Course: Science Subtest I
Lesson: Dynamic Processes of the Earth (Geodynamics)
Topic: Rock Formation I: The Rock Cycle      Page 9 of 20  

Igneous rocks can form on Earth’s surface from lava as well. When magma reaches Earth’s surface and spills on to the ground, it is known as lava. Cooling lava will form igneous rocks with much smaller crystals. Volcanic eruptions typically involve lava as well. The igneous rocks formed as the result of a volcanic eruption are typically glassy or full of holes.

Learn more about the formation of igneous rocks.


Cooling lava forms igneous rocks. Basalt and pumice are two examples of igneous rocks formed from cooling lava. Basalt typically forms where lava seeps out onto the ocean floor at spreading centers. Much of the ocean floors are made of basalt. Pumice is formed when lava erupts violently from a volcano. The holes in the rock are the result of gases escaping rapidly from the cooling lava. Pumice sometimes floats in water.
Sources: Pumice and Basalt

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