When magma cools and hardens beneath the surface or as the result of a volcanic eruption, igneous rock forms. The word igneous actually means "fire" in latin. That's probably the reason why people often think of volcanic eruptions when igneous rock is mentioned! There are two types of Igneous rock, Intrusive Igneous Rocks, and Extrusive Igneous Rocks.
When magma that is deep in the Earth hardens in it's chambers, it forms Intrusive Igneous Rocks. |  |
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Granite is a light colored, course-grained Intrusive Igneous Rock. It constists mainly of Quartz and Felspar. |
When magma erupts onto earth's surface as lava, it then cools and forms Extrusive Igneous Rock. Basalt is a very common Extrusive Igneous Rock. It is a black and white rock with fine-grains due to the rapid cooling of lava at the Earth's surface. |  |
