Diamonds! Museum of Natural History, Washington D.C. Right: The Hazen Diamond Necklace. The 325 diamonds in the platinum necklace weigh a total of 131.4 carats. Designed by the best: Harry Winston! Right: Marquis Diamond Ring. 28.3 carats. Designed by Cartier. This gem is set with 66 diamonds fashioned into a garland ring in a platinum mounting.