Igneous rocks are formed by solidification of cooled magma (molten rock) either below (plutonic) or above (volcanic) the surface of the earth.
The magma consists of partial melting of pre-existing rock and can be caused by one or a combination of; an increase in temperature, pressure changes, change in composition.
Volcanoes are a sign that our planet is immensely hot inside.
An example of an igneous rock is granite. The name comes from the Latin word meaning 'fire'. This is a clue – the rocks were originally very hot! But then they cooled down slowly into a solid rock made up of different bits stuck together called crystals. They are often very beautiful and sparkle in the sunlight.