What Is An Igneous Rock？

Are you looking for an easy way to teach your child about rocks and minerals? We’ve put together a set of free materials that parents and teachers can use right away. In this lesson, your child will dive into the fascinating world of igneous rocks.

We’ll explore the rocks formed from cooled magma, divided into two main types. Explore science in a more engaging way with captivating 3D videos and interactive quizzes. Download our app to get started!

What you will learn from this lesson

How are Igneous Rocks Formed?

Igneous rocks, also known as fire rocks, are one of the three main rock types, alongside sedimentary and metamorphic rocks. What is an igneous rock? It’s a rock that forms when magma or lava cools down and solidifies. Magma, the source of igneous rocks, is hot material constantly moving in the upper part of the Earth’s mantle layer, beneath the crust.

What are the Two Main Types?

Igneous rocks are classified into two main groups based on where they cool: intrusive and extrusive rocks.

• Intrusive rocks form when magma gets trapped inside the Earth’s crust and cools down very slowly. This slow cooling process allows enough time for the tiny minerals inside the magma to grow and become clearly visible. Granite is a common example of an intrusive rock.
• Extrusive rocks form when magma erupts and flows out onto the Earth’s surface as lava, where it cools quickly.

What Makes Extrusive Rocks Different?

Because extrusive rocks cool so quickly on the surface, their minerals don’t have enough time to grow large. Therefore, extrusive rocks often have very small minerals or even none at all. This is a key difference from intrusive rocks like granite.

Examples of extrusive rocks include:

• Basalt, a typical extrusive rock that forms when surface magma cools quickly.
• Pele’s hair, which forms when rapidly shot-out lava is stretched into fine threads before it cools quickly.
• Pumice, which forms when magma from underwater volcanoes rapidly cools upon contact with water, trapping gases to create lots of vesicles, or small holes. This high amount of trapped gas and vesicles makes pumice so light that it can float on water.

Fun Fact

• Pumice is an extrusive rock that can actually float on water because it’s so light.
• Pele’s hair is a type of extrusive rock that is made of fine threads of lava stretched in the air.
• Basalt forms from surface magma that cools very quickly before its minerals can grow larger.

Vocabulary

• Igneous Rocks: Rocks formed when magma or lava cools down and solidifies.
• Magma: Scorching hot material constantly moving in the upper part of the Earth’s mantle layer. Magma is the source material for all igneous rocks.
• Lava: Magma that flows out of a volcano onto the Earth’s surface after an eruption.
• Crust: The outermost layer of the Earth, made up of solid rocks and having uneven thickness.
• Mantle: The layer of the Earth beneath the crust where magma moves in the upper part.
• Core: The innermost of the Earth’s three main layers.
• Intrusive Rocks: A family of igneous rocks formed when magma is trapped and cools down slowly inside the Earth’s crust. This slow cooling allows time for large, clearly visible minerals to form.
• Extrusive Rocks: A family of igneous rocks formed when magma erupts onto the surface and cools quickly. They have very small minerals or none at all because of the rapid cooling.
• Granite: A type of intrusive rock that cools slowly inside the Earth’s crust, leading to large, obvious mineral growth.
• Basalt: A typical extrusive rock that forms from magma quickly cooling after reaching the surface, resulting in very small minerals.