Which rock is formed by metamorphism of existing rocks due to heat and pressure, without melting?

• A. Marble
• B. Granite
• C. Basalt
• D. Sandstone

Answer: (A)

This item tests understanding of metamorphism in the solid state—how existing rocks are altered by heat and pressure without melting. Marble forms when limestone, a sedimentary rock, is subjected to heat and pressure that cause the calcite minerals to recrystallize, producing a dense, interlocking crystal texture. The rock changes shape and composition while remaining solid, so there’s no melting involved. That solid-state transformation is why marble is classified as a metamorphic rock. In contrast, granite and basalt come from magma that cools and solidifies (igneous), and sandstone forms from cemented sand grains (sedimentary), not through metamorphism.