a rough diamond
Someone or something that is unrefined but has many exceptional aspects or underlying potential. Primarily heard in UK, Australia. The young actor was a rough diamond. With some training, she'd become a superstar.
a rough diamondmainly BRITISH or
a diamond in the roughAMERICAN
1. If you call someone, especially a man a rough diamond, you admire their good qualities, even though they are not very polite or well-educated. Note: A rough diamond is a diamond that has not yet been cut and polished. Marden was the rough diamond of the three, feared for his ruthlessness but respected for his First World War Military Cross. I liked Neil Murphy, who is somewhat of a diamond in the rough.
2. If you call someone or something a rough diamond, you mean that they have talent or good qualities which are hidden or not well developed and could be developed more. Note: A rough diamond is a diamond that has not yet been cut and polished. British first novels are more likely to be rough diamonds, with flashes of inspiration in an imperfect whole. When I heard this lady sing, I ran to the theater, and I said, `Chick, I found myself a diamond in the rough.'
a rough diamonda person who has genuinely fine qualities but uncouth manners. informal
Literally, a rough diamond is a diamond before it has been cut and polished. A North American variant of this expression is a diamond in the rough .
a ˌrough ˈdiamond(British English) (American English a ˌdiamond in the ˈrough) a person who has many good qualities even though they do not seem to be very polite, educated, etc: Don’t be put off by your first impressions — he’s something of a rough diamond.
A rough diamond is a diamond that has not yet been cut or polished.