Igneous rock is one of the three main rock types based on the method of its formation. It is also referred to as plutonic or volcanic rock depending on where it formed. In a nutshell, to be classified as igneous, a rock must have crystallized and solidified from molten rock (magma) either below ground (intrusive igneous rock) or at or near the surface (extrusive igneous rock).
One of the many way's it can be formed-

1.When a Earthquake is in its full form,if one of the heavier tectonic plates falls under the lighter plate,the heavier one will melt and will become into lava or magma.After this procedure there will be a little crack in between the plates so molten lava will rush out from the pressure.If the plate is under the sea,then solidification will take place and igneous rock will be fromed.

The oldest type of all rocks is the igneous rock (IG nee us). The word "igneous" comes from a Greek word for fire. Deep inside the earth, the temperature is very high and the minerals there are in liquid form called magma. As the magma pushes towards the earth's surface, it starts to cool and turns into solid igneous rock.

All igneous rocks do not cool the same way. That is why they do not look all the same. Some cool slowly, deep under the earth's surface. These are called intrusive igneous rocks. The slow cooling formed rocks with large crystals. Granite is an example of a rock that cooled slowly and has large crystals.

Other rocks formed when the magma erupted from a volcano or reached the earth's surface through long cracks. Magma is called lava when it reaches the earth's surface. Lava cools quickly and forms rocks with small crystals. They are called extrusive igneous rocks. Basalt is an example of this type of rock. Obsidian is an example of another extrusive igneous rock ...more