What type of rock is formed when existing rocks are modified by heat, pressure, and chemical processes?

• A. Igneous rock
• B. Metamorphic rock
• C. Sedimentary rock
• D. Volcanic rock

Answer: (B)

Metamorphism is the process by which existing rocks are altered by heat, pressure, and chemically active fluids, changing their mineral makeup and texture to form new metamorphic rocks. This happens deep in the Earth's crust where conditions are intense enough to rearrange minerals but not melt the rock. Examples include slate (from shale) and marble (from limestone). In contrast, igneous rocks form from cooling molten rock, either underground or at the surface; sedimentary rocks form from weathered fragments that are deposited, compacted, and cemented; volcanic rocks are a type of igneous rock produced by lava erupting or magma reaching the surface. So the described modification by heat, pressure, and chemical processes best describes metamorphic rocks.