Sailor going round China for precious stones (5)
I believe the answer is:
opals
'precious stones' is the definition.
(I've seen this before)
'sailor going round china' is the wordplay.
'sailor' becomes 'os' (ordinary seaman).
'going round' is an insertion indicator.
'china' becomes 'pal' (I've seen this before).
'os' going around 'pal' is 'OPALS'.
'for' acts as a link.
(Other definitions for opals that I've seen before include "Milky white and coloured gems" , "Milky sparkling gemstones" , "Iridescent gems" , "Milky-white stones" , "Translucent gemstones" .)