Extrusive rock

An igneous rock formed when lava cools and solidifies at or near Earth’s surface. Rapid cooling commonly produces fine-grained or glassy textures.

Lava: Molten rock that has reached Earth’s surface. Extrusive rocks form when lava cools and solidifies.
Igneous rock: Rock formed when molten rock cools and solidifies. Extrusive rock is the surface-formed branch of this broad rock family.
Basalt: A dark, fine-grained volcanic rock rich in iron and magnesium. Basalt is a common extrusive rock formed from relatively low-silica lava.
Volcanic ash: Fine particles of rock, minerals, and volcanic glass expelled during an eruption. Compacted or cemented ash can form extrusive pyroclastic rocks.
Intrusive rock: An igneous rock formed when magma cools and solidifies below Earth’s surface. Intrusive rocks generally cool more slowly underground, unlike surface-formed extrusive rocks.
Volcanic glass: Natural glass formed when molten rock cools too quickly for crystals to grow. Extremely rapid cooling can leave extrusive rock with no crystals.
Magma: Molten or partially molten rock beneath Earth’s surface. Magma becomes lava upon reaching the surface, where extrusive rocks form.
Rhyolite: A light-colored, fine-grained volcanic rock rich in silica. Rhyolite represents the silica-rich end of common extrusive rock compositions.
Tuff: A rock formed when volcanic ash and other fine pyroclastic material consolidate. Tuff is a widespread extrusive rock used in building and studied as an eruption deposit.
Hypabyssal rock: An igneous rock formed from magma solidifying at shallow depths within Earth’s crust. Its shallow subsurface setting lies between typical extrusive and deep intrusive formation.

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