Changes Around Us: Physical and Chemical — Science STD 7 — Question

Weathering is the process by which rocks are broken down into smaller pieces, eventually forming soil. It occurs through both physical and chemical changes. Physical weathering occurs when large rocks break into smaller pieces without changing their chemical composition. This can be caused by change in temperature due to climate, the growth of tree roots, or the freezing of water within cracks in the rocks. Chemical weathering happens when water or chemicals in the water react with the minerals in rocks, changing their composition. For example, a black coloured rock called basalt, which contains iron, undergoes a chemical change. When exposed to water or moist air for a long time, the iron reacts with oxygen to form iron oxide, which gives the rock a red colour.