The second largest pearl ever found is set to go under the auctioneer's hammer next week, and may fetch as much as US$400,000. Weighing 2.25 kg (5 lb), the pearl measures six inches in diameter and bears an uncanny resemblance to a human brain. The auction lot of the massive pearl will include the lower half of the giant clam (Tridacna Gigas) in which it formed in the coastal waters of the Philippines.
Dubbed the “Palawan Princess”, the gargantuan non-nacreous pearl has been valued at as much as GBP250,000 (USD400,000). It will go under the hammer in Los Angeles at Bonhams auction of Natural History on December 6, 2009.
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The Tridacna Gigas was first described by Lamarck in 1758, and is known as the true "Giant Clam". Reaching lengths of greater than 4 ½ feet (1.4 meters) and weighing hundreds of pounds, the Giant Clam can live well past 50 years of age. This is the largest species of bivalve mollusk to have ever lived in the fossil record of our planet. The Tridacna Gigas can still be found in the waters of the Pacific stretching from the Philippines to Micronesia.
According to Mitch Jacubovic, the director of gemologists at the European Gem Laboratories USA in New York: "This is an once-in-a-lifetime look at one of nature's most unique treasures. 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."
David Bidwell, a senior appraiser with Universal Gemological Services, called it "clearly one of the most valuable pearls of its kind in the world today."
Almost any shelled mollusk can, by natural processes, produce some kind of "pearl" when an irritating microscopic object becomes trapped within the mollusk's mantle folds and the conditions are correct. Interestingly, not all "pearls" are made of nacre, that combination of aragonite (calcium carbonate and conchiolin that is secreted from a mollusk and layered together to form what gemologists call a "nacreous" pearl.
Some marine animals—namely snails and clams—produce gorgeous gems made up of non-nacreous calcium carbonate. Calcite, rather than aragonite is the primary material here and they are, thus, technically classified as calcareous concretions. A pearl that is not "mother-of-pearl", might best be qualified "porcelaneous." It indeed possesses a brilliant luster like porcelain, a hard resistant appearance, and occurs in a variety of colors according to the species producing it.