Cooled magma forms igneous rocks. These rocks either
crystallize or freeze, resulting two types of igneous rocks – extrusive igneous
rocks and intrusive igneous rocks. Extrusive or volcanic igneous rocks result
from a magma that melted quickly above the earth’s surface or near the earth’s
surface. Crystals may form but needs to be magnified to be seen by the naked
eye. Example of this type of rocks includes obsidian, basalt and pumice.
Intrusive or plutonic igneous rocks are formed from magma that cooled
underground or below the Earth’s surface. Because these rocks slowly-cooled,
large crystals are formed which is visible to the naked eye. Examples of this
type of rocks are diorite, granite and peridotite.
