Answer:
A dragons tooth in a mortals hand I kill I maim I divide the land.
I need to be taken from you before you can have me.
I always have to work with something in my eye.
What is black when you buy it red when you use it and gray when you throw it away?
I have no voice but I can teach you all there is to know. I have spines and hinges but I am not a door. Once I've told you all, I cannot tell you more. What am I?
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.