Answer:
Slayer of regrets, old and new, sought by many, found by few.
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.
Different lights do make me strange, thus into different sizes I will change
You can always see it, but it's too far away to touch. Mountains rest on it, and at sea it surrounds you. What is it?
The person who makes it has no need for it. The person who purchases it does not use it. The person who does use it does not know he or she is. What is it?
What never gets any wetter no matter how hard it rains?