Answer:
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?
If you've got me I'm everywhere. If you share me I'm nowhere. What am I?
What has to be broken before you can use it?
You use a knife to slice my head but you weep beside me when I am dead
With three eyes and as black as night I frequently knock down ten men with a single strike!
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.