A giant pearl, which has tipped the scales at 34kg, could be more than 100 years old
The pearl, which measures 61cm by 30cm and has been valued at about $131 million, was found by a fisherman in the Philippines 10 years ago.
Unaware of the value of his find, he kept the pearl under his bed as a lucky charm, where it remained until a fire burnt down his home in Puerto Princesa, Palawan Island, and he ended up showing it to a tourism official.
The pearl, which has now passed authenticity checks, has just gone on display at the Puerto Princesa City Hall, and Aileen Cynthia Maggay-Amurao posted a photo of it online.
Professor Paul Southgate, an expert in sustainable tropical aquaculture at the University of the Sunshine Coast, says the great size of the pearl indicates it came from a giant clam, the largest bivalve mollusk known to humans.
"Giant clams can live to well over 100 years, and looking at the size of it, it came from a very large giant clam, so a very old clam," Southgate tells SBS.
"It's clearly grown against the inside of the shell valve, so it's basically developed the same pattern as the shell - it's almost like an impression of the inside of the shell."
Pearls form when a foreign object, such as a parasite or an organism that bores through the shell, lodges itself in an oyster’s soft inner body where it cannot be expelled.
The animal tries to minimise the irritation by secreting calcium carbonate, and a pearl forms.
"It's a rare event to find a pearl of any size, but they are reasonably common in giant clams, compared to some other species," says Southgate.
"In the case of giant clams, they are non-nacreous, so they don't have the colour or the lustre of a normal pearl - it's just a white amorphous mass.
"So the value [of this pearl] is in the rarity, particularly something this size. It wouldn't win any points for beauty."
Professor Southgate says giant clams like the one this pearl came from were more common 50 or even 20 years ago, but they are increasingly rare.
"It's very hard these days to find them this size, particularly in the Philippines where this specimen was found. Over-fishing has been a major problem worldwide with giant clams," says Southgate, who took part in an Australian project to breed giant clams and send them to areas including the Philippines to help with re-stocking and conservation programs.
"Giant clams live in [easily accessible] shallow water environments, so they're sitting ducks in terms of local fisheries and local fisherman.
"Really one of the last strongholds for them is the Great Barrier Reef, where you can still find some that are very large, up to 1.5 metres in size."
Professor Southgate says there may well be even larger pearls out there waiting to be found.
And even the fisherman's faith in the pearl's properties as a good luck charm might carry some weight.
"I think once he sells it he'll have a lot of good luck coming his way!" says Southgate.