Which rock type is formed from an existing rock changed by heat, pressure, or chemical reactions?

• A. Rock cycle
• B. Sedimentary rock
• C. Igneous rock
• D. Metamorphic rock

Answer: (D)

Metamorphic rocks form when an existing rock is altered by heat, pressure, or chemically active fluids deep in the Earth's crust. These conditions cause minerals to recrystallize and realign, changing the rock’s texture and sometimes its mineral composition without it melting. That’s why you can get foliated rocks like slate or schist when pressure is directed, or non-foliated rocks like marble when heat and fluids drive chemical changes. Common transformations include shale turning into slate, limestone into marble, and sandstone into quartzite. This distinguishes metamorphic rocks from igneous rocks (formed by cooling of molten material) and sedimentary rocks (formed by deposition and lithification of sediments). The scenario described points to metamorphic rock.