Vintage Mexican Mayan Aztec Face Mask Sterling Silver Jade? Onyx? Pendant Brooch

This is a vintage sterling silver round brooch and pendant. It features a green stone (maybe jade or onyx), a silver round medallion with a face mounted on the stone and a filigree border. It is signed on the back, "Sterling 925 Mexico EME". Acid tested for sterling silver. 1.625" x 1.625" In good preowned condition. Some tarnish throughout. A few fleabites on the edge of the green stone as noted in the photos.