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The Igneous rocks are the oldest type of rocks among all. The word “Igneous” comes from a Greek word which means fire. In the deepest part of the Earth, the minerals are found in a liquid form, which is known as magma. When the magma pushes towards the surface of the Earth, it starts to get cool and converts into the solid Igneous rocks.
The formation of Igneous Rocks:
The Igneous rocks are known as the fire rocks and these are generally formed underground or above the ground. The rocks are formed underground while the magma or the melted rock get trapped in the small pockets of the Earth. As the pockets get cool slowly, the magma turns into the Igneous rocks. Igneous rocks can also be formed when the volcanoes erupt. In this time, the magma rise above the surface of the Earth, When the magma comes above the Earth, it is known as the Lava. After that, the magma or lave spreads on the ground and get cool. This way, the Igneous rocks get formed. All the Igneous rocks do not get cool in the same way, as a result, all these rocks don’t look the same. The rocks can be classified according to the size of the crystals. Some of them cool slowly deep under the surface of the Earth. This way the Intrusive Igneous rocks are formed. The intrusive Igneous rocks are made of large crystals. Granite is an example of this kind of Igneous rock.
Another kind of Igneous rock forms when the erupted lava reaches to the surface of the Earth through the cracks of the Earth. The lava cools very quickly and the rocks formed this way are made with small crystals. These rocks are known as the Extrusive Igneous rocks. Basalt is an example of this kind of Igneous rock.
Obsidian is another kind of extrusive Igneous rocks which gets cooled so fast that it has no crystals and looks like black and shiny glass.
Common features of the Igneous rocks:
• The Igneous rocks are generally classified by the composition and the texture.
• These type of rocks do not contain any fossil.
• The Igneous rocks commonly have no layers in them
• These kind of rocks react with the acid.
• The Igneous rocks can be of both dark and light colored
• These rocks are usually made of two or more than two types of minerals.
• Sometimes glass fibers or openings can be seen in these types of rocks
• The Igneous rocks are commonly made of the mineral crystals of various sizes
• The rocks can also be glassy or fine grained (in case of Extrusive Igneous rocks)