Antique mother of pearl brooch.

This was given to me in the 70’s by an aged aunt. She said it was very old. I’m guessing maybe 30’s, but I honestly have no clue. It measures 2” by 1 1/4.” The little hook to the bar is gone, but an adhesive pin back could be used. Light as a feather and some kind of antique plastic possibly. She is a tad worn, predictably from her age.