Home | Session 4 | Weathering Pg 1, 2, 3, 4

Weathering and Erosional Processes

Presented by Lisa White
San Francisco State University

Chemical weathering of igneous rocks, silicates

Feldspar + water ---------> Kaolinite (clay) or Montmorillonite

	Feldspar, biotite and magnetite grains commonly occur in igneous rocks
	Cracks form along crystal boundaries
	Cracks open and original minerals decay extensively to clays

Chemical weathering of carbonates:

• Calcite dissolves in a weak solution of carbonic acid , such a rainwater
  
  
  

  Calcite + Carbonic Acid	------>	Calcium Ion + Bicarbonate Ion
  CaCO3 + H2CO3		Ca2+ and 2HCO3-

Rates of Weathering on an Obelisk:

Obelisk in Middle East	Obelisk in NYC

What might have contributed to the difference?

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updated March 6, 2002

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