Auctioneers are shining the spotlight on premium diamonds and gemstones at upcoming auctions, led by the 9.51-carat Mellon Blue diamond, which could fetch US$30 million.

Scheduled for November 11, 2025 in Geneva, Christie’s Magnificent Jewels auction will feature a curated selection of historic and modern jewellery from all periods as well as renowned jewellery houses such as Harry Winston, Cartier, JAR and Van Cleef & Arpels, to name a few.

The star of the auction, however, is The Mellon Blue – an exceptional fancy vivid IF blue diamond weighing 9.51 carats. Standing out as one of the finest fancy colour diamonds ever to appear on the market, Mellon Blue is expected to fetch US$20 million to US$30 million. 

The stone belonged to Rachel Lambert Mellon, better known as American horticulturalist, philanthropist and art collector Bunny Mellon (1910-2014). She owned the blue diamond, then set as a pendant, for decades, according to Christie's.

A 12.56-carat Kashmir sapphire and diamond ring, meanwhile, gets top billing at Sotheby's High Jewelry sale in Hong Kong on September 19, 2025. With a pre-sale estimate of HK$20 million (approximately US$2.6 million), the cushion-shaped Kashmir sapphire is set between two trapeze-shaped diamonds.

It comes with an SSEF report, stating that the sapphire is of Kashmir origin, with no indications of heating and that the colour may also be called “royal blue.”

Other notable pieces expected to turn heads at the Hong Kong auction are a necklace with 21 Burmese rubies weighing 61.91 carats in total and diamond accents, valued at HK$5.5 million to HK$8 million (around US$706,000 to US$1.02 million); a 5.07-carat VS1 cut-cornered mixed-cut fancy pink diamond ring, which could fetch HK$8 million to HK$11.8 million (approximately US$1.02 million to US$1.51 million); and a jadeite and diamond ring, which could sell for HK$8 million to HK$12 million (about US$1.02 million to US$1.54 million).