How the Rock Cycle Works

Updated April 17, 2017

There are three basic types of rocks found in the rock cycle. The first one is sedimentary. This type can be broken down into two categories: detrital and chemical. The difference is that detrital is formed by organic debris, whereas chemical rocks are formed by water-depositing minerals getting into the rock to crystalize it.

The next type of rock is igneous rock. These rocks are formed by molten rock that has cooled down and crystalized, either below or at the Earth's surface.

Metamorphic rock is formed when extreme heat and pressure come together (usually in magma) to alter a rock's minerals, and it changes into something else, hence the name metamorphic.

Breaking It Down

There are five processes in the rock cycle: metamorphism, weathering and erosion, cementation and compaction, melting, and cooling and solidification.

Weathering and erosion typically create sedimentary rocks. Weathering is when water, air and gravity all come together to break the rocks down into smaller particles, or sediments. There are two kinds of weathering: mechanical and chemical. Mechanical occurs when things are broken down by the water, wind, and air to make detrital sedimentary rocks. Chemical weathering occurs when the chemical composition of the rock is altered by water evaporating from the rock and depositing chemical sediment. Weathering only covers the breaking down process. When water, wind, air or gravity transport the sediment, it's known as erosion.

Over time, this erosion process layers the sediment onto itself, and gravity forces the bottom layers to be moved into the Earth. This process is called compaction. When natural glues like silica and calcite are added to the compacted rock, they are cemented together, hence the term cementation.

Building It Up

As the bottom layers of sedimentary rock are moved further into the Earth, they are heated and melt, where they're later transferred out of the ground by volcanic activity. On the way out of the Earth, they heat rock that's buried in the Earth's crust, transforming it into metamorphic rock. Then, it's shot out of the volcano, where it cools and solidifies. This cooled rock is called igneous rock.

The metamorphic rock and igneous rock are weathered down and eroded, when they become sedimentary rock. They are deposited, layered and the cycle starts all over again.

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About the Author

Thomas McNish has been writing since 2005, contributing to and other online publications. He is working toward his Associate of Science in computer information technology from Hillsborough Community College in Tampa, Fla.