Facts for Kids

Pearls are shiny, hard little gems that grow inside certain shelled animals called mollusks. They look smooth and bright because the animal coats something inside its shell with many thin layers. People have prized pearls for thousands of years and used them in jewelry, clothing, and decorations because they are beautiful and rare.

Some pearls happen by chance in wild animals and are called natural pearls. Other pearls are created on purpose by people who farm oysters or mussels. There are also imitation pearls, which are made from glass or plastic to look like the real thing.

Pearls are mostly made of calcium carbonate, a mineral like the stuff in seashells. The mollusk lays down this mineral in very thin, overlapping sheets. Light hits these sheets and is reflected, bent, and split into colors, which gives pearls their soft glow and sometimes a rainbow-like shine called iridescence.

The more even and thin the layers, the stronger the shine, which people call luster. Pearls that have many thin layers look brighter and smoother than those with fewer, thicker layers.

A pearl is a small, rounded object formed inside the soft part of a mollusk, usually in a fold of tissue called the mantle. When the animal gets something it does not like—such as a tiny grain of sand or a plant bit—it can coat that visitor with smooth layers to keep itself comfortable. Over time those layers build up and form a pearl.

Good pearls are called gemstone-quality because they have a bright shine and even shape. But many pearls are irregular, dull, or shaped oddly, and those are less valuable or kept as curiosities.

A natural pearl begins when a tiny intruder — like a small grain or a tiny animal — gets inside a shell. The mollusk (an oyster or mussel) protects itself by building a special bag called a pearl sac around the intruder. Cells in that sac slowly cover the intruder with layers of a shiny material called nacre (the same stuff that makes the inside of the shell glossy).

Over months or years, these layers grow and form a pearl. Natural pearls are very rare because you must gather and open hundreds of shells to find even one pearl. Inside, a pearl often shows a darker center and a shiny outer layer when it is cut in half.

People can learn whether a pearl is natural, cultured, or imitation in a few ways. If you gently rub two pearls together, real pearls (natural or cultured) feel slightly gritty because of tiny nacre platelets, while imitation pearls feel smooth. A microscope lets experts see the tiny platelets or a smooth coating up close.

To be certain, gem labs use an X-ray to look inside a pearl. An X-ray shows whether there is a bead nucleus, a central cavity, or concentric growth rings. Only a well-equipped lab can tell natural and cultured pearls apart for sure.

Imitation pearls are made to look like real pearls but are not formed by a living mollusk. Some are carved from pieces of shell such as mother-of-pearl, coral, or conch shell. Others are glass or plastic beads coated with a shiny paint called essence d’Orient to give a pearl-like shine.

Imitation pearls can look very pretty and are much cheaper. They often feel completely smooth and may be lighter in weight. Because they are made by people, they do not have the thin nacre platelets that real pearls have.

Freshwater pearls grow in mussels that live in lakes, rivers, and ponds. Many of the pearls you see today come from farms in places like China, where people care for mussels and help pearls grow. They often make many shapes and can be colorful.

Saltwater pearls come from oysters that live in the sea, such as in lagoons or around small islands called atolls. These oysters are a different family from freshwater mussels. Both freshwater and saltwater pearls can be shiny and beautiful, but they come from different animals and environments and sometimes look different in shape, size, and color.

A cultured pearl is made when people help start the pearl-making process. A tiny piece of mantle tissue from another mollusk — called a mantle tissue graft — or sometimes a round bead is placed inside a host shell. That makes a pearl sac form, and the mollusk begins to lay down layers of nacre around the graft or bead.

There are two common ways: saltwater farms usually use a bead nucleus to make round pearls, while many freshwater farms grow pearls without beads using mantle tissue alone. Cultured pearls grow the same shiny layers as natural pearls, but they begin with human help.

When people help oysters or mussels make pearls, the result is called a cultured pearl. Farmers put a tiny bead or a small piece of tissue into the shell to start a pearl. Normally the pearl grows in a round shape around that bead.

Sometimes the pearl grows in a different way and becomes a keshi pearl. A keshi is made entirely of nacre, the shiny material that makes pearls glow. Keshi pearls are often small and oddly shaped because the bead slipped or was not used. Pearl farmers usually try to avoid keshi, but sometimes they put shells back into the water so a new keshi pearl will grow on purpose.

A natural pearl forms without people starting it. Long ago, people found natural pearls in places like the Persian Gulf near Bahrain. Today, a few pearl boats and divers still search for natural pearls in waters such as around Australia.

Natural and some rare cultured pearls are especially valuable because they are uncommon. South Sea pearls come from a big oyster called Pinctada maxima and are the largest and most prized cultured pearls. Black pearls from Pinctada margaritifera are different and not South Sea pearls. Experts use X-rays to check if a pearl is truly natural, because one oyster usually makes only one big pearl at a time, which keeps them rare.