Igneous rocks form from molten rocks, which are thick, fluid masses of very hot elements and compounds. There are many different types of igneous rocks. However, they were once melted and have since cooled down. The two major factors that influence the creation of igneous rocks are the original rock that was melted and the cooling history of the molten rocks.

 The original rock could be any initial rock. Plate tectonic mechanisms move rocks throughout the crust, so even sedimentary and metamorphic rocks can become melted again in a subduction zone. The different types of rocks melt into different chemical magmas, which then is dependant on how it cools.

Molten rock with different cooling histories and different chemical composition will form different igneous rocks. If magma cooled inside the crust of the Earth, the rocks will have larger minerals and referred to as plutonic or intrusive rocks. Molten rock that flows out onto the surface is called lava. These rocks are called volcanic or extrusive rocks.

Granite boulder reveals where these rocks
were formed.