Chemical and biological weathering lesson 5

1. CHEMICAL WEATHERING

2. Chemical Weathering 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. Five main processes of chemical weathering Oxidation Hydration Hydrolysis Carbonation Solution

4. Oxidation 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 structure of the rock

5. Hydration 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. Hydrolysis 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. Hydrolysis

8. Kaolinite mine

9. Carbonation 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. Solution Simply the dissolving minerals in water E.g Halite (rock salt) dissolve in water Quartz dissolves at an extremely slow rate

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. Spheroidal weathering

13. BIOLOGICAL WEATHERING

14. Biological Weathering Caused by the action living organisms Can lead to physical break down of rock (Biophysical) Also chemical attack (Biochemical weathering)

15. Biophysical Weathering By plant roots By animals such as rodents and earthworms By human activities

16. Biophysical By plant roots: When roots penetrate into cracks, they will usually break rocks apart

17. By animals: Help to widen and loosen the joints in rocks and expose underlying rocks to weathering processes as they burrow through the ground Biophysical

18. By human activities: Clearing of land for cultivation Construction and mining activities This activities break up rocks and expose them to the weathering processes Biophysical

19. Biochemical 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

20. 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 Biochemical