Rock weathering

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.