Answer:
A precious stone, as clear as diamond. Seek it out while the sun's near the horizon. Though you can walk on water with its power, try to keep it, and it'll vanish in an hour.
What flies without wings? What passes all things? What mends all sorrow? What brings the morrow?
What lies in a tunnel of darkness. That can only attack when pulled back?
What is pronounced like one letter, written with three letters. And belongs to all animals?
I can be quick and then I'm deadly, I am a rock, shell and bone medley. If I was made into a man, I'd make people dream, I gather in my millions By ocean, sea and stream.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.