What part of the rock cycle process is most closely associated with soil formation? a) compaction b) crystallization c) erosion d) melting

The correct option is C.
The key process of rock cycle include the following: crystallization, erosion and sedimentation and metamorphism. During the erosion and sedimentation stage, the weathering process breaks down rock particles into smaller pieces. These smaller pieces are transported via erosion to other locations, where they form soils. 

Its weathering for those who googled this answer, or erosion

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