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.