Answer:
I am always hungry, I must always be fed. The finger I lick will soon turn red.
It holds most knowledge that has ever been said. But is not the brain, is not the head. To feathers and their masters, it's both bane and boonΒ One empty, and one full.
Talks like this, a green wise man does. Guess my clue, you will.
It can pierce the best armor and make swords crumble with a rub, yet for all its power It can't harm a wooden club.
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.
Long and slinky like a trout, never sings till it's guts come out.