Tiffany & Co Platinum Tanzanite and Diamond Ring. 6.51ct TanzaniteTiffany & Co Tanzanite and Diamond ring. This beautiful ring features an Oval Tanzanite stone weighing 6. 51 carats. This stone is surrounded by a single row of Brilliant cut diamonds surrounding the centre stone as well as on the body of the ring and along the shoulder of the shank. Total diamond weight: 1. 22 carat of Internally Flawless to VS 2 range. Current finger size: 6. This ring can be resized. Hallmark: Tiffany & Co. Very Good Condition.