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The pearl is the only gemstone created by a living organism - the oyster. Oyster shells that grow pearls are used for a variety of creations because of the layer of nacre and the edible oyster flesh which is renowned delicacy across the world. The oldest record on pearls dates back to about 2300 BC as the 8,000-year-old pearl was found during excavations at Marawah Island, UAE.
The origin of pearls can be natural or cultured. Natural pearls are very rare, they are formed naturally in mollusks (humans are not involved in the process). The process takes place when parasites such as sand or other foreign bodies enter the mollusk. Over time, the mollusk covers the foreign body with a nacre- and that's how the pearl is born.
Nacre is the inner layer of the mollusk shell formed by thin plates of calcium carbonate and organic materials. However the chemical composition of pearl and nacre remains the same. Notably the cost of a naturally formed pearl is very high because its entirely natural formation excluding the human interruption. Did you know that natural pearls that had been contained in the shell can reach for up to 50 years and longer, however they are a true rarity. One pearl could cost hundreds of thousands of dollars.
Cultured pearls, just like natural pearls, are cultivated in mollusks, but the process itself is different - the main body ( kernel) is planted into a mollusk. It takes from eighteen months to four years for it to grow (depending on the type of pearl). Cultured pearls are grown all over the world, however the main countries of cultivation are Japan, China, Australia, the Philippines, and Vietnam. Cultivated pearls can be divided into seawater or freshwater. There are four main types of cultured pearls: the saltwater Akoya, the Tahiti and the South Seas, and the freshwater.