diamond in the rough
noun/ˌdaɪmənd ɪn ðə ˈrʌf/
/ˌdaɪmənd ɪn ðə ˈrʌf/
(North American English) (British English rough diamond)
- a person who has many good qualities even though they do not seem to be very polite, educated, etc.
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diamond in the rough