Work on a figure in stone (4)
I believe the answer is:
opal
'stone' is the definition.
(I've seen this before)
'work on a figure' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'on' is a charade indicator (letters next to each other).
'figure' becomes 'l' (I've seen this in other clues).
'op'+'a'+'l'='OPAL'
'in' is the link.
(Other definitions for opal that I've seen before include "raw material" , "Delicately-coloured gem" , "Milky stuff that's hard" , "Milky iridescent stone" , "Birthstone for October" .)