6. Types of Mechanical
Weathering
2) Unloading
- caused by a decrease in
pressure
- effective on large bodies of
intrusive igneous rocks
7. Unloading
Rocks expand & crack parallel to
surface (“sheeting”)
- produce rounded mountains
called exfoliation domes
Ex: Yosemite National Park, CA
Stone Mountain, GA
11. Types of Mechanical
Weathering
3) Abrasion
- grinding by friction
- usually done by water: rivers,
waves, glaciers
- process by which rivers & glaciers
carve their own valleys
14. Types of Weathering
Processes
2) Chemical Weathering
- alters crystalline structure and/or
composition of minerals
- new minerals formed or minerals
dissolve
17. Agents of Chemical Weathering
2) Acid – destroys crystalline
structure
Ex: How granite weathers (p. 89)
Feldspar + acid = clay mineral
Clay minerals = most common
weathering product of silicates
18. Clay Minerals
Family of minerals
Microscopic sheet silicates (like
mini-micas)
Ex: kaolinite
21. Sources of Acid
b) Mine Drainage
- sulfur-bearing minerals react with
water to form sulfuric acid
Ex: Pyrite = FeS2 (iron sulfide)
Galena = PbS (lead sulfide)