Rocks

Sedimentary Rock

Sedimentary rocks are formed when eroded fragments of old rocks and dead organisms settle (usually in seas or rivers) to form a sediment. Over millions of years, layers of sediment build up and are buried one on top of the other. They are compressed, and their weight squeezes out the water. Eventually the pieces of rock in the sediment become bonded together to form sedimentary rocks.

image: photograph of sedimentary rock with layers

Sedimentary Rock

Igneous Rock

Igneous rocks are formed when hot, molten rock (called magma) cools and solidifies. There are two main types of igneous rock, depending on where the magma cooled:
- Intrusive igneous rocks form when the magma comes from deep underground and is forced into the upper layers of the Earth's crust, where it cools slowly.
- Extrusive igneous rocks form when the magma erupts from a volcano and cools quickly on the ground.

image: photograph of an igneous rock with small crystals

Igneous Rock (THINK FIRE)

Metamorphic Rock

Metamorphic rocks are formed when existing igneous or sedimentary rocks are changed by pressure and heat, but without melting. This can happen by contact with cooling igneous rocks, or at the edges of tectonic plates, where very high temperatures and pressures occur as mountains are being formed.

image: photograph of a layer of metamorphic rock

Metamorphic Rock (THINK CHANGE)

Powermediaplus has a movie on the rock cycle

Diagram of magma in earth Limestone with fossils