Deep below the lithosphere, is a mass of hot, molten rock material. This is known as magma. Magma solidifies under various conditions to form igneous rocks. Ignis is the Latin word for fire. The magma that comes to the surface of the Earth and solidifies forms fine-grained rocks like basalt. Basalt is a dark-colored igneous rock. Granite and Basalt are widely used for the construction of roads and buildings.
All rocks on the Earth’s surface are worn down by wind, water, ice and other agents. They are broken into smaller pieces to form pebbles, gravel, sand and silt. These materials along with organic remains get deposited in low-lying areas like the beds of the sea, river and lake. These deposits or sediments are pressed together or cemented together to form sedimentary rocks. Such rocks include sandstone, shale, limestone and clay.
Almost three-fourths of the Earth’s surface is covered by sedimentary rocks. They often contain the remains of plants and animals.
Rocks, which under tremendous heat and pressure are completely changed or metamorphosed from their original form, are called metamorphic rocks. The new rock is completely different from the original. Metamorphic rocks are very hard and usually found in old plateau regions. Examples of metamorphic rocks are gneiss, marble and quartzite, which have been metamorphosed from granite, limestone and sandstone. Coal gets transformed into diamond.
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