Tips: Selecting Pearls

The beauty of pearls have been admired throughout history and all across the world.

There are pearls in shapes, colors and range of costs for every taste and budget. In general, the more expensive pearls have a higher degree of luster, smoother surfaces, thicker nacre and larger size. Pearls are cultivated in many parts of the world today, however, Akoya pearls were the earliest cultured pearls; they are known for their deep luster and smooth, round shape. Japan developed the perliculture industry in the early 1900’s and remains a world-leader in the supply and variety of pearls.

Very few single-shell mollusks (called gastropods) actually produce pearls; pearls mostly come from two-shelled or bi-valve mollusks. The oldest known fossil pearls date back around 230 million years (American Museum Natural of History) and appear mostly in marine mollusks; these are very rare finds usually preserved by clay layers.

Pearls grow concentrically around a nucleus or foreign body which is usually manually introduced into the oyster at specific stages of growth and maturity. Certain types of mussels take 3 years to become mature enough to develop a pearl. In natural oysters, a grain of sand is the natural “irritant” that causes the oyster to develop a layer of calcium carbonate around the foreign object that has found it’s way inside the shell. Alternating layers of conchiolin (a natural protein secreted by the oyster to cover irritants) and calcium carbonate “harden” to form nacre. In cultured pearls, typically a small “bead” is placed inside the oyster or mussel shell along with a small piece of mantle tissue to create a pearl. It can take up to 3 years for a pearl to grow and the majority of oysters and mollusks grown do not yield a high-quality pearl. The pearl farming industry (perliculture industry)uses a complex series of steps that create specialized growth and development environments for pearls. It is often difficult to tell the difference between a natural or cultured pearl; price is often an indicator as natural pearls are far more rare and, if they are of high quality, may cost hundreds of dollars per pearl. Very high quality Akoya pearls may cost thousands of dollars for a single necklace; and larger pearl strands are sold for between $20,000 to $40,000.

Most pearl farms grow multiple pearls in each oyster or freshwater mussel. Akoya pearl oysters are typically grown with about 5 pearls in each oyster, while mussels often have anywhere from 40 to 60 nucleus fragments embedded (implanted) into each shell, yielding the same number of pearls when grown. The nacre consists of tiny aragonite crystals which form in platelets creating the beautiful nacre that is highly lustreous and has been prized in pearls throughout history. Most pearl farms today use a high degree of environmental care for their oysters which includes cleaning the shells to prevent infection, inspecting them and having nutrient-rich water for optimal growth.

There are many variations in the quality of freshwater pearls today, the price will depend upon the overall size of each pearl, thickness of the nacre (skin/shell), and luster. Deep black pearls found almost exclusively in waters around Tahiti are also some of the most expensive pearls found today; the more perfectly round, lustreous and smooth; the more expensive they are. Natural & freshwater pearls normally are found in the following colors: white, peach, cream, blue, grey, and black. Pearls today come in many shapes and colors including: round, baroque, rice-shaped, button (round on one side with flat base), potato (round but not smooth), biwa (long needle-like shape), oval and coin-shaped. Some pearls are even grown in heart shapes and many are dyed to match fashion trends: red, green, peacock blue, orange and purple and many iridescent colors too.

See the photos below which illustrate the differences in quality of a few sample pearls:

High-quality Tahitian pearls

Dyed lower-quality “potato” pearls

Low-quality natural color coin pearls

TYPES OF PEARL

Freshwater Pearls: Grown in Japan, China & U.S.A. These pearls have a very wide range of size, shape, color, nacre and luster.

Tahitian Pearls: Mostly black pearls from the Black-lipped oyster of Tahiti. These are mainly large, round pearls ranging in size from 9 to 12 mm, and are considered to be some of the most rare pearls available. See photo above.

South Sea Pearls: Mostly saltwater pearls grown in areas of Australia, The Phillipines. These are very large, round pearls although often not perfectly round.

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LUSTER

NACRE

SIZE

SHAPE

COLOR

GLASS PEARLS

More Information About Pearls

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Gem photo credits: Most of the photos of gemstones and minerals shown here are reproduced with kind permission of Roger Weller, Professor of Geology at Cochise College, AZ. Mr. Weller has many more beautiful photos of gemstones, minerals and rock examples. The Cochise College science and geology website is an excellent source of information for those that would like to learn more about the wonderful treasures and geologic evolution of the planet we live on.