Answer:
What can you throw but not catch?
Not born, but from a Mother's body drawn. I hang until half of me is gone. I sleep in a cave until I grow old. Then valued for my hardened gold.
They belong to me; they belong to you; They can make you feel happy or make you feel blue; They never end until the day you do.
I have an eye but cannot see, You'll head inside when you see me.
It's equally comfortable in an orchestra and a geometry textbook. What is it?
You use it between your head and your toes, the more it works the thinner it grows.