If all the pearls in the necklace that you choose are perfectly spherical in shape and of the same size, the chances of it being made from cultured pearls are more, as it is very difficult to find natural pearls that are perfect in shape and size. (And if you do happen to come across a necklace made from natural pearls, it is bound to cost you a fortune!)
In what can be best defined as the defense mechanism of this animal, the mollusk starts secreting nacre―a calcium carbonate substance―within its body and covers the intruder. This deposition of nacre on the irritant continues over the period and the resulting build-up of calcium carbonate ends up with formation of a pearl.
The entire process by which oysters make pearls takes place over a period of several years and occurs very rarely, which explains the rare nature of these pearls. At the same time, there is no guarantee that the resulting pearl will be perfectly spherical in shape as we often imagine it to be.
This is the most prominent difference between the two. Owing to their rare nature, natural pearls had become very costly towards the beginning of the 20th century and therefore, people began farming pearls on their own by intentionally stimulating their formation within the body of a mollusk.
As a result of this, the formation of pearls was not restricted to nature anymore, and it became quite easy to produce pearls in pearl farms. Over the period, cultured pearls supplanted natural pearls owing to their easy availability and identical nature.
Cultured Vs. Natural Pearls
The foremost point of distinction between the two pertains to where they come from. While the formation of a natural pearl is traced to wilderness, cultured pearls are formed at pearl farms.
Similarly, the process by which pearls are formed in the wild is devoid of any human interference, but the process by which cultured pearls are formed is triggered intentionally. However, it is difficult to tell whether the pearl was formed in the wild or at the pearl farm just by looking at it.
In such circumstances, your observation skills may come to your rescue. You need to make a note of the fact that cultured pearls tend to be perfectly spherical in shape, while natural pearls may or may not be spherical.
Similarly, you will see a slightly greenish tinge in cultured ones, which won't be seen in their natural counterparts. Yet another method is to rely on the cost of the pearl necklace. If it is inexpensive, it is likely to be a cultured pearls.
If it is costly, on the other hand, it is more likely to be made of wild pearls. You need to be careful though, as there are some fraudsters out there who sell cultured pearl jewelry as natural pearl jewelry for a hefty price.
In laboratory, cultured pearl is distinguished from a natural pearl using x-ray. When subjected to x-ray, you see the inner nucleus of the pearl, and that helps in determining whether it was formed naturally or it was cultured.