Rock cycle is the cycle in which rocks tend to change from one type to another.
For instance, igneous rocks may change to metamorphic rocks or sedimentary rocks; sedimentary rocks to metamorphic or igneous rocks, etc. It is a relationship in which rocks tend to change from one type of rock to another.
Necessary conditions for rock cycle to take place
First, the molten rocks are erupted from the interior of the earth and then cool and solidify to form igneous rocks.
Secondly, the igneous rocks are subjected to denudation process to form sedimentary rocks.
Third, either igneous or sedimentary rocks undergo metamorphism, due to prolonged heat and pressure, to form metamorphic rocks.
Fourth, metamorphic or igneous rocks can undergo weathering process through erosion and transportation of sediments which are further deposited in layers in the ocean or lake floors where they are cemented and consolidated to form sedimentary rocks and vice versa.
5. Fifth, metamorphic or sedimentary rocks can be subjected to heat and pressure where melting take place and later cooling, due to low temperature, to form igneous rocks.

The rock cycle
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