I had a light brahma bantam lay one the size of a marble if not smaller. I cracked it open and there was no yolk of course. I thought for a second a wild bird had gone in there and layed an egg.
one of my mutt breeds first eggs was as small as a marble, i know, it sounds crazy but its true and I had to see the inside and low and behold it was perfect only tiny, yolk sac and all. i did'nt think about taking a pic and am kicking my own rear now.