Which statement best describes metamorphic rocks?

• A. They arise from the transformation of existing rocks under heat and pressure.
• B. They are formed by the cooling of magma.
• C. They form from deposition of sediments.
• D. They are formed by the evaporation of water.

Answer: (A)

Metamorphic rocks form when a preexisting rock is transformed by high heat and pressure deep in the Earth’s crust, often with chemically active fluids. This causes minerals to recrystallize and reorient, changing the rock’s texture and mineral makeup without melting. The result is a solid rock that can develop features like foliation or banding as minerals align under pressure. This transformation under heat and pressure is the defining process of metamorphism.

For example, shale can become slate, and limestone can become marble, illustrating how the same original material changes form under the right conditions. In contrast, igneous rocks come from the cooling and solidification of magma, sedimentary rocks form from the deposition and lithification of sediments, and evaporite rocks form when water evaporates, leaving behind minerals.