Photos: Rare Kashmir sapphire glitters in Geneva auction

Geneva: The largest Kashmir sapphire ever auctioned and a royal tiara which everyone can try on via Instagram are the stars of this year's May magnificent jewels sales in Geneva. Gems worn by French emperor Napoleon Bonaparte's adopted daughter also dazzle among the historic treasures being sold by Sotheby's and Christie's auction houses on May 11 and 12.

The Kashmir sapphire, a 55.19 carat gem, was formerly in the collection of Maureen Constance Guinness, a marchioness of the aristocratic Anglo-Irish brewing family, who died in 1998. Kashmir sapphires of over 30 carats are very rare.

It is being sold alongside a cushion-shaped Kashmir sapphire weighing 25.97 carats and the pair are estimated to fetch $2-3 million.

Following their discovery in the early 1880s, the mining of Kashmir sapphires only lasted from 1882 and 1887, making such gems some of the most coveted on the market, according to Sotheby's.

They have a rich cornflower blue hue with a soft, velvety texture, and retain their lustre in any light. "Kashmir sapphires are among the rarest coloured gemstones known to man," said Benoit Repellin, head of magnificent jewels sales at Sotheby's in Geneva. "These gems have over the years acquired an almost legendary status."

Among the other historical pieces on sale is a tiara kept for more than 150 years in the Italian House of Savoy royal dynasty. The diadem, containing 11 natural pearls and diamonds, dates from the second half of the 19th century and is estimated at $1-1.5 million. Sotheby's said it was witnessing unprecedented global demand for royal jewellery, particularly from younger clients in Asia.

Collectors from that continent have bought a third of the tiaras sold by the auction house in the past five years. Keen to attract the interest of a new generation, Sotheby's created an Instagram filter that allows people to create a picture of themselves wearing the Savoy tiara in a sumptuous Italian palace.

In the big gems category, Christie's is offering a rectangular white 100.94-carat diamond called the Alrosa Spectacle, valued at $12-18 million. The internally flawless diamond is the largest stone ever to have been cut in Russia and was cut from a rough stone unearthed in the remote northeastern Yakutia region in 2016.

Other standout items include a pendant set with a 104.40 carat pear emerald, mounted by US jeweller Harry Winston, offered by Sotheby's for $1-1.5 million. It is a "really exceptional weight for emeralds, which are more fragile stone", said Repellin.