Los Angeles–Bonhams and Butterfields will auction off what is believed to be the world’s second-largest documented pearl, a five-pound gem found off the coast of the Philippines that has been dubbed the "Palawan Princess."

The natural non-nacreous pearl was found in saltwater near the Philippines’ Palawan island and "bears an uncanny resemblance to a human brain," the auction house said. Both rare and immense, the gem is thought to be surpassed in size only by the 14-pound "Pearl of Allah," an approximately 14-pound, 31,893.5-carat pearl that, like the Palawan Princess, was the product of the giant clam shell Tridacna gigas and was also found off the coastal waters of the Philippines.

The approximately 11,339-carat Palawan Princess is a blister pearl measuring six inches in diameter and accompanied by the lower half of its original giant clam shell, which shows the point of attachment where the pearl formed.

The pearl, which will be on the auction block at Bonhams and Butterfields’ Dec. 6 holiday auction of Natural History in Los Angeles, is valued at $300,000 and $400,000.

"This is an once-in-a-lifetime look at one of nature’s most unique treasures," said Mitch Jacubovic, director of EGL USA, one of the labs that was asked to examine the pearl,  in a media release. "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."

In addition to the Palawan Princess, the Natural History will offer a diverse array of objets
d’art, unusual gemstones, and gold, gold nuggets and native metals.

An illuminated music box, "The Winter Palace," crafted under the direction of the German lapidary artist Manfred Wild, is expected to fetch between $250,000 and $300,000. The box was fabricated from rock crystal quartz, diamonds and aquamarines, and designed in the form of a Russian onion-domed palace tower.

The auction will also feature the 47.80-carat "Cat’s Meow" cat’s eye chrysoberyl ring, estimated at $120,000 and $140,000, as well as an orange-pink Padparadscha sapphire weighing in at 18.36 carats. The pear-shaped gem’s estimated value is between $350,000 and $400,000. Another immense stone set to draw attention is the "Holt Kunzite," a 722-carat, emerald-cut Brazilian kunzite with an estimated value of between $35,000 and $45,000.

Among the offerings of gold, gold nuggets and native metals is the "Bonsai Tree," a gold specimen discovered at the Eagle’s Nest Mine in Placer County, Calif., and noted for its appearance of a gnarled bonsai tree as well as for its arborescent crystal habit with branch-like aggregates of flattened gold crystals. Perched on a hillock of white quartz, the specimen is estimated at between $150,000 and $170,000.