Summary
The solid part of the Earth is made of rocks, and rocks are made of minerals. A mineral is a natural, solid substance with a fixed composition, like quartz, gypsum or salt; a rock is a mixture of one or several minerals, like granite or limestone.
By how they form, there are three main types of rock. Igneous rocks form when magma cools (granite, basalt). Sedimentary rocks form by the build-up of debris that compacts over time (sandstone, limestone). And metamorphic rocks form when another rock changes through heat and pressure inside the Earth (marble, slate). Over time, some rocks turn into others: this is the rock cycle.
Key points
- Rocks form the solid part of the Earth; they are made of minerals.
- A mineral is natural, solid and of fixed composition (quartz, salt, gypsum).
- A rock is a mixture of one or several minerals (granite, limestone).
- Igneous: form when magma cools (granite, basalt).
- Sedimentary: by build-up and compaction of debris (sandstone, limestone).
- Metamorphic: through heat and pressure (marble, slate).
- Rocks turn into one another: the rock cycle.