Chemical weathering refers to the breakdown of rock by chemical reactions that result in a change in the composition of the rock. This process can occur several ways.

• Hydrolysis: Water can directly react with many different minerals in rock. This reaction between water and minerals is known as hydrolysis. This chemical reaction results in the original rock being transformed. Water, for example, will react with feldspar, changing it into a common clay called kaolin.

• Oxidation: The reaction of metallic elements with oxygen is known as oxidation. Iron (Fe), for example, will react with oxygen (O₂) to form iron oxide (Fe₂O₃). The reddish color in certain soils is often due to the presence of iron oxide.

• Carbonation: Carbonation is the process whereby carbon dioxide reacts chemically with minerals in rocks. Carbon dioxide (CO₂) will combine with water (H₂O) to form weak carbonic acid (H₂CO₃). Carbonic acid can slowly dissolve limestone, producing caves and caverns as a result.

• Acid Rain: Human activity has resulted in the release of large quantities of gases into the atmosphere. These gas compounds can combine with water, and return to the Earth as rain that is slightly acidic. Sulfuric (H₂SO₄), nitric (HNO₃), and carbonic acid (H₂CO₃) can all be components of acid rain. Rain that is slightly acidic has a greater ability to weather rock than just ordinary rain.