What term describes rocks altered by heat and pressure?

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

Answer: (B)

Rocks altered by heat and pressure are metamorphic rocks. This happens when existing rocks are subjected to higher temperatures and pressures deep in the Earth's crust, causing minerals to recrystallize and align into new textures, often producing foliation. Heat lets minerals rearrange without melting, while pressure shapes the minerals and strengthens their alignment, giving rocks such as slate, phyllite, schist, and gneiss their characteristic forms. If melting occurs, the rock becomes igneous instead of metamorphic. Sedimentary rocks form mainly from the accumulation and lithification of sediments, and clastic refers to a texture of sedimentary rocks made from fragments, not to metamorphism. So the term for rocks altered by heat and pressure is metamorphic.