Sapphire or ruby (3)
I believe the answer is:
gem
'sapphire or ruby' is the definition.
(I know that sapphire is a type of transparent gem)
This is the entire clue.
(Other definitions for gem that I've seen before include "one of the Cairngorms?" , "Emerald or sapphire, say" , "perfect specimen" , "Precious or semi-precious stone" , "Pleasant and cheerful (from German)" .)