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What is igneous rock?

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Quick answer

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. Igneous rock forms from cooled, solidified molten rock (magma below ground, lava above).

Key things to understand

  1. Igneous rock forms from cooled, solidified molten rock (magma below ground, lava above).
  2. Slow cooling underground makes large crystals (like granite); fast cooling at the surface makes small crystals (like basalt).
  3. The word 'igneous' comes from the Latin for 'fire'.
  4. It's the original source rock — much of the Earth's crust is igneous.
  5. Over time, igneous rock can weather into sediment or be changed into metamorphic rock.

People also ask

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).

Part of the guide: Nature & Earth: Living Things and Rocks →