Extrusive Igneous Rocks — Reading Comprehension

Deep inside the Earth, rocks can melt into hot liquid called magma. When magma rises and erupts from a volcano, it flows out as lava. When the lava cools and hardens on Earth’s surface, it forms a special type of rock called an extrusive igneous rock.

The word extrusive means “pushed out.” Since these rocks form outside the Earth, they cool much faster than rocks that stay underground. Because of this quick cooling, extrusive igneous rocks often have small crystals or no crystals at all.

One common example is basalt, a dark rock that makes up much of the ocean floor. Another is obsidian, which looks like shiny black glass. You might also know pumice, a light gray rock full of tiny holes. Pumice is so light that it can actually float on water!

Extrusive igneous rocks remind us that our planet is always changing. Volcanoes continue to shape the land, creating new rocks that tell the story of Earth’s fiery past.

Scientists study extrusive igneous rocks to learn about Earth’s volcanoes and the history of its surface. By examining these rocks, geologists can discover how hot the lava was, how fast it cooled, and even what gases were trapped inside.

Fun Fact: The giant island of Hawaii is made mostly of basalt from many volcanic eruptions over millions of years!

What forms extrusive igneous rocks?

What does extrusive mean?

Why do crystals in these rocks stay small?

Which rock looks like black glass?

Why can pumice float?

What do scientists learn from these rocks?

Where is much basalt found?

What makes up Hawaii’s islands?