The largest know pearl weights 6.4kg

The largest pearl known, was found in the Philippines in 1934. It is a naturally-occurring, non-nacreous, calcareous concretion from a giant clam. Because it did not grow in a pearl oyster it is not pearly, instead it has a porcellaneous surface. In other words, it is glossy like a china plate. Other pearls from giant clams are known to exist, but this is a particularly large one. The pearl weighs 14 lb (6.4 kg) and was supposedly first discovered by an anonymous Filipino Muslim diver off the island of Palawan in 1934. According to the legend as it is currently told, a Palawan chieftain gave the pearl to Wilbur Dowell Cobb in 1936 as a gift for having saved the life of his son. The pearl had been named the "Pearl of Allah" by the Muslim tribal chief, because it resembled a turbaned head. Another even more elaborate legend says that this object is actually the Pearl of Lao-Tzu, a cultured pearl created with a carved amulet and then supposedly progressively grafted into several giant clams, before supposedly being lost due to a shipwreck in 1745. ^[6] This legend has been discredited, however because this pearl is indeed the product of a giant clam, Tridacna gigas, which cannot be grafted. The pearl is also a whole pearl, not a mabe pearl, and whole pearl culturing technology is only 100 years old. ^[7]

^{http://en.wikipedia.org/wiki/Pearls#Creation_of_a_pearl}