- Igneous rocks are formed when rock cools and solidifies.
- Over 700 types of igneous rocks have been described. Most of them formed beneath the Earth's surface.
- Extrusive igneous rocks are formed at the Earth's surface because of the partial melting of rocks.
- Igneous rock are classified according to texture, chemical composition, and the geometry of the rock.
- The word "igneous" is derived from the Latin igneus, meaning "of fire".
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