Science
What are the three types of rock?
Quick answer
Rocks are natural solids made of minerals. The three types are igneous (cooled melted rock), sedimentary (squashed layers of bits) and metamorphic (changed by heat and pressure).
In one sentence
Rocks are the hard natural material that makes up the Earth's crust, and they come in three main types depending on how they were made.
Explained
Rocks are made of minerals, natural solid substances, a bit like a fruitcake is made of different ingredients. Scientists sort rocks into three groups by how they formed.
Igneous rock forms from melted rock. Deep underground, rock can be so hot it melts into magma. When magma cools slowly underground, it makes rock with big crystals, like granite. When it erupts from volcanoes as lava and cools quickly, it makes rock with tiny crystals, like basalt, or glassy obsidian.
Sedimentary rock forms from bits. Wind, water and ice wear rocks into sand, mud and pebbles, called sediment. Rivers carry it to lakes and seas, where it settles in layers. Over millions of years, the layers get squashed and cemented into rock, like sandstone, limestone and chalk. Sedimentary rocks often contain fossils.
Metamorphic rock is rock that has been changed. Heat and pressure deep underground, for example where mountains are being pushed up, can change one rock into another without melting it. Limestone becomes marble; mudstone becomes slate.
Rocks are slowly recycled in the rock cycle. Any rock can be worn down, melted or squeezed and turned into another type. It happens far too slowly to see in a lifetime.
Examples
| Rock | Type | Uses |
|---|---|---|
| Granite | igneous | kitchen worktops, buildings |
| Basalt | igneous | road stones |
| Sandstone | sedimentary | buildings, walls |
| Chalk | sedimentary | (classroom chalk used to be made from it) |
| Marble | metamorphic | statues, floors |
| Slate | metamorphic | roof tiles |
rock
mountain
volcano
shell
Common mistakes
- "All rocks are the same, just different colours." They form in very different ways, which gives them different properties.
- "Rocks never change." They change all the time, but usually very slowly, over thousands to millions of years.
- "Soil is a type of rock." Soil contains tiny bits of rock mixed with dead plant and animal matter, water and air.
Quick quiz
Rocks
Check what you know with 4 quick questions.
Question 1 of 4
How does igneous rock form?
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Collect a few pebbles and sort them: Are they hard or crumbly? Can you see crystals or layers? Do they soak up water? Then print more science activities.
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Related topics
Fossils
Fossils are the preserved remains or traces of plants and animals that lived long ago, usually found in sedimentary rock. They help scientists learn how life on Earth has changed.
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A volcano is an opening in Earth's crust where hot melted rock, gases and ash escape. Over time the cooled lava and ash can build a mountain.
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A mountain is a very high landform with steep sides and a peak. Most form when tectonic plates push together or when volcanoes build up.
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An electric circuit is a complete loop that electricity flows around. A simple circuit has a battery, wires and a component like a bulb. If the loop is broken, the electricity stops.
Digestive system
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