Types of rock: Sedimentary, metamorphic and igneous

In a nutshell

Rocks are solid substances made up of minerals (minerals are chemical compounds); there are three types of rock: sedimentary rock, metamorphic rock and igneous rock. These different rock types have unique properties and are formed under specific conditions.

Sedimentary, metamorphic and igneous rock 

Sedimentary, metamorphic and igneous rocks are formed under different conditions.

Rock Type	Features	Examples	Graphic
Sedimentary	Formed from small particles (sediments) Sediments form layers (sedimentation) Squashing (compaction) and gluing (cementation) of sediments forms sedimentary rock	Sandstone Limestone
Metamorphic	Formed by changing other rocks High heat and pressure underground is the cause of this change This changes the mineral composition	Quartzite Marble
Igneous	Formed by the cooling of magma/lava Made up of crystals Two types - extrusive and intrusive	Granite Basalt

Igneous rock

There are two different types of igneous rock - extrusive and intrusive:

• Extrusive igneous rocks are formed by lava cooling down quickly on the surface; they are made up of small crystals
• Intrusive igneous rocks are formed by magma cooling down slowly underground; they are made up of large crystals
  

Tip: Lava is the term given to magma which rises to the surface of the Earth's crust.