Sotheby's said Monday it would auction a pair of "phenomenally rare" blue and pink diamond earrings next month that together may fetch up to $68 million.

"The 'Apollo and Artemis Diamonds' will be the stars of our May sale in Geneva -- by far the most important pair of earrings ever offered at auction," David Bennett, worldwide chairman of Sotheby's international jewellery division, said in a statement.

The earrings comprise two large pear-shaped gems of different hues.

They will go on the block separately on May 16, the auction house said, adding that the seller wished to remain anonymous.

The 14.54-carat Apollo Blue, which is described by Sotheby's as "the largest Internally Flawless Fancy Vivid Blue diamond ever to be offered at auction", is estimated to fetch between $38 million and $50 million.

The 16-carat Artemis Pink, with its "Fancy Intense Pink" hue, meanwhile, is expected to rake in $12.5-18 million.

The diamonds were named after Apollo, the Greek god of music and of the Sun, and Artemis, his twin sister, who was goddess of the hunt and of the Moon.

In Greek and Roman mythology, diamonds were believed to be the tears of the gods.