Rocks at Cliffe Castle Museum
Types of Rock
What is a rock?
A rock is a mixture of different minerals bonded together in a lump. We usually describe and classify rocks by how they are formed.
Imagine igneous rock as a hot-headed person whose temper can boil up, but will eventually cool down. Igneous rocks are formed when very hot liquid rock (magma) slowly cools down.
This can happen slowly inside the Earth or more quickly after the magma reaches the surface. This can happen when a volcano erupts and a mixture of hot gas, ash and rock travels down its sides.
Examples of igneous rocks include:
Particles (tiny pieces) of gravel, sand, mud, silt, dead animals and plants are constantly moving into stretches of water and being deposited there. They form something called the 'sediment', which is the mud at the bottom of a lake and the sand under the sea.
After many thousands of years, the sediment is tightly compacted and cemented together, until it is so hard that it forms sedimentary rock. Fossils are often found in sedimentary rock.
Examples of sedimentary rocks include:
- Mudstone (shale)
If any type of rock travels deep inside the Earth, after a little time the vast amounts of pressure and heat beneath the Earth's surface will change it into a metamorphic rock.
Examples of metamorphic rocks include:
Compacted - when something is closely packed together
Constantly - happening again and again
Deposit - when something is left or dropped somewhere
Fossils - remains of animals or plants preserved inside rock or another long-lasting natural material
Magma - hot, liquid rock under the surface of the Earth, which comes out when a volcano erupts
Outcome - the result of something
Particles - very small pieces of something
Vast - so big it is hard to measure