Hydrolysis Example: Cleopatra’s Needle, New York (Fig. 6.7)
Hydrolysis takes place when hydrogen in water reacts with minerals in the rock creating a chemical reaction. Feldspar, which holds granite together, crumbles when it comes in contact with rainwater. This reaction leads to the formation of kaolin, a type of clay used in pottery.
DID YOU KNOW?
Quartz is a chemically resistant mineral, therefore it is not affected by hydrolysis.
Fig. 6.7 Before and after effects of hydrolysis on Cleopatra’s Needle, New York. EXAM LINK (HL)
Weathering (30 marks) Explain one process of physical weathering and one process of chemical weathering. 2016, Q1C
Marking Scheme:
Physical and chemical processes named = 2 marks + 2 marks Explanation of physical/chemical weathering = 6 SRPs × 2 marks + 7 SRPs × 2 marks
Biological weathering widens the joints in rocks. This allows water to penetrate further into the rock, which can lead to further weathering processes such as carbonation.
Biological Weathering
Processes Animals or plant roots can widen the spaces within or between rocks, causing them to break down. Animals such as rabbits can widen the crack in a rock through their burrowing, while plant roots push open the cracks making them wider and deeper as they grow bigger. Eventually the rock will weaken to the point where pieces will break away (Fig. 6.8).
