Igneous rock types have formed when molten volcanic rock or magma has cooled down over time. Igneous rock types can be divided into two subcategories depending on where they have formed. These subcategories are intrusive rocks and volcanic rocks.

Dense and sturdy intrusive rocks have formed deep within bedrock over long periods of time. The most common Finnish rock type, granite, is an example of an intrusive rock. It consists of three minerals: quartz, feldspar and mica. Granite can be easily distinguished from its red-gray color.

Although intrusive rocks have formed deep within bedrock, the erosion of the ground layers above them has slowly brought them to the surface. This process has taken place over the course of millennia.

Due to their studriness, intrusive rock types such as granite are often used in buildings, roadsides, gravestones and memorial statues

The formation of volcanic rocks is connected to volcanic activity. When a volcano erupts, the magma contained within it is released to the surface of the Earth. When the magma arrives at the surface, it begins to cool down and solidify. Volcanic rock types are often porous, spongy, lightweight and matte-colored. Although rocks of this type are rare in Finland, the bedrock of Iceland consists entirely of volcanic rock.

The most common type of lava rock is basalt. Pumice stones are lava rocks that are so spongy and light that they can float in water for a short time.