Art Deco/Retro Marcasite Silver Pin - GB Monogram

Gorgeous vintage sterling silver marcasite monogram pin, with initials BG. Everything is in great condition, not a single marcasite stone missing. Art deco influence (it's late deco early retro), with Greek key frame and millegrain settings. Really stunning brooch. It measures 1 1/4" square. According to the US patent number on the back, this pin was made in 1940 or 41. Right at the beginning of WWII. It's marked: Pat no. 220590(8? last number is cut in half), and STERLING.