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Building Soil Minerals

Building Soil Minerals. EXPECTED ION CORRDINATION . BOND VALENCE . BOND VALENCE . Clay Minerals. BUILDING BLOCKS. Si 6 O 18. Tetrahedral Sheet. Side View (100) plane. Top View (001) plane. Structural Views: Anion Sheets. Creating Octahedral Sheets. - Filling of Anion Sheets.

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Building Soil Minerals

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  1. Building Soil Minerals

  2. EXPECTED ION CORRDINATION

  3. BOND VALENCE

  4. BOND VALENCE

  5. Clay Minerals

  6. BUILDING BLOCKS

  7. Si6O18

  8. Tetrahedral Sheet Side View (100) plane Top View (001) plane

  9. Structural Views: Anion Sheets

  10. Creating Octahedral Sheets - Filling of Anion Sheets Dioctahedral (trivalent ions) and Trioctahedral (divalent ions)

  11. (di)OCTAHEDRAL SITE FILLING Anion Sheet with Trivalent (Al3+) Cations

  12. (di)OCTAHEDRAL SITE FILLING Dioctahedral Sheet Without Basal Hydroxyls

  13. Octahedral Sheets Trioctahedral (divalent cation) View down [001] axis x y Dioctahedral (trivalent cation)

  14. Charge Development • Isomorphic substitution • Terminal (unsatisfied) bonds

  15. Charge Development • Isomorphic Substitution Tetrahedral Sites: Al3+ for Si4+g (-) charge Octahedral Sites: Mg2++ for Al3+g (-) charge Al3+ for Mg2+g (+) charge

  16. Charge Development • Terminal (unsatisfied) bonds surface surface - bond valence considerations

  17. Minerals within Soils

  18. Rock Ideal Weathering Series Entisol Inceptisol Mollisol Vertisol (clay mineralogy) Alfisol Ultisol Oxisol

  19. Rock Entisol Inceptisol Mollisol Alfisol Ultisol Oxisol

  20. Phyllosilicates:Clay Minerals Entisol Inceptisol Mollisol Alfisol Ultisol - Phyllosilicates dominate the clay size particles of most soils

  21. General Classes (layer build-up) of Phyllosilicate Minerals

  22. Oct. Octahedral Minerals Brucite, Mg(OH)2 Gibbsite, Al(OH)3

  23. 1:1 Phyllosilicates Sheets } tet 1:1 layer oct H-bonds H-bonds Kaolinite and Serpentine

  24. Kaolinite: Al2Si2O5(OH)4 - dioctahedral, 1:1 mineral

  25. Sharing of Apical Oxygens in Tetrahdral Sheet with Hydroxyls of Two Octahedral Sheets Talc (2:1 trioctahedral mineral) tet oct tet

  26. tet tet tet tet oct oct Micas Phlogopite: KMg3(AlSi3O10)(OH)2 Biotite: KFe3(AlSi3O10)(OH)2 Muscovite: KAl2(AlSi3O10)(OH)2 K+ K+ K+ Unit layer of charge

  27. K+

  28. Ditrigonal (hexagonal) Cavity Si6O18

  29. Ca2+ H2O K+ H2O H2O tet tet tet tet oct oct Expandable 2:1 Layer Phyllosilicates Illite (hydrous mica) Vermiculite Smectite Illite: KAl1.3Fe0.4Mg0.2Si3.4Al0.6O10(OH)2

  30. Ca2+ H2O K+ H2O H2O tet tet tet tet oct oct Expandable 2:1 Layer Phyllosilicates Vermiculite dioctahedral:Nax(Al,Fe)2(Si4-xAlx)O10(OH)2nH2O trioctahedral: Nax(Mg,Fe)3(Si4-xAlx)O10(OH)2nH2O

  31. Expandable 2:1 Layer Phyllosilicates Smectite Dioctahedral Forms: MontmorilloniteNax(Al 2-xMgx)Si4O10(OH)2 Beidellite:Nax(Al 2)(AlxSi4-x)O10(OH)2 Trioctahedral Forms: Saponite: Nax-y(Mg3-yAly)3(Si4-xAlx)O10(OH)2 Hectorite:Nax(Mg3-xLix)3Si4O10(OH)2

  32. Interlayer Expansion Two Dominant Factors: 1. Structural Charge 2. Interlayer Ion

  33. 2:1:1 Layer Phyllosilicates [Mg2Al1(OH )6]Mg3(Si3Al)O10(OH)2

  34. tet tet tet tet oct (b) oct oct 2:1:1 Layer Phyllosilicates Hydroxy Interlayer Vermiculite (HIV) Hydroxy Interlayer Smectite (HIS) - pedogenic chlorites versus true chlorites [Mg2Al1(OH )6]Mg3(Si3Al)O10(OH)2

  35. Accessory Minerals Iron Oxides Aluminum Oxides Manganese Oxides

  36. Accessory Minerals Andisol Hydrous Silicates and Aluminosilicates - volcanic ash

  37. 100 nm Accessory Minerals Hydrous Silicates and Aluminosilicates

  38. Identifying Soil Minerals X-ray Diffraction

  39. Useful (Common) Methods/Approaches Optical Microscopy Infrared Spectroscopy Thermal Analysis X-ray Diffraction (XRD) Physical Properties

  40. X-ray Diffraction Attributes Limitations

  41. X-ray Diffraction: Foundation Consider wave properties

  42. X-ray Diffraction: Foundation Constructive versus Destructive Interference

  43. X-ray Diffraction: Foundation Bragg’s Law: n l = 2d sin q • = wavelength (0.5 to 2.5 Å) d q

  44. General Classes (layer build-up) of Phyllosilicate Minerals

  45. Octahedral Layer Only: Brucite, Mg(OH)2 Oct. z y 1:1 Mineral: Serpentine, Mg3Si2O5(OH)4 Tet. Oct. 2:1 Mineral: Talc, Mg3Si4O10(OH)2 Tet. Oct. Layer Build-up: Trioctahedral Phyllosilicate Minerals Sheets Tet.

  46. Mineral Mg2+ K+ Glycerol 550 C Kaolinite 7 7 7 - Mica 10 10 10 10 Vermiculite 14 10 14 10 Smectite 14-16 12-14 18 10 HIV 14 14 14 10-11 HIS 14-16 14 18 10-11 XRD: Chemical Treatment d-spacing, Angstroms

  47. Oct. Octahedral Minerals Brucite, Mg(OH)2 Gibbsite, Al(OH)3

  48. Serpentine: Mg3Si2O5(OH)4 - trioctahedral Kaolinite: Al2Si2O5(OH)4 - dioctahedral

  49. tet tet tet tet oct oct Micas Phlogopite: KMg3(AlSi3O10)(OH)2 Biotite: KFe3(AlSi3O10)(OH)2 Muscovite: KAl2(AlSi3O10)(OH)2 K+ K+ K+

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