Victorian Gold Filled Banded Agate Center Filigree Brooch with Seed Pearl Detailing has a shiny black base . I am not sure if it is jet or onyx. This absolutely gorgeous piece has a high set piece of banded agate that is the darkest of browns with a cream band. The brooch itself measures approximately 2 by 1 3/4 inches. There is a loop with a jump ring that a chain can be put through on the back. The pin back is more of a silver than a gilt color, and could possibly be a replacement. An absolutely gorgeous piece of jewelry that has been loved, this is one to keep and pass along through the generations.