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.
Two bodies have I, though both joined in one. The more still I stand, the quicker I run.
What goes in the water red, and comes out black?
Weight in my belly, Trees on my back, I travel fast in my place, but feet is a feature I lack
In your fire you hear me scream, creaking and whining, yet I am dead before you lay me in your hearth.
Iām grown from darkness but shine with a pale light. Very round I am and always a lady's delight.