Question

Read the passage carefully and answer the following questions.

The lava solidifies after coming out on the Earth’s crust during volcanic eruptions. The process of cooling and formation of crystals in the lava is fast and sudden. The crystals formed are small and smooth. The rocks thus formed are called the extrusive igneous rocks, lava rocks or the volcanic rocks. These lava rocks may form the volcanic mountains, volcanic plateaus or lava flow. The most common examples of such rocks is Basalt. Other examples are Gabbro and Obsidian. Extrusive igneous rocks can also have a vesicular, or “holey” texture. This happens when the ejected magma still has gases inside of it so when it cools, the gas bubbles are trapped and end up giving the rock a bubbly texture. Pumice rock is a classic example.

1. Why do the extrusive igneous rocks have small and smooth crystals?
2. Which is the most common type of rock formed from the cooling down of lava?
3. Why does the pumice rock have bubbly texture?

Answer 1

1. Extrusive igneous rocks have small and smooth crystals because the process of cooling and formation of crystals in the lava is fast and sudden after it comes out on the Earth’s crust during volcanic eruptions. This rapid cooling does not allow large crystals to form, resulting in small and smooth crystals.
2. The most common type of rock formed from the cooling down of lava is Basalt.
3. Pumice rock has a bubbly texture because when the ejected magma still has gases inside it and cools rapidly, the gas bubbles get trapped inside the rock. This trapped gas creates a vesicular or “holey” texture, giving the rock a bubbly appearance.