The second-largest pearl ever found is up for auction next month where it is expected to fetch up to 250,000 pounds, auctioneers Bonhams said in London last Friday.

The 2.25-kilogramme pearl, which measures 15 centimetres across and looks like a human brain, will go on sale in Los Angeles on December 6.

"This is an once in a lifetime look at one of nature's most unique treasures," said Mitch Jacubovic, the director of gemologists at the European Gem Laboratories USA in New York.

"A pearl this size is not only one of the largest ones we've ever seen, it is among the largest pearls ever seen anywhere."

The pearl, which was found in waters off the Philippines, will be sold at auction at the Natural History Museum in Los Angeles alongside the lower half of the giant clam shell where it formed.