Pearls are a mixture of mineral and organic materials formed in the soft living tissue of a shelled mollusk. There are also chemically made pearls that are designed from calcium carbonate (aragonite or a mix of aragonite and calcite).
In their organic form, pearls are formed by shelled molluscs as well as bivalved oysters and mussels. They are made up of nacre which is mostly aragonite (calcium carbonate) and conchiolin (complex proteins forming mollusc shells).
Used as adornments for more than 6,000 years, pearls do not require any processing and yet they show perfect gloss which makes them attractive in their natural state. They are used as gemstones but are not regarded as true minerals due to their organic origin.
White pearls are the most popular variety and they are bleached to lighten the dark spots of conchiolin. However, pearls are also dyed to shades of yellow, pink, gray, silvery-black and chocolate. There are imitations including fish-scale pearl or enamel coated that are produced from the scales of certain fish. There are also pearls made of sea snails, mussels, teeth and mabe pearl as well as some plastic products that are known as faux pearl.
Natural pearls are extremely rare, quite expensive and are typically small. A cultured pearl induces the animal to form a “pearl sac" whose cells secrete a layer of brownish protein known as conchiolin layered over the irritant which can then be harvested.
Natural pearls are found and cultured in waters all over the world. From seas to oceans, they are present in Australia, Japan, Central America, the Persian Gulf, the Gulf of Manaar, the coast of Madagascar, Burma, the Philippines, the South Pacific Islands and South America. Natural river pearls are found in Asia, Europe and North America.
Some of the cultured seawater pearl sources include Southeast Asia, Australia, China, French Polynesia, Japan, Philippines and the South Pacific Islands. The cultured freshwater pearl sources are China and Japan.