Igneous rock is formed when magma, molten rock from below
the earth's surface, or lava, molten rock that has emerged from below the surface,
hardens into a solid state. There are many different kinds of igneous rocks, depending
upon where they harden and what materials are contained in them. Igneous rocks form
Earth's crust.
Granite is a type of igneous rock. Granite
is formed when magma is trapped and cooled within a crack or other opening in
pre-existing rock below the surface. Because it cools and hardens slowly, granite has a
coarse texture and individual pieces of material can be seen within the
rock.
Cooling occurs much more quickly when lava reaches
the Earth's surface. As a result, igneous rocks that form on the surface have smoother
textures and much finer material. An example of an igneous rock that cooled on the
surface is obsidian.
See the link below for more
information about how types of igneous rocks are identified and
classified.
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