Notes On Rocks and Minerals - CBSE Class 7 Geography
A rock is a natural mass of minerals found within the earth’s crust while minerals are substances that have a definite chemical composition and occur freely in nature. Rocks can be are classified in three types on the basis of their texture and the process of formation i.e. igneous, sedimentary and metamorphic rocks. The igneous rocks are formed when molten lava from a volcano cools down. These rocks are also known as primary rocks as they are the first to be formed and are further of two types: extrusive and intrusive. Extrusive igneous rocks are formed when magma flows out on to the earth’s surface and cools down rapidly by air to form solid fine-grained rocks. Intrusive igneous rocks are formed when molten magma cools down inside the earth’s crust. Sedimentary rocks are formed by the sedimentation or deposition of smaller rock particles in layers called beds or strata. The smaller particles formed from these large rocks are called sediments.  Sometimes, during formation, sedimentary rocks may contain preserved remains of plants and animals trapped within the layers. These remains are called fossils. Metamorphic rocks are formed when igneous and sedimentary rocks undergo great heat and pressure over time.

#### Summary

A rock is a natural mass of minerals found within the earth’s crust while minerals are substances that have a definite chemical composition and occur freely in nature. Rocks can be are classified in three types on the basis of their texture and the process of formation i.e. igneous, sedimentary and metamorphic rocks. The igneous rocks are formed when molten lava from a volcano cools down. These rocks are also known as primary rocks as they are the first to be formed and are further of two types: extrusive and intrusive. Extrusive igneous rocks are formed when magma flows out on to the earth’s surface and cools down rapidly by air to form solid fine-grained rocks. Intrusive igneous rocks are formed when molten magma cools down inside the earth’s crust. Sedimentary rocks are formed by the sedimentation or deposition of smaller rock particles in layers called beds or strata. The smaller particles formed from these large rocks are called sediments.  Sometimes, during formation, sedimentary rocks may contain preserved remains of plants and animals trapped within the layers. These remains are called fossils. Metamorphic rocks are formed when igneous and sedimentary rocks undergo great heat and pressure over time.

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