Three Main Types of Rocks

kinds of rocksThe heart of the Rocky Mountains are the rocks. Do you know the three main types of rocks that can be found throughout the world?

The Rocky Mountains are full of high peaks, craggy cliffs, and amazing rock formations. All of these different rocks are one of the three main kinds. The three main types of rocks are: sedimentary, igneous, and metamorphic. Here is a little bit of information to help you understand and identify them.

kinds of rock

Sandstone in the form of Corona Arch located in Southern Utah.

Sedimentary Rock

All kinds of rocks on the surface of the earth get broken down into smaller and smaller pieces, called sediment. Sedimentary rock is rock that is made from this sediment.

Sediment tends to accumulate in certain areas, such as river mouths.  Over time, more and more sediment comes together and becomes thicker and thicker.  This presses the individual pieces together and eventually cements them together, forming sedimentary rock.

Characteristics of Sedimentary Rock

Can be sandy or dusty. May contain fossils and may have layers. The minerals are not arranged in any sort of pattern. Look for no pattern in the rock.

kinds of rock

Granite is an igneous rock. Look at the pattern of the minerals in this rock.  Photo via Flickr.

Igneous Rock

This is rock that forms when liquid magma cools off and solidifies. Towards the center of the earth it is super hot with lots of pressure.  This pressure and heat mean that  there is no rock, but just magma.  As the magma moves towards the surface of the earth and farther from the center it cools off. It can become solid on the surface or just below the surface.

Characteristics of Igneous Rock

It may appear heavy or hard/dense. The minerals are generally in a pattern and fit together like a puzzle (this is because the rock forms from magma that was completely melted down and mixed up). Look for a pattern or jigsaw puzzle in the rock.

kinds of rock

A nice metamorphic rock, showing what look like layers. Photo via Flickr.

Metamorphic Rock

Metamorphic rock forms when rock (any kind of rock) is buried deep within the earth and is subject to great pressures and/or intense heat. The heat must be hot, but not so hot to melt it completely into magma (which would create igneous rock).  The heat and pressure melt the rock, changing it into another kind of rock (thus metamorphic rock).

Meta means ‘change’ and morph means ‘form’, so metamorphic means ‘to change form.

Characteristics of Metamorphic Rock

It is sometimes split into layers like stacks of pancakes with different mineral grains running through the rock. Look for bands or layers.

Rock Cycle

From the outside rocks seem to be hard and never changing. In fact, forces such as wind, water, heat, and pressure can change rocks from one kind to another. This process, called the rock cycle, explains how igneous rocks can change into sedimentary rocks and so on. Read all about the rock cycle here.