Which statement best defines metamorphic rock?

• A. Rock changed in structure by heat, moisture, and pressure
• B. Rock formed by the solidification of molten magma
• C. Rock formed by precipitation from mineral-rich solutions
• D. Rock formed when sediments are compacted and cemented together

Answer: (A)

Metamorphic rocks form when existing rocks are transformed by high heat, pressure, and often chemically active fluids, all while staying in a solid state. The statement captures this idea: rocks are changed in structure by heat, moisture, and pressure, which rearranges minerals and can create new textures without melting the rock. That’s what metamorphism does—minerals recrystallize or new minerals form under those conditions, producing features like foliation in some rocks and different mineral makeup.

This differs from other rock types: rocks formed from cooling and solidifying molten magma become igneous rocks; rocks formed by precipitation from mineral-rich solutions become chemical sedimentary rocks; and rocks formed from sediments compacted and cemented together become sedimentary rocks.