Striped gem (5)
I believe the answer is:
agate
'striped gem' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for agate that I've seen before include "Banded ornamental stone" , "Striped stone" , "Variety of chalcedony" , "Hard stone with concentric bands of colour" , "Semi-transparent stone" .)