Answer:
If a man carries my burden they will get crushed to death. Though not rich I leave silver in my track.
I save lives on the ground and in the air. What am I?
What gets sharper the more you use it?
I'm white and I'm used for cutting and grinding. When I'm damaged people usually remove me. What am I?
What can travel all around the world without leaving its corner?
Of these things - I have two. One for me - and one for you. And when you ask about the price, I simply smile and nod twice.