Igneous rock

Definition

Igneous rock forms from the cooling and solidification of molten magma or lava. It is one of the three main types of rocks found on Earth.

5 Must Know Facts For Your Next Test

1. Igneous rocks are classified into two main types: intrusive (plutonic) and extrusive (volcanic).
2. Intrusive igneous rocks form beneath the Earth's surface, leading to larger crystal sizes due to slower cooling rates.
3. Extrusive igneous rocks cool quickly on or near the Earth's surface, resulting in fine-grained or glassy textures.
4. Common examples include granite (intrusive) and basalt (extrusive).
5. The composition of igneous rocks can provide valuable information about the conditions under which they formed and the nature of the source material.

Review Questions

• What distinguishes intrusive from extrusive igneous rocks?
• Name two common examples of igneous rocks and classify them as either intrusive or extrusive.
• How does the cooling rate affect the crystal size in igneous rocks?

Related terms

Magma: Molten rock located beneath the Earth's surface.

Lava: Molten rock that has erupted onto the Earth's surface.

Metamorphic Rock: Rock type that forms from existing rock undergoing transformation through heat, pressure, or chemical processes.