What is the rock cycle, and how do igneous, sedimentary, and metamorphic rocks transform between each other?

• A. The rock cycle describes transformations among rock types: igneous rocks weather to form sediments, which lithify into sedimentary rocks; burial and metamorphism form metamorphic rocks; rocks can melt to form magma and crystallize into igneous rocks
• B. Igneous rocks never weather to sediments
• C. Sedimentary rocks melt to become metamorphic rocks only
• D. Metamorphic rocks weather to become igneous rocks immediately

Answer: (A)

The rock cycle is the set of processes that connect the three main rock types and explain how they transform from one form to another over time. Igneous rocks form when molten rock crystallizes. When exposed at the surface, they weather and erode into sediments, which are deposited and then lithified into sedimentary rocks. Deep burial and exposure to heat and pressure can alter rocks into metamorphic rocks. If rocks melt, they become magma, and as magma cools and crystallizes, new igneous rocks form. This cycle shows how rocks continually recycle through different forms rather than a one-way path.

Igneous rocks do weather and break down, so the idea that they never weather doesn’t fit. Sedimentary rocks don’t only become metamorphic rocks by melting–they can also melt to form magma and crystallize into igneous rocks, so that narrower claim isn’t complete. Metamorphic rocks don’t transform directly into igneous rocks through immediate weathering; weathering produces sediments, and only melting and crystallization yield igneous rocks, so the rapid metamorphic-to-igneous path isn’t accurate either.