List of rock types facts for kids

Rocks are amazing! They are natural solid materials made of one or more minerals. Geologists, who are scientists who study the Earth, group rocks into three main types based on how they are formed. These types are igneous rock, metamorphic rock, and sedimentary rock. There are many different kinds of rocks within these main groups. Each rock type has its own unique mix of chemicals, minerals, and textures.

Igneous Rocks

A sample of andesite rock. It has small holes filled with minerals.

Igneous rocks are formed from melted rock that has cooled down and become solid. This melted rock is called magma when it's deep inside the Earth. When magma erupts onto the Earth's surface, it's called lava.

Here are some examples of igneous rocks:

• Andesite
• Basalt – This is a common dark rock.
  • ʻAʻā – A type of basaltic lava that looks rough and crumbly.
  • Pāhoehoe – A type of basaltic lava that looks smooth and ropy.
• Diorite
• Gabbro
• Granite – A very common rock often used in buildings.
• Obsidian – This is a natural volcanic glass.
• Pumice – A very light rock with lots of holes, formed from volcanic eruptions. It can even float on water!
• Rhyolite
• Scoria – A dark, bubbly volcanic rock.
• Syenite
• Tuff – A rock made from volcanic ash.

Sedimentary Rocks

A layer of bituminous coal in West Virginia.

Layers of limestone and shale rocks.

Dolomite crystals from Morocco.

Turbidite rock from South Italy.

Sedimentary rocks are formed from pieces of other rocks, minerals, or even living things. These pieces, called sediment, are carried by wind or water. Over a long time, layers of sediment build up and get pressed together. The weight of the layers above squeezes out water and air. Minerals then act like glue, cementing the particles together.

Here are some examples of sedimentary rocks:

• Arkose
• Breccia – A rock made of sharp, angular pieces of other rocks.
• Chalk – A soft, white limestone.
• Chert
• Claystone
• Coal – A black rock formed from ancient plants. We burn it for energy.
• Conglomerate – A rock made of rounded pebbles and stones.
• Dolostone
• Flint – A hard type of chert.
• Limestone – A common rock often made from the shells of sea creatures.
• Mudstone
• Sandstone – A rock made from grains of sand.
• Shale – A soft rock that splits easily into thin layers.
• Siltstone
• Travertine
• Turbidite

Metamorphic Rocks

Phyllite rock.

Banded gneiss with a granite dike.

Marble rock.

Quartzite rock.

Manhattan Schist from New York.

Slate rock.

Metamorphic rocks are formed when existing rocks are changed by intense heat, pressure, or chemical reactions. This often happens deep inside the Earth where temperatures and pressures are very high. The original rock changes its minerals and texture to become a new type of rock.

Here are some examples of metamorphic rocks:

• Anthracite – A hard, shiny type of coal.
• Gneiss – A rock with distinct bands of different minerals.
• Granulite
• Hornfels
• Marble – This rock forms from limestone. It's often used in statues and buildings.
• Migmatite
• Mylonite – A rock formed by strong squeezing and grinding.
• Phyllite – A rock with a wavy, shiny surface.
• Quartzite – This rock forms from sandstone. It is very hard.
• Schist – A rock that can split into layers. It often has visible flakes of minerals.
• Serpentinite
• Slate – This rock forms from shale or siltstone. It splits easily into thin, flat sheets and is used for roofing and blackboards.
• Soapstone – A soft rock that feels like soap.

See also

• List of minerals
• Rock cycle – Learn how rocks change from one type to another.