What am I?

Taken from a mine and then locked up in a wooden case. Never released but used by students everyday. What am I?

With the rich I am blue, with the poor I am red, with the amphibian I am cold but with the dog I am hot instead, What am I?

Take away my first letter, take away my second letter, take away all my letters and I would remain the same. What am I?

I have wheels and flies, yet I am not an aircraft. What am I?

Riddles and Answers