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Chemical Weathering
- Decomposition of rocks due to change in chemical composition.
- Carbonation or solution
o Water reacts with CO2 to form carbonic acid.
o This acid dissolves rocks like limestone and dolomite.
o When this acid seeps into cracks or joints, the sides of the joints are dissolved.
o Resulting in deepened joints called grikes.
o As the joints become wider and deeper, a series of block known as clints are formed.
o E.g. Malham Yorkshire, UK
o Carbonation can lead to the formation of limestone caves. [ Massif Central, France]
§ In the caves, structure known as stalagmites[from the cave floor] and stalactites [ from cave ceiling] form
§ Made from calcium carbonate and are formed from years of evaporation of the water from the solution of dissolved limestone.
§ Over time, these structures connect to form pillars.
- hydrolysis
o no acids required
o takes place when water reacts with minerals in the rocks.
o As a result, the minerals are chemically altered
o This causes the rocks to weaken. And fall apart into finer pieces
o Granite – combination of feldspar, quartz and mica
o When water reacts with theses minerals, the less resistant feldspar reacts with water to form kaolin. This weakens the overall structure of the rock.
- hydration
o similar to hydrolysis in a way that minerals react with water.
o However, in this case, this leads to a swelling of the minerals which exert pressure n the rock the minerals are in.
o This eventually weakens the rock and leads to its disintegration
- oxidation
o takes place when rocks react chemically with the oxygen in the air.
o Esp in rocks witch contain iron.
o Oxygen I the air causes the iron to rust
o The rusting weakens the entire structure of the rock,
o Rocks which are oxidized disintegrate readily as the entire rock structure has been weakened
o It often takes place with hydrolysis which speeds up the process.
- Spheroidal weathering [ diff to understand.]
o Igneous rocks often contain many joints,
o These joints divide the rocks into angular blocks
o Rainwater passes through the rock via its joints.
o As more rainwater flows thorough the joints, the blocks of rock weather on all surfaces and become rounded as the minerals in the rock dissolve in water.
o Over time, the outer layer of weathered rock [rock which have already been disintegrated] becomes thicker while the core diminishes and becomes more spheroidal
o When the weathered rocks are washed off, the core is exposed
o Spheroidal rocsk known as corestones.
o Process forming these corestones known as spheroidal weathering


*in conclusion, chemical weathering often involves the presence of another substance such as air or water to react with minerals in the rock and

*physical weathering is often concerned with applying pressure on the sides of a joint in the rock and splitting the rock apart. It often has to do with a force usually pressure. So as long as u see pressure involved is physical weathering.