Answer:
Taken from a mine and then locked up in a wooden case. I am used by students everyday.
With three eyes and as black as night I frequently knock down ten men with a single strike!
I stand in one place yet I fill a whole room. I can be filled with molten rock and come in every hue.
What goes through a door but never goes in and never comes out?
Sing me to a baby about to go to sleep.
If itβs information you seek, come and see me. If itβs pairs of letters you need, I have consecutively three. What am I?