A pearl is an organic object created by a the small mollusk found inside an oyster. They are iridescent, often round or semi-round but can come in different irregular shapes. Round and semi-round pearls can be used to make necklaces and bracelets but this with oblong or irregular shapes can still be used in jewelry for earrings and pendants. In natural conditions only about one oyster out of 10,000 will make a pearl. When a parasite or a large speck of dust enters the mantel of an oyster with the intention of settling there, the small animal inside will cover it with several layers of calcium carbonate. It can take up to two years for a pearl to be made. As this happens quite rarely in nature, the Japanese years ago pioneered a technique meant to encourage the mollusk to produce one. This entails grafting a fake intruder inside the oyster and let the mollusk do the rest.
These are called cultured pearls and there are several varieties of them. Akoya pearls are rather small and light in color, they were the first cultured pearls and traditionally have been made by the Japanese, although in recent years the Chinese and Vietnamese have also started producing them. When you see Akoya pearls that are dark it means they have been dyed. The Japanese Akoya industry is quite stringent and if you are looking for good quality only buy Akoya branded from Japan. If you like very large one you should look at Tahitian black pearls instead. Although it is called black this is very rarely black but tend to be dark blue or dark green. South Sea pearls are even larger and grow in a very limited sea area between Australia and South China. As they are natural gemstones are not as strong as mineral gemstones and also will require a lot of care to ensure they do not lose their sheen and luster which is what makes them so beautiful.