Igneous rocks - Info sheet

Igneous rocks are one of the three main categories of rocks that are classified by their formation process. These rocks originate from magma that has cooled and solidified, and they can be formed either on the Earth's surface or beneath it. When magma erupts onto the surface and then cools, it creates what are known as extrusive igneous rocks. These rocks often have a glassy texture due to the rapid cooling process. Obsidian, a naturally occurring volcanic glass, is a prime example of an extrusive igneous rock. Pumice, on the other hand, has a very different, non-glassy texture and is notable for its use in everyday products like toothpaste and cosmetic items.

In contrast, intrusive igneous rocks are formed from magma that cools and hardens underground. The slower cooling process allows crystals to form, giving these rocks a grainy texture. Granite is a well-recognised type of intrusive igneous rock, renowned for its durability and beauty, making it a popular choice for gravestones, statues, and kitchen countertops. In addition to igneous rocks, the Earth's crust is composed of sedimentary and metamorphic rocks, each with their unique formation processes and characteristics that distinguish them from one another.