Intrusive rock

An igneous rock formed when magma cools and solidifies beneath Earth’s surface. Slow cooling commonly produces crystals large enough to see.

Magma: Molten or partially molten rock beneath Earth’s surface, containing dissolved gases and crystals. Intrusive rocks crystallize from magma trapped below the surface.
Magma chamber: A body of molten or partly molten rock stored within Earth’s crust or mantle. Many intrusive rocks crystallize within magma bodies before later exposure.
Pluton: A body of intrusive igneous rock crystallized from magma below Earth’s surface. The term describes the underground rock bodies that make up intrusive formations.
Extrusive rock: An igneous rock formed when lava cools and solidifies at or near Earth’s surface. Extrusive rocks cool faster at the surface and usually have finer grains.
Igneous rock: Rock formed when molten rock cools and solidifies. Intrusive rock is the underground-formed branch of this broader rock family.
Phaneritic texture: An igneous texture in which mineral grains are large enough to identify with the unaided eye. Slow underground cooling commonly gives intrusive rocks this coarse-grained texture.
Contact metamorphism: Alteration of surrounding rock by heat and fluids from a nearby igneous intrusion. Hot intrusive bodies can transform the rocks that enclose them.
Obsidian: A natural volcanic glass formed when silica-rich lava cools too quickly for crystals to grow. Its glassy texture contrasts with the crystals typical of slowly cooled intrusions.
Crystallization: The formation of solid crystals from a liquid or vapor as atoms arrange into an ordered structure. Minerals crystallize as magma cools inside the crust.
Pegmatite: An exceptionally coarse-grained igneous rock, commonly formed from water-rich residual magma. Pegmatites are an extreme case of crystal growth in intrusive settings.

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