Its 5/8" tall and 7/16" diameter. The top is some type of plastic or resin "bubble" with silver images under it. The bottom is flat and magnetic. About 7/16" up from the bottom there is a groove approx 1/16" wide and 1/16" deep that circles the item. I don't see any other markings except the images on the top. Doesn't seem to come apart anywhere.
Found at a baseball field behind home plate on a grassy bank.
that it was an earring. Found them w/ Google after you said that. Now I'm curious if there is a way to turn them on/off or if they just stayed on until the battery died.