A worthy person, as yet lacking polish (5,7)
I believe the answer is:
rough diamond
'a worthy' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rough diamond that I've seen before include "Good guy with uncouth manner" , "Unsophisticated chap - uncut stone" , "Geezer" , "Good but uneducated person" , "a trump, but low" .)