Agate is just a chalcedony w/ banding. Most agates form in volcanic rock formations. The cavities which form in molten rock are filled in over time w/ different layers of silica matter. In the case of this birdseye agate that banding activity occurs in concentric rings forming this pattern of circles. I don't know for sure where the particular name "birdseye" came from but it does remind me a lot of the birdseye maple floors in the house I lived in while getting a degree. Thinking back, that was a marvelous old house which needed tender loving care more than a bunch of college students.