Pearls are unique gemstones that have been considered symbols of beauty for hundreds of years. Pearls are known as organic gemstones because they are found inside living animals.
They are most commonly used in jewelry, but are also used to make paint, make-up, home decorations, and medicine.
Pearls are natural substances created by shelled mollusks (oysters, clams, and mussels). A pearl is made when a foreign object such as a parasite or a food particle is caught inside a mollusk shell. The mollusk will then produce a fluid composed of conchiolin and aragonite. Aragonite, which is also known as nacre, is the substance that makes up the lining inside of the mollusk's shell.
The mollusk covers the foreign object with layers of this fluid in order to protect itself. The layers build up and harden to form a pearl. Mollusks that live in saltwater oceans produce saltwater pearls. Mollusks that live in the fresh waters of ponds and lakes produce freshwater pearls. Freshwater pearls tend to have a more irregular shape, whereas saltwater pearls are more round. Both saltwater pearls and freshwater pearls can be produced naturally, cultured, or imitated.
Natural pearls are created without any human help, and these are the rarest type of pearls. According to the American Museum of Natural History, only one in 10,000 mollusks will naturally produce a pearl. Natural pearls come in several different shapes, sizes and colors. Perfectly round natural pearls are exceptionally rare making them the most valuable. Since naturally occurring pearls are are so uncommon, most pearls that are sold in stores are cultured pearls.
Cultured pearls are formed with human help. To culture a pearl, a pearl farmer inserts a piece of mantle tissue (thin tissue that connects a mollusk to its shell) from a donor mollusk to the mollusk that will be harvested. A small shell bead is then inserted next to the implanted mantle tissue. The mollusk will secrete layers of nacre on the bead until it becomes a pearl in 2 to 3 years. After the pearl is harvested, it is washed, bleached, and polished.
A bead is not necessary to culture freshwater pearls. Only the mantle tissue will be inserted to make a pearl. Freshwater mollusks are able to form several pearls at the same time; therefore, these pearls are less expensive than saltwater pearls.
Imitation pearls are completely fabricated. Imitations can be made with plastic, glass, ceramic, and mother-of-pearl beads. These beads are covered with paint and other substances to make them look like real pearls. There are several experiments you can do to determine whether a pearl is real or an imitation. Brush the pearl along your front teeth. If the pearl has a rough texture, it is probably a real pearl. If the pearl is smooth, it is likely an imitation. You can also inspect the pearl for imperfections. If a pearl looks polished and completely flawless, it is probably an imitation.