A diamond rivière necklace with 51 “Triple X-cut” rated diamonds sold for $1.2 million at Bonham’s New York Fine Jewelry sale Monday. Triple X (also known as “Triple Ex”) is an informal designation that means a diamond that has received excellent polish, symmetry and cut grades. Only round and round brilliant cut diamonds can receive this designation. Each diamond in the necklace is accompanied by a GIA report that states it’s three excellence grades. The graduated line of 51 round brilliant-cut diamonds weighs more than 70 carats.