A pearl is a hard, rounded object that grows inside the soft tissue of a living mollusk, usually an oyster or a freshwater mussel. Most pearls sold today are cultured, meaning a farmer started the process by hand, while natural pearls form without any human help and are now rare.
How a pearl forms
A pearl starts when cells from the mollusk's mantle, the tissue that builds the shell, end up inside the animal's body. Those cells form a pouch called a pearl sac and coat whatever sits inside it with the same material that lines the shell. The popular grain-of-sand story is mostly a myth.
The coating in most gem pearls is nacre, a stack of microscopic aragonite plates held together by an organic protein. The page on what pearls are made of explains how that layered structure produces luster and the soft rainbow sheen called orient. Pearls from some sea snails, such as the conch pearl, have no nacre and show a porcelain-like surface instead.
Natural and cultured pearls
Natural pearls were harvested for thousands of years from beds in the Persian Gulf, the Gulf of Mannar, the Red Sea and the coasts of the Americas. Divers opened huge numbers of oysters to find a few pearls. The story of Bahrain and the Persian Gulf shows how a whole regional economy rose and fell on pearl diving.
Cultured pearls took over the market in the 20th century after Japanese researchers, with Kokichi Mikimoto the best known, worked out how to start pearls on purpose. A technician inserts a shell bead and a small piece of donor mantle tissue, or tissue alone, and returns the mollusk to the water for months or years. A cultured pearl is a real pearl made by a real animal. Labs use X-ray imaging to tell it from a natural pearl.
The main types of cultured pearl
Four groups make up most of the trade:
- Akoya pearls come from the small Pinctada fucata oyster, farmed mostly in Japan and China. They are classically round, white to cream, and often 6 to 8 mm.
- South Sea pearls grow in the large Pinctada maxima oyster off Australia, Indonesia and the Philippines. South Sea pearl farming yields white, silver and golden pearls from about 9 mm to over 15 mm.
- Tahitian pearls come from the black-lip oyster, Pinctada margaritifera, in French Polynesia. Tahitian pearl farms produce naturally dark grays, greens and the purple-green blend sold as peacock.
- Freshwater pearls grow in mussels, with Chinese pearl farming responsible for most of the world's supply. They come in white, pink, peach and lavender.
How pearls are judged
There is no single worldwide grading standard. Gemologists look at size, shape, color, luster, surface quality, nacre quality and, for strands, matching. The full guide to pearl grading covers the A to AAA and Tahitian A to D systems and their limits.
See the birthstones by month list and traditional anniversary gifts for more.
Caring for pearls
Pearls rank only about 2.5 to 4.5 on the Mohs hardness scale, and acids, perfume, hairspray and cosmetics can dull nacre. Put pearls on after makeup and take them off first. Wipe them with a soft, damp cloth and store them apart from harder gems. Never use an ultrasonic or steam cleaner. Have a strand that gets frequent wear restrung every year or two. The guide to cleaning jewelry safely covers pearls alongside other soft and organic gems.
Frequently asked questions
Are cultured pearls real pearls?
Yes. A mollusk grows a cultured pearl the same way it grows a natural one. The only difference is that a person started the process, and trade rules require the word "cultured" in the description.
What is the most expensive type of pearl?
Fine natural pearls with good size and luster bring the highest prices. Among cultured pearls, large, round South Sea and Tahitian pearls generally cost more than Akoya or freshwater pearls of similar quality.
How can you tell a real pearl from a fake?
Rub a pearl gently against the edge of your front tooth. Real pearls usually feel slightly gritty because of their nacre plates, while glass and plastic imitations feel smooth. A lab test is the only way to confirm natural or cultured origin.