The 31.62-carat Azure Blue diamond has an estimate of $6.5 million to $8.5 millionChristie'sA 31.62-carat fancy blue diamond known as the Azure Blue will headline Christie’s Magnificent Jewels auction on June 9 in New York City, where it is expected to draw significant attention from collectors worldwide. Described as the largest fancy blue diamond ever to appear at auction, the stone carries a pre-sale estimate of $6.5 million to $8.5 million.The pear-shaped, modified brilliant-cut diamond boasts VVS1 clarity, with the potential to be reclassified as internally flawless, according to a report from the Gemological Institute of America. It is also classified as a Type IIb diamond—a rare category distinguished by the presence of boron impurities, which not only impart the gem’s vivid blue color but also make it electrically conductive. Such diamonds account for less than 0.1% of all natural diamonds, underscoring their rarity and desirability.The Azure Blue is mounted on a platinum ring and accented by a frame of pink round diamonds. The diamond is being offered by Christie’s in partnership with The Fine Art Group, a London-based independent global advisory firm specializing in art, jewelry, luxury collectibles and other passion assets.The Azure Blue is one of two significant blue diamonds leading the sale at Christie’s Rockefeller Center saleroom. The second is a 5.04-carat fancy vivid blue diamond, also estimated at $6.5 million to $8.5 million. Despite its far smaller size, the stone’s classification as “fancy vivid”—one of the highest intensity grades on the color scale—elevates its value. The marquise modified brilliant-cut diamond has VVS2 clarity and, like the Azure Blue, carries the potential to be internally flawless. It is likewise a Type IIb diamond and is set in a platinum ring with tapered baguette-cut diamonds.5.04-carat fancy vivid blue diamond has an estimate of $6.5 million to $8.5 millionChristie'sMORE FOR YOUClaibourne Poindexter, Christie’s Americas head of jewelry, said the simultaneous offering of two blue diamonds of this caliber reflects both market dynamics and collector demand at the highest levels.“Over the past decade, we’ve seen sustained interest from collectors who understand how rare these stones are, particularly in larger sizes and higher clarities,” he said. “Stones of this caliber, in these sizes and color grades, are extraordinarily scarce. Their appearance together in a single sale underscores both the strength of the category and the continued appetite among collectors for the rarest colored diamonds.”The identical estimates assigned to the two stones—despite their significant size disparity—highlight the importance of color grading in determining value. While the Azure Blue is classified as “fancy,” the 5.04-carat stone’s “fancy vivid” designation indicates a more intense saturation, which commands a premium in the market.According to GIA, the color grading scale for blue diamonds ranges from faint to fancy dark, with intermediate steps including very light, light, fancy light, fancy, fancy intense, fancy vivid and fancy deep. Among these, fancy vivid diamonds are generally the most commercially desirable due to their strong saturation and balanced tone, while fancy deep stones are considered the rarest.Color is the single most important factor in evaluating a blue diamond and is assessed through three primary components: hue, tone and saturation. The most valuable stones display a pure blue hue with strong saturation and minimal secondary colors. The presence of modifying hues—such as gray—can diminish value, while a clean, intense blue is considered the ideal.