Hot Rocks = Igneous Rocks
How do igneous rocks form?
Igneous rocks are volcano rocks - rocks made from the liquid magma that comes out of volcanoes. When the magma cools, igneous rocks are made. All of the rocks on Earth start out as igneous rocks.
The crystal size of the igneous rock depends on where the magma is when it cools down. If the magma is deep within the Earth’s crust, it can take thousands of years to cool down enough to turn into a solid rock. When it takes a long time to cool down, the crystals in the rock are bigger.
Sometimes the magma is spewed out from a volcano. When the magma reaches Earth's surface, it is called lava. When this happens, because it is at the surface of the Earth, the lava can cool to solid rock in a matter of hours. The crystals in the rock are small and sometimes even too small to see!
So there are two categories of igneous rocks:
- Intrusive, which form INside the Earth and have large crystals because they cool slowly
- Extrusive, which EXit the earth and have small crystals because they cool quickly
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Igneous rock examples
How are igneous rocks used?
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