Properties of Extrusive Igneous Rocks — Reading Comprehension

When a volcano erupts, lava flows onto Earth’s surface. As this lava cools and hardens, it forms extrusive igneous rocks. These rocks have special properties that tell us about how they were formed.

One important property is texture. Because lava cools quickly above ground, the crystals in extrusive rocks are usually very small. Some rocks may even look like glass because crystals had no time to form.

Another property is color. Many extrusive igneous rocks, like basalt, are dark. Others, like rhyolite, may be lighter. Color often depends on the minerals inside the rock.

Some extrusive rocks, such as pumice, are full of holes. These holes form when gas bubbles are trapped in the lava as it cools. Pumice is so light it can float on water! Another example is obsidian, which is smooth and shiny, almost like black glass.

Extrusive igneous rocks are also very hard and durable. That means they do not break easily and can last for millions of years. This is why basalt is often used in construction.
By studying these properties, scientists can learn about past eruptions and how our planet’s surface has changed over time. 

Fun Fact: The giant statues on Easter Island were carved from volcanic tuff, a type of extrusive igneous rock!

Why are crystals small in extrusive rocks?

What makes pumice full of holes?

Which rock is shiny and glassy?

What property makes basalt useful?

What affects rock color?

What does texture tell scientists?

What were Easter Island statues carved from?

Which rock can float on water?