I had a rather experience that taught me just how very sharp a piece of obsidian can be.

I gave a chunk of it to each of two little nieces of mine, because the rocks were beautiful and the little girls wanted them.

A few moments later I asked to see the rocks again and to my chagrin the little girls' tender little palms were crisscrossed with tiny little bloody cuts.

Even then they didn't want to give them up.