# Rock weathering

Source: https://projectgcse.co.uk/chemistry/rock_weathering

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- Weathering is the process by which all rocks at the earth's surface gets broken down.
- Physical weathering - Rock gets broken into pieces but its chemical composition remains unchanged.
- 3 types are: - 1) Freeze / thaw weathering - occurs when temperature freezes at night and rises during the day. Water expands when frozen which forces rocks open. - 2) Biological weathering - Roots of plants grow into cracks and force cracks open. - 3) Exfoliation - when rock at earth's surface is worn away. A mass of igneous rock may be exposed which expands upwards forming a dome. As it expands it breaks into sheets parallel to the surface.
- Chemical weathering - Rock broken down by chemical change - water always plays a part e.g. Carbon dioxide dissolves in rain water forming carbonic acid which dissolves limestone rock which is carried away in solution as calcium hydrogen carbonate.
- Chemical weathering is faster for limestone than sandstone and is speeded up by heat.
- Chemical weathering occurs fastest at the sharp edges of rocks as they have a large surface and less volume so they can be eroded quicker.
- Chemical weathering produces clays on which vegetation can grow. A mixture of dead vegetation and clay produces soil which contains the minerals plants need.
- Physical and chemical weathering occur together. Physical breaks rocks into pieces so more surface is exposed to chemical weathering which breaks it down further.