Answer:
Taken from a mine and then locked up in a wooden case. I am used by students everyday.
The person who makes me doesn't need me. The person who buys me doesn't use me. The person who uses me doesn't know it. What am I?
I am put on the table, cut, but never eaten. What am I?
I am all around you, but you cannot see me. I have no throat, but you can hear me. Valued during summer but despised in the winter. What am I?
I am the key that is the hardest to turn
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.