diamond in the rough

noun2

1. •
   An uncut diamond.

   • He wants to go try his luck at that state park in Arkansas where you can look for diamonds in the rough and you can keep what you find.
2. •
   (figurative) A person or thing whose goodness or other positive qualities are hidden by a harsh or unremarkable surface appearance.

   • Her auto mechanic is a diamond in the rough: tough-talking but honest, even generous.