are an organic gem, so named because they are created by living creatures. Each pearl begins its existence as a piece of grit or other particle that makes its way into the shell of a marine or freshwater oyster. To protect itself from the invasive substance, the oyster coats the particle with layer upon layer of a substance called nacre, or mother-of-pearl, which eventually becomes thick enough to form a pearl.
Pearls are classified by their origins and their shapes.
Natural pearls are formed when an accidental intruder enters a mollusk's shell and continuous layers of nacre grow like onion skins around the particle. Natural pearls vary in shape depending on the shape of the piece being coated.
Natural pearls have always been considered rare and are quite expensive. They are usually sold by carat weight. Most natural pearls on today's market are vintage pearls.
Like natural pearls, cultured pearls grow inside of a mollusk, but with human intervention. A shell is carefully opened and an object is inserted. Shapes of objects vary, depending on the final shape of pearl that's desired.
Over time the object becomes coated with layers of nacre. The depth of the nacre coating depends on the type of mollusk involved, the water it lives in, and how long the intruder is left in place before being harvested. As nacre thickness increases, so does the quality and durability of the cultured pearl.