Hidden gems is an idiom which means something which is extremely outstanding and not many people may know about; for example, Blame It on Rio by Stanley Donen is a good movie, but relatively unknown by the mainstream world, hence a hidden gem.
Hidden gem however does seem to be informal, is there an alternative phrase for this which I can use in a formal context?
It is also known as a diamond in the rough, which is defined as;
someone or something whose good qualities are hidden
Best Answer
I don't know if there is an idiom that covers everything, but you may find use in these:
few and far between (rare and difficult to find)
scarce
once in a blue moon (rare event)
hole in one (rare achievement)