925 sterling silver diamond cut ring with a gorgeous faceted marquise solitaire black onyx stone. The stone set in the middle measures 3/16 inch wide. It is available in sizes 5, 6, 7, 8, and 9. Onyx is a variety of chalcedony. For millennia, artisans have carved intricate cameos from black-and-white onyx. Solid black onyxes, faceted or cabbed, are also popular jewelry stones. It is the birthstone for December.