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The rock cycle starts in magma, however it does not always start here. Rocks either form inside the lava chambers, or outside the volcano, when the lava cools. Then by the process of weathering the rocks break down into smaller sediments. Then it rains and the sediment gets transported to the ocean due to erosion, where it settles on the bottom, and becomes subject to compaction, and changes into sedimentary rock over a long period of time. Then it enters the Mantle of the earth.. Sometimes the rock will form into a metamorphic rock due to heat and pressure, and sometimes the rock totally melts, and gets deposited back into a volcano somewhere on the Earth. Although, what really makes this cycle go 'round is plate tectonics. The plates move and hit each other, and subduction happens, melting rocks and adding to the mantle under the Earth, so more igneous rocks can form.

The Rock Cycle

The rock cycle is  the cycle that explains how the 3 rock types are related to each other and form one type of rock to another over a period of time. The types of rocks that are used in this process are igneous rocks, which are made from volcanoes, sedimentary rocks, which are formed by sediment anywhere on earth, and metamorphic rocks, which are formed by heat and pressure.
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