Free cameo -- finally in favourite stone (7)
I believe the answer is:
peridot
'stone' is the definition.
(type of precious stone)
'free cameo finally in favourite' is the wordplay.
'free' becomes 'rid' (to be free of something is to be rid of it).
'finally' says to take the final letters.
'in' is an insertion indicator.
'favourite' becomes 'pet' (synonyms).
The final letter of 'cameo' is 'o'.
'rid'+'o'='rido'
'rido' going into 'pet' is 'PERIDOT'.
(Other definitions for peridot that I've seen before include "Pale green gemstone" , "I deport (anag) - gemstone" , "olivine" , "mineral" , "Gemstone -- pre-do it (anag)" .)