It's washed out but it's from one of my large fowl Ameraucanas (blue). Got one like it from a LF Blue Copper Marans the other day. I call them fart eggs.
I get one like that occasionally too. Did it have any yolk in it? We had one that had an itty bitty yolk.
I went to a seminar at A&M for small flock owners. Learned how to grade eggs (got my certificate!) and learned about the anatomy of chickens and eggs. It was very interesting. The way and egg is formed is amazing.