Here's why:
* Chemical weathering involves chemical reactions that break down the minerals within rocks. This can happen through processes like:
* Oxidation: The reaction of minerals with oxygen, often forming oxides (like rusting).
* Hydrolysis: The reaction of minerals with water, breaking down the mineral structure.
* Carbonation: The reaction of minerals with carbonic acid (formed when carbon dioxide dissolves in water), often dissolving minerals like calcite.
* Acid rain: Rainwater that is acidic due to pollutants can also chemically break down rocks.
* Physical weathering breaks rocks down into smaller pieces without changing their mineral composition. Examples include:
* Frost wedging: Water freezing in cracks and expanding, putting pressure on the rock.
* Abrasion: Rocks rubbing against each other, wearing them down.
* Thermal expansion/contraction: Rocks expanding and contracting due to temperature changes.
In summary: While physical weathering alters the size and shape of rocks, it's chemical weathering that actually changes the minerals within the rocks themselves.
