Which statement best describes foliated metamorphic rocks?

• A. They have planar layering due to aligned minerals.
• B. They are formed by rapid cooling of lava on the surface.
• C. They lack any preferred orientation of minerals.
• D. They originate from the cementation of sediments.

Answer: (A)

Planar layering formed by alignment of minerals is what defines foliated metamorphic rocks. Under directed pressure and increasing temperature, minerals recrystallize and align in parallel bands, producing the visible sheets or slaty, phyllitic, or schistose textures. This alignment gives the rock a layered appearance and is the hallmark that distinguishes foliated metamorphic rocks from other rock types.

Rocks formed by rapid cooling of lava on the surface are igneous, not metamorphic, and show textures from cooling rather than mineral alignment. Rocks that lack a preferred orientation are nonfoliated metamorphic rocks, where minerals are more randomly arranged. Cementation of sediments forms sedimentary rocks, created by loose grains held together rather than being reoriented under pressure.