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Igneous rocks are 'formed by fire'; they begin as magma in the interior of the Earth.
Some are formed by lava cooling on the Earth's surface after being thrown out by a volcanic eruption.
For example, basic lava that flows from constructive margins and forms shield volcanoes cools to form basalt rock. This has been eroded into hexagonal blocks at the Giant's Causeway in Northern Ireland.
Others are formed by magma cooling underground after having been intruded into other rocks without reaching the surface. Granite is an example of this type of igneous rock. It is often intruded during the building of fold mountains along destructive plate boundaries.Granite outcrops on the surface after erosion of the rocks above it over millions of years. Today it is exposed in many places in Scotland and forms most of the moorlands of Devon and Cornwall as well as the dramatic cliffs at Land's End.
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