rough diamond
diamond in the rough AmE

He appears as something of a rough diamond throughout the books.

Far too much the rough diamond for you, I suppose.

I've seen rough diamonds too often to have any doubts.

Being a rough diamond, he has rather been put down by people right from the beginning, and it's sort of eaten into him, you see.

Her second husband is a rough diamond with a shady past.

Many "rough diamonds" have parents who are not high school graduates.

He was a rough diamond and never attempted to polish it.

The discovery of two large rough white diamonds was announced in November 2010.

De Beers controls 60 percent of the world's $8.3 billion market in rough diamonds, but that is down from the 1980's.

Eventually the rough diamond got smooth, and we became friends.