Stone work the French put up (4)
I believe the answer is:
opal
'stone' is the definition.
(gemstone)
'work the french put up' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'the french' becomes 'la' ('the' in French).
'put up' says the letters should be written in reverse.
'la' in reverse letter order is 'al'.
'op'+'al'='OPAL'
(Other definitions for opal that I've seen before include "Lustrous stone" , "Milky stuff that's hard" , "Translucent gemstone" , "Delicately-coloured gem" , "Milky iridescent stone" .)