* "Pigeon blood" ruby by Cartier nets record $30.42 million
* Pink diamond belonged to niece of Emperor Napoleon I
* Coloured diamonds and natural pearls fetch strong prices
By Stephanie Nebehay
GENEVA, May 12 (Reuters) - A Burmese ruby weighing 25.59 carats sold for a world record 28.25 million Swiss francs ($30.42 million) at Tuesday's auction that saw strong demand for coloured stones and exceptional natural pearls, Sotheby's said.
"The Sunrise Ruby", the star lot that had the rare grading of 'pigeon's blood' colour, was hotly disputed by two telephone bidders. From a private collection of Cartier jewels, it had been estimated at 11.7 million to 17.5 million Swiss francs.
"A new record price for a ruby," David Bennett, the chairman of Sotheby's international jewellery division who conducted the auction, said as he brought down the hammer to applause.
"In over 40 years, I cannot recall ever having seen another Burmese ruby of this exceptional size possessing such outstanding colour," he said before the Geneva sale.
A historic pink diamond fetched 14.8 million Swiss francs ($15.94 million). Graded fancy vivid pink, it is believed to have been part of the incredible jewellery collection of Princess Mathilde Bonaparte, niece of France's Emperor Napoleon I, according to the auction house.
"The exquisite 8.72 carat stone only recently resurfaced, having been kept in a bank vault since the 1940s," Sotheby's said. Neither the seller nor the buyer were identified.
Including the buyer's premium, the pink diamond sold to a man bidding in the centre of the room, within the range of its pre-sale estimate of 13.6 million to 17.5 million Swiss francs.
"The market for coloured diamonds and precious gemstones has never been stronger, and pink diamonds rank among the rarest of all," Sotheby's said in a statement.
A rare natural pearl necklace, composed of two graduated rows strung with a total of 78 pearls, soared to 6.5 million Swiss francs, setting a world auction record, Sotheby's said.
In all, 453 of 484 lots found new owners, netting a total of 149.85 million Swiss francs at the semi-annual jewellery sales taking place in the Swiss city this week while art auctions are held in New York.
A Picasso oil painting from 1955 smashed the record for the most expensive artwork ever sold at auction when it soared to $179.4 million at Christie's in New York on Monday.
At Christie's in Geneva on Wednesday, a diamond brooch given by Spain's King Alfonso XII to his wife as a wedding gift and ruby ear pendants once owned by Jacqueline Kennedy Onassis are among highlights of a sale that could fetch more than $80 million.
($1 = 0.9287 Swiss francs) (Reporting by Stephanie Nebehay; Editing by Tom Heneghan)