The most colorful of all pearl-producing mollusks isHaliotis rufescens, more commonly known as the red abalone. An array of opal-like iridescent colors races across the shell, both inside and out. Of course, the more important iridescence is inside the shell-the “mother-of-pearl,” which dictates the color of the pearl. But unlike most pearl-producing mollusks, the abalone has only one shell.

Abalone (pronounced AB-uh-LO-nee) is a univalve mollusk that bears more resemblance to a giant snail than an oyster. The mollusk slides along the sea floor, using its colorful shell as a protective roof. Abalone pearls are created by the mollusk in the same manner as those of other oysters, but because of its one-shell structure, the pearls are both rare and unusually shaped.

History and romance. Natural abalone pearls are found from Baja California (the Mexican peninsula’s coast just south of San Diego) north to the Alaskan coastline. American abalone pearls are a rare find: Only one quality pearl is found in approximately every 50,000 mussels. The reason for that can be found at the nearest raw bar. Since abalone is harvested more for dinner than for decoration, the probability of the mollusk having time to grow a pearl-five to 10 years-is slim. (Although it’s considered a delicacy, abalone meat is fairly chewy. It’s best prepared by slicing thinly against the grain, pounding with a tenderizer, and quickly sautéing in a hot pan. It also may be eaten raw as sushi.)

Unfortunately for its aficionados, the California abalone population is dwindling, making collecting even more of a challenge. In fact, since 1997, when the California Fish and Game Department banned all commercial fishing of abalone, only sport fishermen have been permitted to harvest California abalone pearls. And with a daily sport limit of just four shells, serious collectors must buy from California sport fishermen, Mexican commercial harvesters, and those fishing north of the California border.

Other abalone varieties with pearls are found along the coasts of Australia, Japan, Korea, New Zealand, South Africa, and Thailand. The size of the pearls is different in each variety. The red abalone is one of the larger shells and produces the California pearls.

Color variations. The opalescent rainbow colors of blue, green, yellow, orange, and red are all commonly seen on the abalone pearl. There are purplish-magentas as well as silver-pinks and golds, bronzes and silvers, all of which can be combined on just one pearl.

Qualities. Besides color, the qualities of abalone pearls include luster, presence or absence of blemishes, and overall shape. Nacre thickness isn’t an issue, since natural pearls are almost all nacre. (Much of what is seen in the market are abalone mabés, which are not natural pearls but cultured blister pearls, which are then hollowed out and filled with glue.) Natural abalone pearls are mostly baroque and commonly have tooth- or horn-like outlines. Because of their free-form nature, they can also be either solid or hollow.

Unlike Japanese cultured pearls, abalones may experience a greater fluctuation in water temperature, which can determine the layering of the nacre and conchiolin (an organic binding agent), and therefore the intensity of the pearl’s colors. In the winter months, the mollusk lays down a protective conchiolin layer; in the summer, smooth iridescent nacre is produced, and a gemstone is created. This is similar to the production of South Seas and Tahitian pearls, in which the thick nacreous layers occur during the summer months and warmer temperatures. It’s opposite to the Japanese culturing process, in which the nacreous layers are best laid down during the winter months when colder waters cause the mollusk to create thin layers of nacre, generating a finer luster.

Value. There are basically two types of wild natural abalone pearls: loose pearl, which is formed in the gonad/stomach area and is commonly horn-like or tooth-like in appearance; and blister pearl, which is attached to the inner shell where the parasite has been covered by the mother-of-pearl. While a collector is more likely to find a blister pearl, abalone pearls that are loose and of a marketable shape are more rare and valuable.

Color affects value as well. Pearls that display shades of pink, blue, and green are considered by many to be the most sought after and pricey.

The latest prices. Fine- to gem-quality natural abalone pearls can cost anywhere between $200 and $2,000 per carat. Pearls of smaller sizes and more moderate qualities are available for much less. Blister pearls typically sell by the piece and can be priced anywhere from $10 to $20 up to $300 or $400 each.

Enhancements and culturing. No enhancements are made to abalone pearls. While there have been attempts to culture abalone pearls, there are virtually no commercially cultured abalone pearls available. The problem lies in the fact that the redHaliotis is a bleeder, making it extremely difficult to keep the mollusk alive after cutting it open to insert a bead. And because the mollusk is constantly moving along the rocks looking for food, the insertion is more than likely to fall out even if the animal lives long enough to accept the bead. Mabé pearls, however,are being cultured. It is relatively easy to stick the half bead to the inner shell, allowing the mollusk to lay down mother-of-pearl nacre over the intruder and create a cultured blister pearl.

Care and cleaning. Generally speaking, the pearls are cleaned before being sent to a retail jeweler. However, if you find one through a sport fisherman, you may have to do some cleaning yourself. Ocean pearls commonly exhibit salt residue and a certain degree of light oxidation that interferes with the luster of the pearl. You can usually remove the salt or oxidation by rolling the pearl in your palm with a small amount of salt and water. If that doesn’t do the trick, carefully use a bench polisher buffing wheel to gently remove the build-up.

Because the pearls are very large, they harbor a lot of protein in the form of the conchiolin binding agent that holds the nacreous crystals. If this becomes dry, the pearl will begin to disintegrate. Soaking the pearl in ocean salt water or a similar solution should rehydrate the protein. Although pearls dislike being exposed to anything acidic or drying, they are fairly durable. A pearl can spend many years in a dry environment-e.g., a vault-before it begins to deteriorate.

Bench settings and precautions. Few precautions are necessary, as most abalone pearls are bench friendly. They hold up well under both steam and ultrasonic treatments.

Recommended reading. For more information on abalone pearls, see the following:Pearls (Fred Ward Gem Book Series) by Fred Ward (Gem Book Publishing, revised edition 1998).

GIA’s Pearls course, GIA, Carlsbad, Calif.

Special thanks to Cory Smith of Brilyse Pearls, Santa Cruz, Calif; Fred Ward, Bethesda, Md.; and Tish and Wes Rankin of Pacific Coast Pearls, Petaluma, Calif.