Gems from oysters (6)
I believe the answer is:
pearls
'gems from oysters' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pearls that I've seen before include "Lustrous structures in bivalves" , "Oyster jewels" , "Lustrous structure in an oyster" , "Precious particles in shellfish" , "Beads from 26dn" .)