I. Chemical Weathering Process

No rock-forming mineral is absolutely chemically inert; some are more readily altered than others. A variety of chemical actions such as carbonation, hydration, oxidation and reduction act on the rocks to decompose and dissolve them. Water, air (Oxygen and carbon dioxide) along with heat must be present to speed up all chemical reactions. Biological activities such as decomposition of plants and animals increase acidity and other elements in the crust which enhances chemical weathering.

♤ Hydration: is a process by which certain types of mineral expand as they take up water and expand, causing additional stresses in the rock due to increase in the volume of mineral itself. For instance, calcium sulphate absorbs water and turns to gypsum. Decomposed products of rock-forming minerals are also subjected to hydration, thereby accelerating the disintegration of the rock. This process of hydration is reversible and continued repetition

causes fatigue in the rock which eventually may lead to cracking of overlaying materials and finally disintegration.

♤ Oxidation and reduction: oxidation is the addition of oxygen to form oxides or hydroxides while reduction is the reverse of oxidation. Oxidation occurs when mineral has access to atmosphere or oxygenated water. To put it simply, they rust. Red color of iron turns to brown upon oxidation.

♤ Solution: few minerals such as rock salt are significantly soluble in water. Such rock-forming minerals are easily leached out without leaving any residue in rainy climates and accumulate in dry regions. Minerals like calcium carbonate present in limestones are soluble in water containing carbonic acid. Carbon dioxide produced by decaying organic matter along with soil water greatly aids in this reaction.

♤ Carbonation: many minerals are soluble in rainwater, which contains carbon dioxide and acts as a weak carbonic acid. This is particularly important in the decomposition of limestones; the rain water converts the calcium carbonate into calcium bicarbonate, which is soluble and can be taken away in the groundwater.

These weathering process are inter-related. Hydration, oxidation, carbonation etc. go hand-in- hand and hasten the weathering process.