Vintage Opalescent Plate Moonstone
This vintage opalescent plate has a hobnail design on the back, and has been referred to as "moonstone". This description fits, as the coloring is similar to what you see in a moonstone. The plate is around 6.5" and most likely was used as a snack plate of some sort. There is very little wear, with a few scratches but nothing that takes away from this piece.