Class Notes: Geo 1330: Dr Dupre

Weathering

________________: The in-situ alteration of rocks at or near the surface

_________________: The transfer of rock and soil down-slope by gravity

_________________: The physical removal of material by mobile agents (e.g. water, wind, or ice)

The two types of weathering are:

1) _________ (or physical) weathering

2) _________ weathering

______________ Weathering: the disintegration or breaking up of rocks without changes in the composition of weathered products.

______________ Weathering: the decomposition of rocks causing changes in the composition of weathered products.

Selected Processes of ______________Weathering:

1) _______________ (results in exfoliation sheets)

2) _______________

3) _______________

4) _______________ (?)

Selected Processes of _____________Weathering:

1)

2)

3)

4)

 Figure 6.4

Figure 6.3

Figure 6.8

Figure 6.7

Selected Processes of Chemical Weathering:

___________________: A chemical process in which a solid is completely dissolved into ions by an acid. e.g. dissolution of Halite or Calcite

Dissolution of Halite (Fig. 6.9)

NaCl = Na⁺ + Cl^- + H₂O

Dissolution of Calcite

CaCO₃ + H⁺ = Ca⁺⁺ + CO₂ + H₂O

Calcite + Acid = Calcium + CO₂ +Water

Where does the acid come from?

H₂O + CO₂ = H₂CO₃= H⁺ + [ HCO₃]^-

Water + CO₂ = Carbonic Acid

Examples

 Acid Rain (GEODe)

____________________: A chemical process in which water is incorporated within the mineral structure . e.g.

CaSO₄ + 2(H₂O) = CaSO₄• 2H₂O

anhydrite + water = gypsum

Etched and corroded feldspar in the soil zone.

_______________: A chemical process in which a H⁺ ion replaces other cations in a mineral. e.g. alteration of feldspars à clay

How is chemical weathering like making coffee??

In warm, temperate climates:

K-feldspar + carbonic acid + water à __________ (clay) + ions in solution

Under extreme chemical weathering conditions (e.g. the Tropics), hydrolysis can remove all of the available cations, leaving behind only "_____________" Al(OH)₃ (the ore for Aluminum)

_________________: A chemical process in which a compound loses an electron, usually to an Oxygen ion. e.g. oxidation of Iron to form an Iron Oxide (such as rust)

Acid Mine Drainage (figure 6.11)

Oxidation of Pyrite (not balanced)

FeS₂ + O⁴⁺ à FeO(OH) +H₂SO₄

Pyrite + Oxygen à Limonite + Sulfuric Acid

What controls the rate of chemical weathering?

1) ________________

2) ________________

3) ________________

 Weathering Stability Series (figure 6.15)

Why are minerals that form at the highest temperatures most chemically unstable under atmospheric conditions?

Relative stability of Common Minerals

In what climate would you find chemical weathering dominant and why?

In what climate would you find mechanical weathering dominant and why?

Role of climate in weathering Feldspar

• Feldspar (dry climate)

• Kaolinite (moderate, temperate climate)

• Bauxite (extreme tropical climate)

Role of climate in weathering Granite:

What are the weathering products of Granite in a temperate climate?

What are the weathering products of Granite in an arid climate?

Products of Weathering (table 6.1)

Original Mineral Weathers to produce Released in Solution

Role of Joints in Weathering (figure 6.6)

How does the intensity of fracturing change the Surface Area/Volume ratio, and why is it important to rates of weathering?

Figure 6.2

 .

 Spheroidal Weathering (figure 6.12):

Examples of Differential Erosion

Weathering Rates of Gravestones (figure 6.14)

In Humid Climates:

• ___________ ---à ridges and cliffs

• ___________ ---à valleys and slopes

• ___________ ---à valleys and slopes

In Arid Climates:

• ___________ ---à ridges and cliffs

• ___________ ---à valleys and slopes

• ___________ ---à ridges and cliffs

How to make a Sedimentary Rock

1) Weathering of pre-existing rock

2) Mass Wasting and/or Erosion of weathering by-products

3) Transportation of weathering by-products

4) Deposition or Precipitation to form Sediment

5) Lithification of sediment to form Sedimentary Rock