1. Weathering

2. Weathering Chemical Weathering Products and Forms Made by Weathering
Weathering vs. Erosion
Joints: Setting the Stage
Physical (Mechanical) Weathering
Chemical Weathering
Products and Forms Made by Weathering
Weathering Landscapes

3. Physical weathering “sets up” chemical weathering

4. Why do you ground coffee? to increase surface area

5. 4. Chemical Weathering
Egyptian Obelisk – chemically weathered when brought to wetter environment, so water matters!

6. Video Presentations This clip introduces chemical weathering.
This clip is another introduction to chemical weathering.

7. Dissolution Sugar & Salt Dissolves – so do rocks
Best example: limestone

9. Other rocks dissolve too, but slower than limestone

10. Acid Rain Accelerates Decay
Crosses political boundaries …

11. Athens
Taj Mahal

12. Short Clip
Play this short clip of HCl dropped on carbonate

13. Oxidation

14. Hydrolysis H+
Water molecules at the mineral surface dissociate into H+ and OH- and the mobile H+ ions penetrate the crystal lattice, creating a charge imbalance, that causes cations (important nutrients) such as Ca2+ , Mg2+, K+ and Na+ to diffuse out. For example, the feldspar reacts to decay and leaves a residue of clay mineral.
OH- H+

15. Hydration Complexation Water alters structure
Metals released from primary minerals such as iron and manganese build complexes with organic components, such as fulvic acids and humic acids, causing an imbalance between cations and anions – that leads to mineral decay

16. Online Animations Chemical Weathering Visualizations

17. 5. Products and Forms Made by Weathering – lots!!
Quartz Sand: quartz is one of the last minerals to decay – it survives weathering & erosion to be deposited in

18. Rock Coatings are products of weathering
Rock Coatings are products of weathering. Almost every rock you see is coated.
Natural Rock Coatings
Anthropogenic rock coatings
Case Hardening
Salt Efflorescence & Subflorescence

19. Natural Rock Coatings

20. Some natural coatings can be identified in the field and in photographs you will see
Lithobionts
Rock varnish
Droppings
Dust coatings
Iron film

21. Lithobiont Natural Coatings

22. Rock varnish

23. Bird droppings

24. Dust Coatings

25. Iron Films (often with others)

26. Hard to identify in the field
Silica glaze
Heavy metal coatings
Oxalate crusts

27. Silica Glaze

28. Rock coating detachment

29. Anthropogenic rock coatings

30. Case Hardening

31. Another product of weathering Plant Nutrients - released from mineral weathering
Calcium (Ca)
Sodium (Na)
Magnesium (Mg)
Potassium (K)

32. Clay Minerals Formed

34. Clays represent Earth’s ultimate decay of rock

35. If have too much clay, it shrinks & swells

36. Shrink-swell of clays can disturb the foundations of homes

37. Weathering can make rocks less hard
Mohs Scale of Hardness
1 – talcum powder
2.2 – fingernail
3 - calcite
5.5 – knifeblade
7 – quartz
10- diamond

38. Other small things you see – erosion set up by weathering: lithobiont pitting

39. When Lithobionts die: like breaking a dam – quick erosion

40. Splintering: like wetting a book

41. Splintering destroys rock surfaces

42. Differential weathering can highlight textural anomalies
Banding
Concretions
Mafic inclusions

43. Imagery seen in this presentation is courtesy of ASU faculty, Paradise Valley and Mesa CC faculty, students and colleagues in other academic units, individual illustrations in scholarly journals such as Science and Nature, scholarly societies such as the Association of American Geographers, city, state governments, other countries government websites and U.S. government agencies such as NASA, USGS, NRCS, Library of Congress, U.S. Fish and Wildlife Service USAID and NOAA.