Chemical weathering occurs when rocks undergo chemical reactions to form new minerals. Water, acids, and oxygen are just a few of the chemicals that lead to geological change. Over time, chemical weathering can produce dramatic results.
Chemical Weathering From Water
Water causes both mechanical weathering and chemical weathering. Mechanical weathering occurs when water drips or flows over rock for prolonged periods; the Grand Canyon, for example, was formed to a large degree by the mechanical weathering action of the Colorado River.
Chemical weathering occurs when water dissolves minerals in a rock, producing new compounds. This reaction is called hydrolysis. Hydrolysis occurs, for example, when water comes in contact with granite. Feldspar crystals inside the granite react chemically, forming clay minerals. The clay weakens the rock, making it more likely to break.
Water also interacts with calcites in caves, causing them to dissolve. Calcite in dripping water builds up over many years to create stalagmites and stalactites.
In addition to changing the shapes of rocks, chemical weathering from water changes the composition of water. For example, weathering over billions of years is a big factor in why the ocean is salty.
