Answer:
A precious stone, as clear as diamond. Seek it out whilst the sun's near the horizon. Though you can walk on water with its power, Try to keep it, and it'll vanish within an hour.
No matter how little or how much you use me, you change me every month.
They're up near the sky, on something very tall. Sometimes they die, only then do they fall.
What always runs but never walks, often murmurs, never talks, has a bed but never sleeps, has a mouth but never eats?
A hill full, a hole full; yet you cannot catch a bowl full. What is it?
I’m grown from darkness but shine with a pale light. Very round I am and always a lady's delight.