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Igneous Rocks
Igneous rocks are formed when magma cools and solidifies. These rocks can be formed on the surface of the earth or underground. These were the first rocks that formed on the earth. The term igneous has been derived from the Latin words ‘ignis’ that means fire. There are two different types of igneous rocks, intrusive and extrusive. Extrusive igneous rocks are formed when magma rises up to the Earth’s surface and then hardens. Intrusive igneous rocks are formed when the magma cools and hardens below the Earth’s surface. These rocks have coarse grained crystals.
Quick Facts: –
- Approximately 95% of the earth’s crust is made of igneous rock. Many mountains are also made of these rocks.
- There are more than 700 different types of igneous rock. Basalt, granite, pumice, obsidian etc. are some examples.
- Pumice is a type of extrusive igneous rock. It is also used in many products such as cement, toothpaste etc.
- Bodies of intrusive igneous rock which are usually composed of granite are known as Plutons.
- The most common use of igneous rock is in the construction of buildings. Some of them are also used in making jewelery.
- Intrusive rocks are also known as plutonic rocks and extrusive rocks are also known as volcanic rocks.
- The texture of igneous rocks is determined by the speed of cooling.
- Intrusive rocks have their grainy structure because of their slow process of cooling.
- When intrusive rocks form huge bodies such as those found in the core of mountains, they are known as batholiths.
- When lava cools quickly above the ground then Obsidian rocks are formed.
- Pumice and basalt are good examples of extrusive igneous rocks. Basalt is most commonly used in constructing buildings and statues.
