* Where do igneous rocks originate? (where does the material come from) * How are they formed? (cooling differences)
* What are the two categories of igneous rocks?
* What are the distinguishing characteristics between the two categories of rocks?
Igneous rocks form when magma solidifies. The origin of the molten material may be from Plutons rising from the Asthenosphere due to Subduction of plates or from hot spots in the mantle or from the infill of divergent plate boundaries with basaltic magma. Molten material that cools and solidifies underground, like granite, is called intrusive igneous rock. Molten material that solidifies on the surface, like pumice, is called extrusive igneous rock. They are rocks which have solidified from magma. Magma is the term for liquid or melted rock and is usually quite hot. After all, the term igneous comes from the Latin word for "of fire". Most people have seen pictures or video of magma that flows out of a volcano. When magma flows onto the surface of the Earth it is called lava. When the lava cools and forms a rock, that rock is an igneous rock.
There are also rocks that form from magma that do not reach the surface of the Earth. These rocks form in what are often called Plutons and are also types of igneous rocks. These two types of igneous rocks are called extrusive (because it extruded or came out of the Earth) and intrusive (because it intruded and stayed inside the Earth). They are also referred to respectively as volcanic and plutonic. Igneous rock is rock that is formed by cooling lava/magma. The two categories are extrusive and intrusive. Intrusive rock is when the magma hardens and cools inside the earth, beneath the surface. Extrusive igneous is just the opposite, when it cools outside the surface