History and development of soil science, its scope and importance
- 3. From where do mineral particles originate?
- 4. Rocks and Minerals Limestone Calcite Sandstone Quartz Shale Clays Granite Quartz/Feldspars Basalt Quartz/Feldspars Rock Dominant Mineral
- 5. Weathering Physical: changing the size and shape of Rocks or mineral particles without altering their chemical composition Chemical: altering a mineral particle’s chemical composition.
- 6. Weathering Physical: freezing and thawing plants and biota wind, rain, abrasion Chemical: hydration hydrolysis oxidation/reduction acids dissolution Reduce Size } Chemical Alteration } Destruction and Synthesis
- 7. Minerals: quartz, feldspars, biotite Granite
- 8. Rocks breakdown (weather) by physical means Primary Minerals Primary minerals (e.g. quartz, feldspars) are dominated by Si, Al, O Primary minerals breakdown (weather) principally by chemical means Secondary Minerals Silicate clay minerals are dominated by Si, Al, O Silicate clays Iron oxides Aluminum oxides
- 9. Quartz SiO2 Feldspar KAlSi3O8 Biotite KMg3AlSi3O10(OH)2 Albite NaAlSi3O8 Muscovite KAl3Si3O10(OH)2 Primary Minerals Aluminum and Silicon
- 10. Quartz SiO2 Feldspar KAlSi3O8 Biotite KMg3AlSi3O10(OH)2 Albite NaAlSi3O8 Muscovite KAl3Si3O10(OH)2 Chemical Alteration and Reorganization Primary Minerals Crystalline Aluminosilcate Clays Dominated by Aluminum, Silicon, Oxygen Chemical weathering Secondary Minerals
- 11. Silicate Clays
- 12. Silicate Clays Colloidal 1.Small (< 1 micron) 2.Large surface area 3.Highly reactive
- 13. Constituents of Silicate Clays Si4+ Al3+ Aluminosilicates O2- OH- These 4 ions are arranged together to form crystals with a number of important properties related to soil reactivity.
- 14. Silicate Clay minerals are crystalline and formed by specific arrangement of ionic forms of Si, Al, and O Ions are stable forms of elements that possess an electrical charge. Cations are elements that have lost electrons to become (+) charged Anions are elements that have gained electrons to become (-) charged.
- 15. Building a Crystal with Cations and Anions
- 16. Crystalline Mineral Colloids Si4+ Al3+ Aluminosilicates O2- OH- Cations and Anions
- 17. oxygen silicon (Si4+) hydroxide (OH-) Aluminum (Al3+) Silicon Tetrahedron Aluminum octahedron Building Blocks for Silicate Clays
- 18. Graphite Diamond Crystalline Minerals Fundamental Building Blocks Fundamental Building Blocks Silicon Tetrahedron Aluminum Octahedron Oxygen (O2-) silicon (Si4+) Hydroxide (OH-) Aluminum (Al3+)
- 19. Tetrahedra Tetrahedra and and Octahedra Octahedra Sharing the Sharing the Oxygens Oxygens Linkage of thousands of silica tetrahedra and aluminum octahedra O Si O, OH Al OH Tetrahedra octahedra { { 1:1 Mineral
- 21. 1:1 minerals 2:1 minerals
- 23. Electrical Properties of Soil Minerals
- 24. Positive charge Al3+ Si4+ Negative charge OH- O2- Charge Balance Al3+ Si4+ OH- O2- =
- 25. Uncharged silicate clay minerals Talc Pyrophillite AlSi2O5OH. +3 2 x (+4) = +8 5 x (-2) = -10 -1 Total = zero Positive Charge Al3+ Si4+ Negative Charge O2- OH-
- 26. Isomorphous Substitution Substitution of lower-charge cations for higher charge cations during mineral formation. Al3+ for Si4+ in tetrahedra Mg2+ for Al3+ in octahedra The result is a deficit of positive charge or a surplus of negative charge in the mineral structure.
- 27. Tetrahedral Substitution Al3+ for Si4+ Positive Charge = Negative Charge
- 28. Octahedral Substitution Mg2+ for Al3+ Positive Charge = Negative Charge
- 29. Tetrahedral Substitution Octahedral Substitution Al3+ for Si4+ Mg2+ for Al3+