Approximately 4.1cm x approximately 3.6cm. Please forgive any errors as this was measured by an amateur. Purchased in the United States over 30 years ago. I purchased marcasite accessories at the same store at the same time. Most of them have a 925 stamp on the back, but this one doesn't have one. There is no stamp, but I believe it is sterling silver, although I have no certainty. I have never used it after purchase, but I have selected "Like New" because it has been stored for a long time. I hope you understand that it has been stored at home for a long time. #Vintage #Brooch #Marcasite #Accessories #Onyx #Earrings #Clip