Which rock type is formed primarily by heat and pressure changing an existing rock?

• A. Igneous
• B. Metamorphic
• C. Sedimentary
• D. Organic

Answer: (B)

Heat and pressure acting on an existing rock can cause metamorphism, transforming it into metamorphic rock. This change happens while the rock stays mostly solid, as minerals recrystallize and realign under the added stress and temperature. The result is new textures and minerals, often with layered or banded appearance called foliation, and sometimes larger, well-formed crystals. This is different from rocks formed by melting and cooling of magma (igneous rocks) or from compacted and cemented sediments at the surface (sedimentary rocks). Organic rocks come from accumulated plant or animal material that lithifies, not from the heat-and-pressure transformation of existing rocks.