Which of the following is a nonfoliated metamorphic rock?

• A. Slate
• B. Marble
• C. Gneiss
• D. Schist

Answer: (B)

Metamorphic rocks develop foliation when pressure is applied more in one direction than another, causing minerals to realign into layered or banded textures. If pressure is not directional, or if heat recrystallizes minerals without aligning them, the rock becomes nonfoliated.

Marble forms from limestone through heat and pressure that rearrange calcite grains into a new, interlocking crystalline texture. This process increases size and cohesion of crystals but doesn’t create aligned layers, so marble lacks foliation and is nonfoliated.

Slate, gneiss, and schist all show directional alignment of minerals: slate through fine foliation from low-grade metamorphism, gneiss with distinct mineral-banded layering at high-grade metamorphism, and schist with visible platy minerals aligned to give schistosity.