Chemical and biological weathering lesson 5

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Chemical and biological weathering lesson 5

  1. 1. CHEMICALWEATHERING
  2. 2.  Decomposition of rock in situ resulting from chemical change Water (rain, fog, moisture, ocean etc) is the key medium for chemical weathering. Common in warm humid climate (high temperature & high rainfall) Weathered rocks by this process have a dull pitted appearance
  3. 3. 1. Oxidation2. Hydration3. Hydrolysis4. Carbonation5. Solution
  4. 4.  Oxygen dissolved in water reacts with mineral iron in the rock The rock is converted to iron oxide Always seen as reddish- brown crust This conversion weakened the mineral bonding and consequently the whole
  5. 5.  Involves in the expansion of minerals resulting from the absorption of water E.g. Clay minerals are capable of absorbing large quantities of water into their crystal structure When this happen, they exerts stresses within the rock which may eventually cause it to break apart
  6. 6.  Involves a chemical reaction between hydrogen ions in water with certain minerals in the rock E.g. Weakly acidic rainwater causes feldspar to be converted into white powdery clay (kaolin) which breaks down easily
  7. 7. Hydrolysis
  8. 8. Kaolinite mine
  9. 9.  Is a form of solution weathering Common in rocks composed of calcium carbonate such as limestone and chalk Rainwater mixed with carbon dioxide form carbonic acid The acid water change the calcium carbonate to soluble calcium bicarbonate which is then easily washed away
  10. 10.  Simply the dissolving minerals in water E.g Halite (rock salt) dissolve in water Quartz dissolves at an extremely slow rate
  11. 11. Spheroidical Weathering A type of chemical weathering Creates rounded boulders and domed monolith Typically granitic in composition Rock forms at great temperatures and pressures
  12. 12. BIOLOGICALWEATHERING
  13. 13.  Caused by the action living organisms Can lead to physical break down of rock (Biophysical) Also chemical attack (Biochemical weathering)
  14. 14. 1. By plant roots2. By animals such as rodents and earthworms3. By human activities
  15. 15.  By plant roots:  When roots penetrate into cracks, they will usually break rocks apart
  16. 16.  By animals:  Help to widen and loosen the joints in rocks and expose underlying rocks to weathering processes as they burrow through the ground
  17. 17.  By human activities:  Clearing of land for cultivation  Construction and mining activities  This activities break up rocks and expose them to the weathering
  18. 18.  Organic acids from dead plants and root can help to decompose rock Chelation is the effect of organic acid on rock Waste and organic acids from dead animals help to weather rocks chemically
  19. 19.  Human activities:  Industrialisation can cause pollution such emission of sulphur dioxide which can produce acid rain  Accelerate the chemical weathering process of hydrolysis, carbonation and solution

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