The Sky Blue Diamond, an 8 carat blue stone mounted on a Cartier ring, is up for auction at Sotheby's.

The Sky Blue Diamond is graded Fancy Vivid Blue

It's expected to make around $15m-25m in the Magnificent and Noble Jewels sale in Geneva on November 16.

The stone is graded Fancy Vivid Blue, placing it in the top 1% of the world's blue diamonds.

David Bennett, worldwide chairman of Sotheby's International Jewellery Division, comments: "The Sky Blue Diamond is of a wonderfully clear celestial blue…

"This important gem will, I am sure, captivate all collectors of exceptional gemstones."

The record for a diamond at auction was set at $58.2m for the 14.6 carat Oppenheimer Blue at Christie's in May this year.