregation (organic gluing) Organic Matter Promoted Aggregation [...]... (m2/g) External Internal 10-50 70-150 500-700 50-100 45 0-600 50-100 5-100 - Interlayer Spacing (nm) 0.7 1.0-2.0 1.0-1 .4 1.0 - Cation CEC cmol/Kg Sorption 5-15 85-110 100-120 15 -40 100-300 Accessory Minerals Kaolin and Oxide Rich Soil Western GA Ultisol Smectite Soil Iron and Al-oxide Rich ? NE Montana Vertisol Hawaiian Oxisol Clay mineralogy reflects weathering processes Micas  Vermiculite  Smectite... Mg3Si4O10(OH)2 2 tet: 1 oct 1 phlogopite KMg3(AlSi3O10)(OH)2 1 biotite KFe3(AlSi3O10)(OH)2 0.6-0.8 illite (hydrous mica) K(Na,Ca) Al1.3Fe0.4Mn0.2Si3.4Al0.6O10(OH)2 pyrophyllite, Al2Si4O10(OH)2 muscovite KAl2(AlSi3O10)(OH)2 0.6-0.9 vermiculite 0.25-0.6 smectite † The layer charge per formula unit Swelling Potential? Interlayer Status: d-spacing Structure d-spacing K+ (and mica) Properties of Clay Minerals... clay minerals tet oct tet oct tet tet K+ K+ tet oct tet 1 unit of (-) layer charge per formula unit 2+ H2O H2O H2O Ca K+ tet oct tet < 1 unit of (-) layer charge per formula unit General Classes (layer build-up) of Phyllosilicate Minerals: Layer Type Charge† Trioctahedral Dioctahedral 1 octahedra 0 brucite, Mg(OH)2 gibbsite, Al(OH)3 1 tet : 1 oct 0 serpentine, Mg3Si2O5(OH )4 kaolinite, Al2Si2O5(OH )4 2... Octahedral-Tetrahedral Linkage Sharing of Apical Oxygens in Tetrahdral Sheet with Hydroxyls of Octahedral Sheet Serpentine (1:1 trioctahedral mineral) tet oct z x y Sharing of Apical Oxygens in Tetrahdral Sheet with Hydroxyls of Two Octahedral Sheets Talc (2:1 trioctahedral mineral) tet oct tet z x y Short-hand Symbols tet oct z x y Short hand, Block notation Phyllosilicates, NO layer charge T:O trioctahedral... gibbsite brucite 1:1 tet oct tet oct kaolinite serpentine 2:1 tet oct tet oct tet tet pyrophyllite talc Charge Development Isomorphic Substitution  permanent (layer) charge Isomorphic Substitution tet Si4+ oct Mg2+ z x y Al3+ Al3+, Fe3+ NET Charge - - - - - - - ++ - ++ - ++ - ++ - ++ - ++ - ++ - 0 Isomorphic substitution - - - - - - - ++ - + - ++ - ++ - ++ - + - ++ - -2 Charge Development Terminal Bonds
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