Answer:
I am lighter than the material I am made of. You see parts of me but more of me is hidden underneath.
With three eyes and as black as night I frequently knock down ten men with a single strike!
Who plays when he works and works when he plays?
What's made of water but if you put it into water it will die?
I'm white and used for cutting and grinding. When I'm damaged, humans usually remove or fill me. For most animals I am a useful tool. What am I?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.