Rocks found on the Earth's surface actually come from inside the Earth - so they tell us a lot about the Earth's interior. They are classified (organised) into three main groups: igneous rocks, sedimentary rocks and metamorphic rocks.
Rock types
| Type of rock | Example |
|---|---|
| Igneous rock |
|
| Sedimentary rock |
|
| Metamorphic rock |
Igneous rock
Igneous rocks are formed by magma from the molten interior of the Earth. When magma erupts it cools to form volcanic landforms. If magma cools inside the Earth it forms intrusive rock, which may later be exposed by erosion and weathering. Examples of igneous rocks include basalt and granite.
Example of igneous rocks
| Type of rock | Example |
|---|---|
| Basalt |
|
| Granite |
Metamorphic rock
Metamorphic rocks have been subjected to tremendous heat and/or pressure, causing them to change into another type of rock. They are usually resistant to weathering and erosion and are therefore very hard-wearing. Examples of metamorphic rocks include marble, which originates from limestone,slate, which originates from clay, and schists formed from sandstone or shale (sedimentary rocks).
Slate Quarry, Cullipool
Sedimentary rock
Sedimentary rocks are formed from sediments that have settled at the bottom of a lake, sea or ocean, and have been compressed over millions of years. The sediment comes from eroded rocks carried there by rivers or ice, and from the skeletons of sea creatures. Examples of sedimentary rocks include sandstone, limestone, chalk and clay.
Limestone pavement on top of Malham Cove