Rocks: The earth’s crust is made up of rocks of various types. A rock is a natural piece of mineral matter that makes up the earth’s crust. Rocks can be of differnt:
The word igneous is derived from the Latin word Ignis which means fire. The rocks formed by the solidification on the cooling of molten magma, are called igneous rocks. Depending on where the molten magma cools, they are of the following types:
When the molten magma cools deep inside the earth’s crust, intrusive igneous rocks are formed. They
Granite is intrusive igneous rock.
Grinding stones used to prepare paste / powder of spices and grains are made of granite.
When the molten magma (lava) comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in such a manner on the crust are called extrusive igneous rocks. They have a very fine grained structure. Basalt is an example of extrusive igneous rocks.
The Deccan Plateau is made up of basalt rocks.
These rocks get their name from the Latin word sedimentum which means settle down. These rocks are formed by the settling down of sediments. Sediments are the smaller particles / fragments that are formed by the breaking down of rocks when they roll down, crack and hit each other. These sediments are transported by wind, water etc. These sediments; when compressed and hardened; form sedimentary rocks.
Sandstone is an example of sedimentary rock. It is made up of grains of sand. The sedimentary rocks may also contain fossils of plants, animals and other micro – organisms that once lived on them.
The Greek word ‘metamorphose’ which means change of form, is the root of the word metamorphic. In other words, these are the rocks that are formed when the igneous and sedimentary rocks change their form under the following two circumstances:
The following are the examples of metamorphic rocks:
A cyclic manner is followed in transformation of one type of rock to another type under certain conditions. This process of transformation of the rock from one to another is called the rock cycle.
Fig: Rock Cycle
Rocks are made up of different minerals. Minerals
Lava: Fiery red molten magma coming out from the interior of the earth on its surface.
Fossils: The remains of dead plants and animals trapped in the layers of rocks.
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