I live on the coast & you are correct, it takes little time to smooth off hard pieces of material. Beach glass comes to mind. I've collected volcanic rock from Oregon beaches that is smooth as a cue ball, the same stuff in the mountains is rough with sharp edges. Extremely hard material.I’m far from any costal action but I’ve seen other posts showing how the ocean can erase flake scars, just a hunch from an ignorant Kansan but I think it could at least be a large flake.
Edit: I’ll leave my previous thought up but I was thinking I doubt it would be sharp if there was enough wave action to erase the scars so maybe the others are right