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CH3041
SILICATE WEATHERING
• Bowen’s series predicts which silicates will be found unaltered in a soil. Incomplete acid hydrolysis is common in altered minerals. 
2NaAlSi3O8(s) + 2H2CO3 +9H2O    ®
  2Na+ + 2HCO3- + 4H4SiO4(aq) +  Al2Si2O5(OH)4(s)
Na-feldspar            ®                     kaolinite (clay)
• The surface of a crystalline mineral will
have many imperfections. This results in
areas of high surface charge;
-ve charged surface regions
are attacked by H+ causing
pits to develop.
• eg. Feldspar.
• River [H4SiO4(aq]average 14ppm