Box; mineral (4)
I believe the answer is:
spar
I believe this is a double definition.
'box' is the first definition.
(spar can mean to box)
'mineral' is the second definition.
(I know that spar is a type of mineral)
(Other definitions for spar that I've seen before include "A mineral; nautical pole" , "Mineral; strong pole" , "What boxers do" , "Crystal - box" , "possibly rigged" .)