18k Yellow Gold Plated Sterling Silver Blue Topaz and Diamond Pendant Necklace , 18" Gemstones may have been treated to improve their appearance or durability and may require special care. The natural properties and composition of mined gemstones define the unique beauty of each piece. The image may show slight differences to the actual stone in color and texture. Blue Topaz is December's birthstone. All our diamond suppliers confirm that they comply with the Kimberley Process to ensure that their diamonds are conflict free.