Igneous Rocks
Science: KS3, topic 2.5.3
Igneous Rocks
Igneous rocks are formed from cooling magma. Igneous rocks can either be formed inside the Earth’s crust or outside.
Igneous rocks
- Igneous rocks are formed from cooling magma.
- There are two types of igneous rock: intrusive and extrusive.
Features of igneous rock
- Igneous rocks are very hard.
- Igneous rocks contain crystals.
Intrusive igneous rock formation
- Intrusive igneous rocks form inside the Earth’s crust.
- Intrusive igneous rocks form from magma.
Intrusive rock cooling
- Intrusive igneous rocks form underground where it is hotter.
- So intrusive igneous rocks take a long time to cool.
- Taking a long time to cool means the crystals that form are larger.
Extrusive igneous rock formation
- Extrusive igneous rocks form outside the Earth’s crust.
- Extrusive igneous rocks form from lava from a volcanic eruption.
Extrusive rock cooling
- Extrusive igneous rocks form on the Earth’s surface where it is cooler.
- So extrusive igneous rocks take a short time to cool.
- Short cooling time means the crystals that form are smaller.
Examples and their uses
- Granite
- Granite is used in building and tiles.
- Basalt
- Basalt is used in construction and building roads.
Pumice uses
- Pumice
- Pumice floats on water because of air that was trapped when it cooled.
- Some people use pumice to remove the dead skin from their feet.
Obsidian uses
- Obsidian
- Obsidian is jet black in colour.
- Obsidian has been used for making tools and weapons such as arrowheads.
Test yourself on Igneous Rocks
Why do intrusive igneous rocks have larger crystals than extrusive igneous rocks?
Extrusive Igneous Rocks
Intrusive Igneous Rock
What are the two categories of igneous rocks?
Select the correct statement in each pair