Have you ever wondered what happens when lava cools? Igneous rock forms, of course. The mantle of the Earth is very hot, but it remains solid because it’s under intense pressure. Sometimes, though, the pressure may ease. When this happens, the mantle melts and becomes magma, or hot, liquid rock. The magma cools slowly over millions of years and forms hard rock, such as granite. Rocks that form from magma are known as intrusive igneous rock because they form beneath the ground.
Sometimes, the hot magma erupts at the Earth’s surface in the form of cracks, fissures or volcanoes. This hot rock is called lava. As the lava cools, it forms extrusive, igneous rock, such as basalt or pumice. Most igneous rocks are very hard because they were created under intense pressure and heat. Pumice is a soft, light rock that has many holes.
Fun Facts About Igneous Rocks for Kids
- The ocean floor is usually made of basalt rock, a hard, black, extrusive rock. Lava fields in Hawaii cool to form basalt rock.
- Rhyolite is similar to granite but it comes from volcanic lava. It is lighter in weight than granite, which is very dense.
- Sometimes igneous intrusions form underground in huge masses, known as batholiths. These batholiths can be 60 miles across.
- The Giant’s Causeway was made from a lava flow that erupted about 55 million years ago. As the lava cooled, it split and formed about 40,000 basalt pillars. The pillars look like huge stepping stones.
Igneous Rocks Vocabulary
- Igneous: made from molten rock (from the Greek word for fire)
- Mantle: the section of the Earth lying beneath the crust
- Magma: liquid rock beneath the Earth’s surface
- Lava: liquid rock that spews onto or near the surface of the Earth
- Intrusion: rock that forms under the ground
- Extrusion: rock that forms on or near the Earth’s surface
All About Igneous Rocks Video for Kids
This is the best video we found for kids to learn about the Igneous Rock:
Igneous Rocks Q&A
Question: Are igneous rocks useful?
Answer: People use igneous rocks in many ways. Granite counter tops are just one way. Obsidian, which is a very sharp, glass-like volcanic rock was used for tools or arrowheads.
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