THE ROCK CYCLE
BY EDWARD SALMON - SMITH

Types of rock.
There are three types of rocks. Sedimentary, for example chalk, limestone, sandstone and shale. Igneous, for example basalt and granite. Finally, Metamorphic, for example slate and marble.

What is the rock cycle?
The Earth's rocks do not stay the same forever. They are continually changing because of processes such as weathering and large earth movements. The rocks are gradually recycled over millions of years. This is called the rock cycle.
For example sedimentary rocks can be changed into metamorphic rocks, and these can be weathered and the pieces transported away. These pieces could be deposited in lakes or seas and eventually form new sedimentary rock. Many routes through the rock cycle are possible.

Diagram

Key words from the diagram.
Sedimentation creates layers or rock particles.
Compaction and cementation presses the layers and sticks the particles together. This creates sedimentary rock.
Rocks underground that get heated and put under pressure are changed into metamorphic rock.
Rocks underground that get heated so much they melt turn into magma. Magma is liquid rock. Magma also comes from deeper inside the Earth, from an region called the mantle.
Pressure can force magma out of the ground. This creates a volcano. When the magma cools it turns into solid rock, called extrusive igneous rock.
Magma that cools underground forms solid rock called intrusive igneous rock.
Areas of rock can move slowly