English PSSSB Practice 24

Rocks are the solid natural substances that form the Earth's crust and provide the foundation for landscapes, soils, and mineral resources. They are composed of one or more minerals and are classified into three major types based on their origin: igneous, sedimentary, and metamorphic. Igneous rocks are formed from the cooling and solidification of molten magma or lava. When magma cools slowly beneath the Earth's surface, it forms intrusive igneous rocks such as granite and gabbro, which have large crystals. When lava cools quickly on the surface, it forms extrusive igneous rocks such as basalt and pumice, usually fine-grained or glassy in texture. Sedimentary rocks are formed by the accumulation and compaction of sediments, which may include fragments of other rocks, minerals, and organic remains. They are deposited in layers and often contain fossils that provide evidence of past life and environmental conditions. Common examples include sandstone, limestone, shale, and conglomerate. Metamorphic rocks are produced when existing igneous or sedimentary rocks are subjected to high heat, pressure, or chemical processes within the Earth's crust, leading to physical and chemical changes. Examples include marble (from limestone) and slate (from shale). Rocks are not static; they continuously change from one type to another in a process known as the rock cycle. For instance, igneous rocks can break down into sediments and form sedimentary rocks, which under pressure and heat may transform into metamorphic rocks, and metamorphic rocks can melt again to form magma, restarting the cycle. Rocks are economically and environmentally significant as they provide construction materials, metals, fuels, and fertilizers. They also influence landforms, soil fertility, and groundwater storage. In geography, studying rocks helps us understand Earth's history, the processes shaping its surface, and the resources on which human civilization depends. Thus, rocks are not only the building blocks of the planet but also a key to interpreting its dynamic past and sustainable future.