Horrible Science: Cycle of Rock

What is the rock cycle?

Horrible Science image of different types of talking rocks in a classroom.

The rock cycle is how rocks change from one type of rock to another.

Rocks change between igneous, sedimentary, and metamorphic types.

These changes happen through processes such as melting, cooling, applying heat and pressure, weathering, erosion and cementation.

Watch: Cycle of Rock

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Rock out with Mack Slack and see how different types of rocks are formed and change over time.

How are different rocks formed?

An igneous rock is formed when magma (molten rock that is found below the earth's surface) cools down.

Over time, this igneous rock is broken down into tiny pieces through weathering and erosion.

Weathering is when rocks are broken down into smaller pieces by water, ice, wind, or temperature changes. Erosion is the movement of those broken-down materials from one place to another by natural forces like wind, water, ice, or gravity.

A sedimentary rock is formed when these tiny pieces (called sediment) are then pressed and squashed tightly together.

This rock may become buried deep underground, where it is heated and pressed to become a metamorphic rock.

Eventually, this metamorphic rock might melt again into magma and the cycle begins again.

Explore the main types of rock

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$Obsidian rock - a shiny, black, glass-like rock consisting of sharp, fractured reflective surfaces.$
Image caption,
Igneous rocks
Igneous rocks form when molten (melted) rock, from beneath the Earth’s surface, comes to the surface and solidifies (becomes solid). Granite, obsidian and pumice are examples of igneous rocks. Granite makes up most of the Earth’s continents.
Image caption,
Sedimentary rocks
Sedimentary rocks were once igneous rocks. They form when layers of sediment (tiny rock pieces, sand, shells) are compacted and cemented together. Fossils are mostly found in sedimentary rock. Shale, limestone, and sandstone are examples of sedimentary rocks.
Image caption,
Metamorphic rocks
Metamorphic rocks were once sedimentary or igneous rocks. They form when sedimentary or igneous rocks are exposed to intense heat and pressure deep underground. Slate, marble and anthracite are examples of metamorphic rocks.

Horrible Science fact

It takes millions of years for rocks to form and go through the rock cycle. However, humans are unlikely to ever run out of rock as the rock cycle just keeps on going.

Find out more about the different types of rocks.