Probably dating from the 1940's and measuring 1 & 1/2" x 1 & 5/16" NBS Large. I believe this to be Lucite. It is shaped similar to a Pringle potato chip! It has a red glass jewel set in metal in the center. There is some slight surface scratching to the glass. It has a metal loop shank inserted in the back and connecting to the jewel. $8