Answer:
Taken from a mine and then locked up in a wooden case. I am used by students everyday.
I go through a door but never go in and never come out.
I cannot be burned in fire or drowned in water
First you see me in the grass dressed in yellow gay; next I am in dainty white, then I fly away. What am I?
Man walks over, man walks under, in times of war he burns asunder. What is it?
I am a food with 5 letters. If you remove the first letter I am a form of energy. Remove two and I'm needed to live. Scramble the last 3 and you can drink me down.