Igneous rock originates from magma and comes in two types: intrusive rock and extrusive rock. When magma cools below the Earth's surface we call it intrusive rock. This cooling usually takes place slowly, which allows for large crystals to form, as in a granite. When magma ends up on the Earth's surface as a lava and cools, we call this extrusive rock. Cooling at the Earth’s surface occurs rapidly, which only allows for small crystals to grow, such as in a basalt.
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