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.


Igneous Rock

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:

  • Granite
  • Lava
  • Obsidian
  • Pumice
  • Basalt

Sedimentary Rock

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:

  • Sandstone
  • Limestone
  • Flint 
  • Mudstone (shale)
  • Clay
  • Conglomerate
  • Breccia
  • Gypsum

Metamorphic Rock

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:

  • Marble
  • Slate
  • Schists


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

View other relevant My Learning resources or see the teachers' notes page for discussion and activity ideas. 

Scroll down for a list of links and resources on this topic.

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