We've had plenty of small eggs from the ladies when they first started laying, but this mini egg we got yesterday takes the cake for smallness. Its about half the size of the medium blue egg and almost completely round.
I think it’s called a wind egg. I’ve got a turken hen, maybe 8 years old or so, that ONLY lays wind eggs for the past year. They range in size between a dime and a nickel. It so funny, she’ll make a huge production out of laying an egg and then when I walk over to the nest to find what looks like a small grape.
Fairy, fart, wind, rooster eggs are usually from a tiny piece of tissue breaking loose from the reproductive tract, or an immature ova(yolk) and the body forms an egg around it. Color can be darker than 'normal' as the pigment coating released has to cover a much smaller area so is thicker. Can happen with any age layer, but more common with older layers.
I think it's explained in this excellent video, which is worth watching regardless: