Which statement best defines metamorphic rock?

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 come from existing rocks that are transformed when they are exposed to heat, pressure, and chemically active fluids. This combination causes minerals to recrystallize and reorient, creating new textures and sometimes foliation, all while the rock remains solid rather than melting. That solid-state transformation is what sets metamorphic rocks apart from igneous rocks, which form when molten material cools and solidifies, and from sedimentary rocks, which form by lithification of sediments or by precipitation from mineral-rich solutions. For example, shale can become slate under directed pressure, and limestone can become marble under heat and pressure.