Which type of rock is formed when existing rocks are changed by heat, pressure, or chemical reactions?

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

Answer: (B)

Metamorphic rock is formed when existing rocks are changed by heat, pressure, or chemical reactions. This happens while the rock stays solid, causing minerals to recrystallize and sometimes form new minerals or textures, like foliation from directional pressure. It’s different from melting and cooling, which creates igneous rocks, and from deposition and cementation of sediments, which creates sedimentary rocks. For example, slate forms from shale under pressure, marble from limestone with heat and fluids, and quartzite from sandstone. Coal is a sedimentary rock formed from plant material, not from the alteration of an existing rock through heat or pressure.