I only know chickens, ducks and geese, not guineas. The "waxy" shell makes me think of a duck egg. What breeds of chickens do you have? Any white layers in there? I would not think it is a chicken egg because "waxy" and "sticky whites" do not really fit as a description of chicken eggs. As I said I don't know guineas, but I would guess if you don't haves any ducks then it must be a guinea egg.
Good luck solving the mystery.