The Bulgari Laguna Blu is an 11.16-carat Fancy Vivid Blue diamond, a color so rare it occurs in less than 0.02% of all diamonds. Natural blue diamonds form when boron atoms enter the crystal structure deep within the earth — a condition so specific that most mines will never produce one. Stones above 10 carats with this level of saturation are almost unheard of. That rarity is why the Laguna Blu achieved nearly $25 million at auction, becoming one of the most valuable blue diamonds ever sold. Th