Tiffany & Co. 18k White Gold and 14.5mm Black Onyx Bead Necklace Consign Now DeptJewelrySize14.5mm Length 16.5 in. Tiffany & Co. 18k White Gold and 14.5mm Black Onyx Bead Necklace, clasp stamped Tiffany & Co. 18k Length 16.5 in. Please note that this auction has ended. Click here for an overview of this auction.