Rocks are classified in three types based on how they are formed.
The rock cycle explains how the different types of rock form.
The three types of rock at Earth’s mantle melt into magma.
Magma that cools and hardens underground forms intrusive igneous rock.
Weathering breaks the rock into sediment. Erosion causes the sediment to move to other locations.
Pressure squeezes the sediment together, forming sedimentary rock.
Heat and pressure change igneous and sedimentary rock into metamorphic rock.
Most of the ocean floor is made of basalt. This igneous rock continues to flow out of Earth from chains of underwater volcanoes known as “mid-ocean ridges.”
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