a rough diamond

a rough diamond

  (British & Australian) also a diamond in the rough (American & Australian)
a person who does not seem very polite or well educated at first, although they have a good character Mitchell may have been a rough diamond, but he was absolutely loyal to his employer.
See also: diamond, rough
References in classic literature ?
He's not a rough diamond - a pearl-containing oyster of a rustic: he's a fierce, pitiless, wolfish man.
His awe for the mysteries of nature prompted him to get the attention of consumers this holiday season by giving a rough diamond to each client with their purchase of a finished "rock.
There are about five experts in the world that could look at a rough diamond and tell you where it came from.
IDH Diamonds NV, which has extensive experience as a rough diamond dealer and has demonstrated the skills to bring new production to market, will continue to provide consulting services to the sales office.