grammaticality - Some kind of + (singular or plural)?

I have a question about using the phrase "some kind of _".

Is it incorrect to say "some kind of + plural noun"?

For example, is it wrong to say "are these rock-like things some kind of chocolates?"

I didn't use "kinds" and that kind of adds to my question. Is "kind" always plural, like "some kinds of chocolates"? Because although I'm using "some", it feels like "kind" shouldn't be a countable noun.

Anyway, I don't think I've heard of "some kind of + plural", but I think it makes more sense then using singular, since I think chocolates are countable. Please help!