Which statement about slate is true?

• A. Slate has no cleavage.
• B. Slate forms from granite.
• C. Slate shows slaty cleavage.
• D. Slate is the highest-grade metamorphic rock.

Answer: (C)

In metamorphic rocks, mineral grains reorient under pressure to form planar features that make the rock split along flat surfaces. Slate forms from shale or mudstone under low-grade metamorphism, and the clay minerals and fine grains align parallel to each other, creating slaty cleavage. This cleavage is what allows slate to be split into thin, flat sheets, a hallmark of slate.

That’s why this statement is true. Slate does not lack cleavage, it does not form from granite (granite is an igneous rock and slate forms from sedimentary rock), and slate is not the highest-grade metamorphic rock (higher-grade rocks include phyllite, schist, and gneiss).