Answer:
I plow and plow but never sow.
My first is in riddle but not in little. My second is in think but not in brink. My third is in thyme but not in time. My fourth is in mother but not in brother. My last is in time but no t in climb.
Taken from a mine and then locked up in a wooden case. I am used by students everyday.
I am put on the table, cut, but never eaten. What am I?
I can be repeated but rarely in the same way. I can't be changed but can be rewritten. I can be passed down but should not be forgotten.
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.