After Sotheby's sold a 24.78-carat fancy intense pink diamond for a record-breaking $46 million last year, some had expected the auction's headline piece to finish higher.

"When it gets to this price there are only half a dozen people who can actually participate," said Mourad Hatik, a Geneva jewel trader. "If they decide they already have a similar stone, then the price doesn't go up."

Still, exceptional gems such as the Sun-Drop will always attract bidders, he said. "There is very little quality to buy."

The Sun-Drop, which was found in South Africa last year, was put up for sale by New York-based company Cora International.

Gemologists had rated it as fancy, vivid yellow — the highest possible color grading. Yellow diamonds are created by nitrogen impurities being trapped within carbon molecules and hardening over the course of millions of years.

Other lots at the $70 million sale in Geneva's Beau-Rivage hotel included a white cushion-shaped diamond weighing 38.88 carats that sold for almost $7 million, including commission.

A 12.01-carat emerald from Colombia's Muzo mine sold for $1.4 million, while a blue diamond ring was snapped up for $4.3 million.

However, several precious jewels — including an elaborate gold and diamond 'peace dove' brooch, a blue diamond ring estimated at over $7.5 million, and a suite of imperial jewels — failed to find a buyer.

The set comprising a necklace, brooch and pair of earrings was given by the Ottoman Empire's Sultan Abdul Hamid II to the wife of the Khedive of Egypt in the late 19th century.

Sotheby's said some of the gems may have been part of a peace offering given by Russian Czar Peter the Great's wife Catherine to Ottoman Sultan Ahmed II in 1711. A bid of $9.3 million wasn't