Natural pearls, on the other hand, are formed naturally by free-range "wild" oysters living at sea without any encouragement from humans. When a natural irritant such as a fragment of shell, a scale or a parasite becomes lodged inside an oyster or mollusk, it gets coated with layer upon layer of nacre. Contrary to popular belief, grains of sand do not form pearls. If sand were enough of an irritant, our ocean floors would be littered with millions of natural pearls! Natural pearls are actually very rare, mostly because pearl-producing species of mollusks were nearly hunted to extinction with most natural beds of pearl-bearing oysters depleted by over-harvesting in the 18th and 19th centuries. Today, natural pearls are extremely rare. Only 1 in about 10,000 wild oysters will yield a pearl and of those, only a small percentage achieve the size, shape and colour desirable to the jewellery industry.
South Sea pearls are cultivated in Pacific countries. The most beautiful of them are from Australia. The larger size, limited cultivation area and longer growing period of South Sea pearls make them the rarest of all pearl types. The luster of South Sea pearls is unique and velvety compared to other varieties of pearls. Only a small number of South Sea pearls are round, so finding matching pearls can be challenging. Many consider Golden South Sea cultured pearls to be the rarest and most valuable in the world.
Tahitian pearls are produced only by black-lipped oysters in the French Polynesia. They became popular in the mid-1970s and are now the second most valuable type of pearl in the world. Colors of Tahitian pearls range from light silver through greens to aubergine or purple, and to quite a dark black. Generally, the darker the pearl, the more valuable it is. True peacock green pearls are typically expensive.
Akoya pearls are cultured seawater pearls that are cultivated mainly in Japan. They were made famous by Kokichi Mikimoto. Akoya pearls are the third most valuable pearls in the world. The average Akoya pearl is only 7 mm. Akoya pearls are naturally round, although each harvest produces some baroque and keshi pearls. These pearls usually have a beautiful and bright luster. The color of Akoya pearls varies widely between natural shades such as white, pink and cream.
Most freshwater pearls are cultivated in China. Their unique shapes range from baroque pearls to round and are almost indistinguishable in shape from Akoya pearls. Freshwater pearls come in many colors, for example lavender, tangerine, mauve, silver, peach and all shades in between. They are cheaper than seawater pearls, but just as durable and shiny. The size of freshwater pearls varies from 5 mm to even 13 mm.
A pearl begins to form when a foreign substance or irritant enters the shell. This irritant acts as the core of the pearl. The different shapes are based on what shape of core is implanted in the shell.
Round pearls are usually the most desirable of all pearl shapes and also the most valuable. These pearls are perfectly round.
The drop-shaped pearls are named after teardrops. These pearls can be very valuable if they have a flawless and symmetrical shape.
Baroque pearls are completely asymmetrical in shape, and no two are alike. Baroque pearls are valued for their uniqueness and price. The term "baroque" comes from the Portuguese word barocco, which means an imperfect, rough or uneven pearl. A French dictionary from 1694 defines "baroque" to describe a pearl that is imperfectly round.
Round baroque pearls are a subgroup of baroque pearls. There are rings around the pearl, which make these pearls very unique.
The word ‘Keshi’ means ‘poppy seed’ in Japanese and these pearls are also sometimes referred to as seed pearls.
Keshi pearls are irregularly shaped and often flat. They are formed when the oyster rejects and spits out the implanted nucleus before the cultivation process is complete, or the implanted shell tissue breaks and forms separate pearl sacs without cores. These pearl bags eventually produce pearls without a nucleus. Keshi pearls can form in either saltwater or freshwater molluscs.
To the untrained eye, semi-round/oval beads can look perfectly round. However, they have microscopic irregularities compared to perfectly round pearls, making them slightly less valuable.