Hello. Unfortunately, you did not present the experiment to which this question refers, which makes it impossible to answer it exactly, but I will try to help you in the best possible way.
An independent variable is one that occurs without having to be influenced by another variable or element of the experiment, on the contrary, the independent variable has the power to influence and cause changes in other elements.
Regarding the rock cycle, we can consider the following steps:
Magma: it is the initial stage of the rock and is found in the interior of the earth. When it is expelled and comes into contact with the surface undergoing a cooling process
Crystallization: As the magma cools, its composition begins to crystallize until it is completely solid and gives rise to magmatic rock.
Erosion: promotes the wear of this rock through elements such as water, wind, temperature, pressure, climate, weather, among others.
Sedimentation: after the erosion of the magmatic rock, its sediments accumulate forming the sedimentary rocks.
Metamorphism: As more sediments are accumulated, the sedimentary rocks are buried, where they are exposed to high temperature and pressure that start to mold them generating the metamorphic rocks.
Fusion: The temperature and pressure continue to act on the metamorphic rocks allowing them to merge with the magma and turn back to magmatic rock.