flake
A slab of rock partially detached from the main face, sometimes paper-thin and resonant when tapped, sometimes thick enough to stand on. In climbing, a flake can be a gift or a hazard depending on how committed it is to staying attached.
Etymology
Likely from Old Norse flakna, to flake off, or flak, a flat piece. The word carries the sense of something in the process of separating.
*
Surprise Me With a Word