Science
What is Igneous Rock?
Igneous rock is rock that forms when molten rock — magma or lava — cools and hardens. It's one of the three main rock types. Granite (cooled slowly underground) and basalt (cooled quickly at the surface) are common examples.
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Watch a 2-minute lesson with voice + animation that explains igneous rock.
Key things to understand
- 1Igneous rock forms from cooled, solidified molten rock (magma below ground, lava above).
- 2Slow cooling underground makes large crystals (like granite); fast cooling at the surface makes small crystals (like basalt).
- 3The word 'igneous' comes from the Latin for 'fire'.
- 4It's the original source rock — much of the Earth's crust is igneous.
- 5Over time, igneous rock can weather into sediment or be changed into metamorphic rock.
Frequently asked questions
- How does igneous rock form?
- When molten rock cools and solidifies. Magma cooling slowly underground forms coarse-grained rock like granite; lava cooling quickly at the surface forms fine-grained rock like basalt.
- What are examples of igneous rock?
- Granite, basalt, obsidian, and pumice. Granite forms underground; basalt, obsidian, and pumice form from lava at or near the surface.
- Why do some igneous rocks have bigger crystals?
- Cooling speed. Slow cooling deep underground gives crystals time to grow large; fast cooling at the surface freezes them small, sometimes into glass (obsidian).