Science
What is Rock?
A rock is a naturally occurring solid made of one or more minerals. Rocks form the solid outer layer of the Earth, and they're grouped into three main types — igneous, sedimentary, and metamorphic — based on how they formed.
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Watch a 2-minute lesson with voice + animation that explains rock.
Key things to understand
- 1A rock is a solid mass of one or more minerals (or, rarely, organic material).
- 2There are three main types: igneous (cooled from molten rock), sedimentary (compacted layers), and metamorphic (changed by heat and pressure).
- 3Rocks make up the Earth's crust — mountains, the sea floor, and the ground beneath you.
- 4Over millions of years, rocks change from one type to another in the rock cycle.
- 5A rock is usually a mixture of minerals, while a mineral is a single pure substance.
Frequently asked questions
- What are the three types of rock?
- Igneous (formed when molten rock cools and hardens), sedimentary (formed from compressed layers of sediment), and metamorphic (formed when existing rock is changed by heat and pressure).
- What's the difference between a rock and a mineral?
- A mineral is a single, naturally occurring substance with a fixed chemical makeup. A rock is a solid usually made of several minerals mixed together.
- How do rocks change over time?
- Through the rock cycle: heat and pressure, melting, cooling, weathering, and compaction slowly turn one type of rock into another over millions of years.