Chemical Weathering

• Carbonation

  • This attacks calcium carbonate in limestones, other carbonate rocks and sedimentary rocks with calcite sediment. 
  • Rainwater mixed with carbon dioxide from the air to form weak carbonic acid (pH 5.6). 
  • The acidic rain mixes with calcium carbonate to form soluble calcium bicarbonate solution. 
  • 'Rock disappears' as new minerals dissolve into the solution. 
  • Only sediment left from limestone is clay particles that had formed impurities in the original rock. 
  • Where calcite sediment is weathered, previously cemented clasts are released to form sediment. 
• Hydrolysis  


  • The breakdown of minerals to form new clay minerals, plus materials in solution, due to the effect of water and dissolved carbon dioxide. 
  • Rocks vulnerable to it are: igneous and metamorphic rocks containing feldspar and other silicate minerals 
  • This attacks the feldspar (pinky) minerals in granite
  • H+ ions in water attack the feldspar minerals forming kaolin clay cement
  • Bonds between feldspar and quartz minerals are broken, releasing quartz grains as sand sediment.