1. Soil Mineralogy and Chemistry Lecture 4

3. Phyllosilicate Minerals

4. tet oct tet oct tet oct tet oct tet oct trioctahedraldioctahedral octahedra 1:1 2:1 T:O (class) brucite gibbsite serpentine kaolinite pyrophyllite talc Phyllosilicates, NO layer charge

5. Building of Tetrahedral Sheets * Linked SiO 4 tetrahedra

6. SiO 4 Tetrahedron

7. x y z

8. Si 6 O 18

9. Linking Rings to Form Tetrahedral Sheets

10. Tetrahedral Sheet Si:O 2:5

11. Building of Octahedral Sheets

12. Al(OH) 6 or Mg (OH) 6 Octahedra OH

14. Octahedral Sheet OH

15. A Georgian Ultisol

16. Octahedral-Tetrahedral Linkage

17. Sharing of Apical Oxygens in Tetrahdral Sheet with Hydroxyls of Octahedral Sheet Serpentine (1:1 trioctahedral mineral) tet oct

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

19. tet oct Short hand, Block notation Short-hand Symbols

20. tet oct tet oct tet oct tet oct tet oct trioctahedraldioctahedral octahedra 1:1 2:1 T:O (class) brucite gibbsite serpentine kaolinite pyrophyllite talc Phyllosilicates, NO layer charge

21. Isomorphic Substitution  permanent (layer) charge Charge Development

22. Al 3+, Fe 3+ Si 4+ tet oct Mg 2+ Al 3+ Isomorphic Substitution

23. -------------- -------------- ++++++++++++++ -------------- -------------- ++++++++++++ Isomorphic substitution NET Charge 0 -2

24. Terminal Bonds  pH-dependent charge (ionizable functional groups) Charge Development

25. terminal bonds Terminal Bonds

26. Terminal Bonds: Ionizable Functional Groups Al-OH 2 +  Al-OH o + H +  Al-O - + H + Al O High pH Low pH -pH-dependent charge - edges of phyllosilicates; all surface on Fe- and Al-oxides

27. tet oct tet oct tet K+K+ K+K+ K+K+ Phyllosilicates: 2:1 with layer charge micas 1 unit of (-) layer charge per formula unit tet oct tet oct tet K+K+ H2OH2O Ca 2+ H2OH2O H2OH2O < 1 unit of (-) layer charge per formula unit 2:1 clay minerals

29. Swelling Potential?

30. Structure d-spacing Interlayer Status: d-spacing (and mica) K+K+

31. CEC cmol/Kg Properties of Clay Minerals

32. Western GA Ultisol Kaolin and Oxide Rich Soil Accessory Minerals

33. Smectite Soil NE Montana Vertisol Hawaiian Oxisol Iron and Al-oxide Rich ?

35. Young, weakly weathered soils = fine-grained mica, chlorite, vermiculite (Entisol, Inceptisol) Intermediate weathering = vermiculite, smectite, kaolinite (Mollisol, Alfisol, Ultisol) Strong weathering = kaolinite, hydrous oxides (Ultisol--> Oxisol) Clay mineralogy reflects weathering processes Micas  Vermiculite  Smectite  Kaolinite  Al,Fe-Oxides

36. Mol Alf Ult E/I

37. Organic Matter - reactive functional groups: carboxyl, hydroxyl, phenolic * Humus, Humic Acid, Fulvic Acid

38. + Flocculation (chemical) Aggregation Flocculation and Aggregation (organic gluing)

39. Organic Matter Promoted Aggregation