At the mountains we used to have black snakes regularly hanging around the basement rafters, because they were attracted to the steady diet of stubborn mice who used to live there.
One day I was weeding near the house and found four of their eggs slightly underground. They were 1 1/2 inch off-white ovals, and the texture of their shells was leathery.
I did have to break them all, because we had remodeled and wanted to be rid of both mice and snakes.
I don’t know why—what else would I expect?—but I was surprised that they had albumen and a yellow yolk just like a bird egg!