Translucent birthstone (4)
I believe the answer is:
opal
'translucent birthstone' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for opal that I've seen before include "Delicately coloured gem" , "little jewel" , "Gem stone" , "it may be highly valued" , "Milky white gem" .)