1. Mechanical versus chemical
weathering
Mechanical versus chemical

2. WEATHERING
Changes that occur in sediments and rocks near Earth’s surface
Two main types:
Chemical and Physical (Mechanical)

3. The breakdown of rock into smaller pieces or sediments.
What is weathering?
The breakdown of rock into smaller pieces or sediments.
Two Types of Weathering:
Mechanical – disintegration (smashing a rock with a hammer)
Chemical – decomposition of rocks due to chemical reactions (minerals become chemically altered, ex. Calcite reacting with acid)

4. Mechanical Weathering
Smashing a rock with a hammer
Rock is not altered, it is broken down to smaller pieces

5. Frost action
Pushing rock apart by alternate freezing and thawing of rock

7. exfoliation
cracking of rocks as they expand due to removal of overburden pressure

8. Exfoliation

9. Thermal expansion
cracking of rocks from alternate expansion and contraction due to daily changes in temperature (mostly found in the desert)

10. Wetting and drying
constant swelling and shrinking causes the rock to crack

11. abrasion
wind, waves, rain, glaciers, and so on abrade rocks’ surfaces, wearing them down

12. Organic activity
expansion of cracks by growth of roots and the breakup by burrowing processes

13. Mollusks live in small holes they scrape in the rocks

14. chemical Weathering Calcite reacting with acid
Minerals making up the rock are chemically altered

15. Plant acids
lichens secrete acids that dissolve rocks

16. oxidation
oxygen combines with mineral to break down and soften the original mineral

17. hydrolysis
hydroxide (oh) combines with minerals to break down and soften the original mineral, ex. Feldspar turns to clay

18. Sulfuric acid
minerals are dissolved by reaction with acid, ex. Acid rain

19. Effects of acid rain on cleopatra’s needle
(c. 1543–1292 BC)

20. carbonation
carbonic acids dissolve rocks and form caves underground

21. Rates of weathering
Chemical weathering most active in warm and moist climates where water is abundant
Mechanical processes are active everywhere and can be sped up by interacting with chemical weathering