Chicken or duck egg?

[EmmaKnight]

I received 12 eggs yesterday and I realized one of them was massive. I think it might be a duck egg but I do not know. Here are pictures of the egg (circled in red):

 

[CascadiaRiver]

It could very well just be a large chicken egg, or maybe a double yolker, maybe.

 

[Louise Waffles]

Duck eggs feel different than chicken eggs. Kind of waxy. You can scratch the surface with your fingernail, and some will come off. The shell is much, much thicker, and I think they are heavier than a chicken egg of the same size would be.