Home > Rocks > Igneous Rocks > Intrusive Igneous Rocks

Intrusive igneous rocks develop below the Earth's surface, or within the Earth.

Characteristics
Intrusive igneous rocks can be identified by their large crystals. Large is a relative term here. Of course, not every crystal will be 17 feet long. For classification purposes, large means at least big enough to be seen by the naked eye. (We do not need a microscope to see the individual crystals.)

How they are formed
Intrusive igneous rocks develop within the Earth from the slow cooling of magma. Magma is molten (hot, melted) rock below the surface of the Earth. This slow cooling allows time for mineral crystals to form within the rock. Some of these rocks form so slowly that their crystals can become quite large. In western Maine, there are intrusive igneous rocks with crystals that are 17 feet long!

Where they are found
These rocks can be found all over the world, but some famous examples are the granites in Yosemite National Park in California.

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