The surface of the Earth, the Earth’s crust, is made up from layers of rock, covered by layers of soil or by water. Rock is classified according to the way in which it was formed many millions of years ago.
Igneous rock is rock that is formed when molten rock cools, hardens and becomes a solid. It is generally very hard and is often used on road surfaces.
Metamorphic rocks are rocks that have been changed into harder rocks by enormous pressure or high temperatures. Examples of metamorphic rocks are slate and some marbles.
Sedimentary rocks are formed during a build up of layers of particles that are then compressed and cemented together by further layers of particles and include coal, sandstone and chalk.