Solution: It is the chemical process in which the soluble minerals are dissolved by water entering into rocks through crevices. The dissolved minerals are removed with the flow of water resulting in the break up of the rock. Rock-salt and gypsum weather away chemically because of this process. Since silica is highly soluble in water, and silica is found in so many rocks, this process is also known as Desilication.
Hydration: It is the process by which some minerals in crystalline form absorb water and become a powdery mass. Feldspar, a common rock-forming crystalline mineral absorbs water and becomes a mass of clay by the process of hydration. The other minerals present along with feldspar get separated into loose particles and the rock breaks up.