Types of rock

Rock is a solid mass of minerals that have joined together over time.

Rocks are natural and not man-made.

There are different types of rocks and the type depends on the minerals that they are made from, and how the rock was made.

Because of this, each type of rock has different properties and uses.

Geology is the study of how the Earth is formed and the things that happen to the Earth.

As part of this, geologists study rocks which can tell them about things that have happened to the Earth in the past.

The oldest rocks found on Earth are believed to be over 4 billion years old!

• There are three types of rock; sedimentary, igneous and metamorphic.

• We call the study of rocks, and how they're formed, geology.

• Granite, an igneous rock, makes up most of the continents on Earth.

• We find most of our fossils in sedimentary rock, when animals and plants are buried by mud and sand which then hardens.

• Metamorphic rocks were originally igneous or sedimentary rocks that have been subject to huge pressure or heat, or sometimes both.

• The word metamorphic is from the combination of the Greek words 'meta' and 'morph', which translates as 'change of form'.

• Mauna Loa, Hawaii, USA is the largest active volcano on Earth. It is 4,170 metres tall and makes up over half of the island of Hawaii.

There are three main types of rock that are found on Earth:

Igneous

Igneous rocks are formed from magma or lava.

Metamorphic

A metamorphic rock starts out as one type of rock, but it then changes into another due to intense heat or pressure.

Sedimentary

Sedimentary rocks are made up of tiny broken pieces of rocks, crystals or minerals.

Did you know?

Friedrich Mohs was a scientist who specialised in rocks and minerals.

He created the Mohs scale of mineral hardness which is still used today to help scientists identify different rocks or minerals. Scientists scratch the minerals to find out how hard or soft they are and seeing where they fit into the scale.

Minerals range from soft, such as talc, to hard, such as diamonds. Diamond is the hardest mineral on Earth.

Properties

The three different types of rocks are made in different ways, which means that they all have different properties.

Some might be harder or softer, and some might let water in more than others.

If we are using rocks to build things that will need to last for a long time, such as houses, we need to know whether the rock that we chose to build it from will be suitable for the job and how it will cope with the rain, the wind and the sunshine.

Let's find out more about the properties and uses of types of rocks.

Hard or soft?

Some rocks are harder than others. For example, granite is a very hard rock. This makes it a good material for building as it doesn’t wear away easily.

Marble is another hard rock. It has an attractive texture and colour and it can be cut and polished. Because of this, it is used to make floor tiles and wall tiles. Some statues are made from marble too.

Chalk is a soft rock and wears away easily. This makes it ideal for making chalk sticks to write on blackboards.

Permeable or impermeable?

If a rock is permeable, it means that water can soak into it and if a rock is impermeable it means that the water doesn't soak into the rock, it just runs off the outside.

Some rocks such as sandstone and chalk are permeable.

Sandstone is good for making into patio slabs as rainwater will soak into the patio and won't make puddles on the top. However, sandstone and chalk are not as good for building houses, statues or other structures. Impermeable stones, such as slate, marble or clay are better for these jobs.

Impermeable rock is good for building with as they stop water getting into buildings.

Geology – Geology is the study of how the Earth is formed and the things that happen to the Earth.

Igneous – Rocks that are formed from volcanic magma or lava. Granite, basalt and pumice are types of igneous rock.

Impermeable – Water cannot soak into impermeable rocks, so it runs off the outside. Slate and marble are impermeable rocks.

Magma – Magma is molten (melted) rock that is formed beneath the Earth's surface.

Metamorphic – A rock that starts out as one type, but then changes into another through natural process. Marble, slate and quartzite are types of metamorphic rock.

Minerals – A mineral is a natural substance that comes from the Earth. Minerals are found in rocks, water and food.

Permeable – Water can soak into permeable rocks. Sandstone and chalk are permeable rocks.

Rock – A solid mass of minerals that have joined together naturally over time.

Sedimentary – Rocks that are made up of tiny broken pieces of other rocks, crystals or minerals. Sandstone, chalk, and limestone are examples of sedimentary rocks.