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A layer of melted rock lies beneath earth's crust. When this melted rock, called magma, cools and hardens, it becomes igneous rock. Sometimes it remains below earth's surface and hardens slowly over hundreds or thousands of years. As it slowly cools, large mineral crystals form within it. The rock that results is called intrusive igneous rock. An example of thins kind of rock is granite, which has a course texture from the large crystals it contains. When melted rock reaches earth's surface, it is called lava. Once above the surface of earth, it cools rapidly. Only small mineral crystals have time to form before it cools. The rocks that form from the cooled lava are called extrusive igneous rocks. One example of extrusive igneous rock is pumice, which is full of tiny holes from the gas bubbles that were in the lava when it hardened. Another example is obsidian, which has a shiny, glass-like texture.
Igneous rock is a type of lava rock, there are two types extrusive igneous rock, and intrusive igneous rock.
by Fire-heart April 12, 2017
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