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What is a rock?

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Quick answer

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.

Key things to understand

  1. A rock is a solid mass of one or more minerals (or, rarely, organic material).
  2. There are three main types: igneous (cooled from molten rock), sedimentary (compacted layers), and metamorphic (changed by heat and pressure).
  3. Rocks make up the Earth's crust — mountains, the sea floor, and the ground beneath you.
  4. Over millions of years, rocks change from one type to another in the rock cycle.
  5. A rock is usually a mixture of minerals, while a mineral is a single pure substance.

People also ask

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.

Part of the guide: Nature & Earth: Living Things and Rocks →