Rocks are classified into three main groups: igneous rocks, sedimentary rocks and metamorphic rocks. This classification is based on how they were formed and their characteristics.
Igneous rocks are formed by magma from the molten interior of the Earth. Whenmagma erupts it cools to form volcanic landforms. When it cools inside the Earth it forms intrusive rock, which may later be exposed by erosion and weathering. Intrusive rock will have large crystals as it has cooled slowly. Magma that has cooled on the surface is known as extrusive rock. This will have small crystals as it has cooled quickly.
Examples of igneous rocks include basalt and granite.
A river carries, or transports, pieces of broken rock as it flows along. When the river reaches a lake or the sea, its load of transported rocks settles to the bottom. We say that the rocks are deposited. The deposited rocks build up…