Black Glass Marcasite Button

This is a beautiful black glass button featuring sparkling silver luster/marcasite top. I believe these are genuine marcasites set into a silver luster top on the button. Lots of sparkle. The shank is embedded heavy brass. There is a small mar or imperfection on the back. Can't tell whether it is factory or man made, but it doesn't affect the top of the button. Otherwise in very good condition.