When magma cools off earth's surface, which type of crystalline structure is usually found?

When magma cools off Earth's surface, the type of crystalline structure that is usually formed is extrusive igneous rocks. The hot lava is exposed to the cool air and water, this makes it cool down at a very rapid rate. The rocks formed by the top surface of the magma cools fast enough to not form large rocks. I hope it helps you. 

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