Noun
chalk and cheese (uncountable)
(Britain, New Zealand, idiomatic) Said of things that are very different, though possibly superficially alike.
Girls in scripts are often pretty but brainless, or geeky and no one likes them, so it's great to find richer roles. Chalk and cheese aspects of people are very interesting to play. Jessica Brown Findlay
But I listen to live recordings of things that I did back in the '70s and then how I've done things since. And there's no doubt about it: if I compare the two, it's like chalk and cheese. Rick Wakeman