This is a sterling silver (with rhodium plate) and enamel BPOE Elks pin which also has a faceted clear glass piece made to mimic a diamond. Probably a lapel pin given the screw back closure. Made by Uncas, nice!
Hallmark: Sterling U (with arrow)
Size: 1/2" x 1/2"; Grams: 1
Condition: Excellent vintage - minor wear to the rhodium plate