Yet the fact that rocks can change in different ways is one aspect of the rock cycle that sets it apart from other cycles.
Here we will highlight the three main rock types, their formation, and their common engineering uses, if any.
How many types of rocks are there on Earth?
There are three main types of rock involved in the rock cycle: igneous, sedimentary and metamorphic.
What are igneous rocks?
Magma, which is molten rock, is the origin of igneous rocks (from the Latin ignis, meaning “fire”). When igneous rocks form deep underground, they are called intrusive or plutonic igneous rocks. If they form above the earth’s crust, they are called extrusive or volcanic igneous rocks.
They are generally difficult to break because they are mostly crystalline (made up of interlocking crystals).
Lava is the term used to describe magma that rises to the earth’s crust and erupts from volcanoes on the surface (i.e. no longer underground). These molten materials eventually cool, harden, and can crystallize to form minerals. Igneous rocks are the solid byproducts of magma, lava, or volcanic activity.
Intrusive igneous rocks have a coarse texture and large mineral grains, formed over thousands or millions of years, slowly cooling inside the Earth. In contrast, extrusive igneous rocks have very small grains and a relatively fine texture because the magma cools faster on the surface, giving crystals less time to form.
It is important to note that igneous rocks are not only formed from mantle materials. Any type of rock buried deep in the lithosphere can come into contact with magma, causing the composition of molten rock to change to igneous rock.
Types of igneous rocks
Basalt, an extrusive igneous rock, includes tightly packed crystals (about 1 mm in size). Vesicles – bubbles of gas that were captured as lava cooled – are frequently found in this igneous rock. Small pieces of basalt are typically used as a railway “ballast” which serves as resistance to heavy loads and drainage.