Answer and Explanation:
Igneous rocks form most of the earth´s crust. They are the result of the solidification of rocky, molten material, the magma. Rocks are melt in the interior of the earth´s crust or in the mantle, and then, as they are less dense than the other rocks, tend to ascend toward the surface. As they ascend, they get cold and solidify.
There are two kinds of igneous rocks, according to the moment of solidification. Extrusive igneous rocks are the ones formed when the molted material gets to get to the earth´s surface and crystalize there. Intrusive rocks get formed when the magma loses its motility before reaching the surface, ending by crystalizing in the deepness.