Answer:
I am pronounced as one letter written with three. I come in blue black brown or grey. Reverse me and I read the same either way.
Taken from a mine and then locked up in a wooden case. I am used by students everyday.
I have cities without people forests without trees and oceans without water. What am I?
Though not a plant I have leaves. though not a beast I have spine. Though many wouldn't need me I am more valuable than wine.
You can see me in water, but I never get wet. What am I?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.