Button: A dome-shaped pearl with a flat bottom.

Choker: A pearl necklace that is 16 to 18 inches in length.

Circles: Concave, concentric rings on a pearl's surface.

Clean: Absence of blemishes on a pearl's surface.

Color: An evaluation of quality used to describe the color of a pearl.

Collar: A pearl necklace that is 10 to 13 inches in length.

Grafting: The insertion, through human intervention, of an irritant into the body or the mantle tissue of a mollusk, in order to produce a cultured pearl.

Lustre or Luster: The combination of surface shine and the depth of inner light refraction in a pearl. Lustre is one of the great determinants of a pearl's quality.

Mantle Tissue: The layer of thin tissue adhering a mollusk to its inner shell.

Matching: Using luster, surface, shape, color and size to match one pearl with another to create a piece of pearl jewelry, such as a necklace.

Matinee: A pearl necklace that is 20 to 24 inches in length.

Millimeter: The metric measurement used to determine the size of a pearl. One mm equals 1/25 of an inch.

Momme: The weight measurement for pearls in Japan. One momme equals 3.75 grams, or 18.7 carats.

Nacre: A calcium carbonate-based crystalline substance secreted by a mollusk as a defensive device against the intrusion of a foreign irritant into its body.

Nucleus: A small bit of polished shell from an American freshwater mollusk used as an irritant and inserted into the body of a saltwater mollusk. By the same token, a small bit of soft mantle tissue from one freshwater mussel is inserted as an irritant into the body of another freshwater mollusk.

Nucleation: Also called grafting or implementation, this is the process of inserting an irritating nucleus into the body of a mollusk so that it will secrete nacre to cover it, consequently producing a cultured pearl.

Opera: A pearl necklace that is 28 to 32 inches in length.

Princess: A pearl necklace that is 17 to 19 inches in length.

Rope: A pearl necklace over 45 inches in length.

Shape: A quality evaluation, describing the shape of a pearl. Round is the most prized shape in the industry, but saltwater and freshwater pearls are produced in a variety of shapes, just as they exhibit a variety of colors.

Size: The diameter of a pearl measured in millimeters and used as a quality and price evaluation of the pearl.

Sorting: Separating pearls by surface, shape, color and size prior to the jewelry matching process.

Surface: A quality evaluation of the amount of blemishes on a pearl, ranging from clean to heavily blemished.

Gold-Lip Oyster: The large oyster found in the waters off Australia, Indonesia, Philippines and Japan, which produces gold-colored South Sea Pearls.

Pinctada Fucata: The industry term for the saltwater mollusk that produces Akoya cultured pearls.

Pinctada Maxima: The industry term for the White-lip oyster that produces South Sea Pearls.

Pinctada Margaritifera: The industry term for the saltwater mollusks that produces Tahitian cultured pearls.

Uniondae Hyriopsis Schlegeli: The freshwater mussel, prevalent in China, which produces a strong pearl with thick nacre and a bright luster. Its pearls come in a palette of colors ranging through plum, lavender, peach, apricot, curry, red pepper, cinnamon, celery and sage.

White-Lip Oyster: Large oysters found in the waters around Australia, Indonesia, the Philippines and Japan, and producing good-sized South Sea cultured pearls whose tints include silver-white, pink and cream.

Akoya Cultured Pearls: Pearls produced by deliberate human intervention in several varieties of saltwater mollusks generally found in the waters around Japan and China. The Akoya pearl ranges in color from cream, white, rose, gold and blue-gray, and remains justly famous in the hierarchy of cultured pearls for its spectacular luster and beauty.

Baroque: A cultured pearl that is asymmetrical and free form in shape.

Biwa Pearl: A cultured pearl cultivated in a freshwater mussel in Lake Biwa, in Japan. Recently, the term has been allowed to refer to any pearl cultivated in a freshwater mussel in Japan.

Conch Pearl: Similar in color to pink coral, these pearls are produced by a conch, which is a saltwater mollusk from tropical waters.

Cultured Pearl (also "Cultivated Pearl"): A pearl grown in a mollusk that has been surgically implanted with an irritant, through human intervention.

Freshwater Cultured Pearl: A cultured pearl cultivated in a freshwater mollusk from a lake, river or pond.

Imitation Pearl: Man- or machine-made pearls.

Keshii Pearl: Also known as a Seed Pearl. It is a non-nucleated pearl produced accidentally as a by-product of the cultivating process, and consequently not considered a natural pearl.

Mabe Pearl: A dome-shaped cultured pearl cultivated on the inner shell of a mollusk rather than in its body.

South Sea Cultured Pearl: Ranging in hues of white, gold, silver, cream and champagne, these cultured pearls are quite large and are cultivated in the white-lip oyster.

Tahitian Cultured Pearl: Cultured pearls cultivated in the black-lip oyster found in French Polynesia, and producing pearls in natural tints of black, silver, gray, green, orange, gold, blue and purple.

From the Latin word "perula," or small pear, the pearl has been cherished throughout history.  Numerous legends exist to explain its mysterious presence, such as the Persian belief that these gems are formed when a rainbow meets the earth.  Pearls have also been said to have been born of a lake created by the tears of Adam and Eve, or sprung from the tears of mermaids or angels. The story might vary, but all seem to be in agreement that the pearl is one of the earth's most magnificent and valuable treasures. Long considered to be more appropriate for nobility than common folk, they were even thought to have the magical power to bring wealth and longevity to the wearer.

More than any other gem, pearls have been used for their medicinal effects.  In ancient China, they were swallowed whole as a cure for fever, hemorrhage and eye diseases.  Since their composition is primarily calcium carbonate, lower grade pearls continue to be used in many cultures as an antacid medication or dietary supplement.  Some even use pearls as a love potion!

Most of the pearls sold today are cultured pearls, a combination of both man and nature's efforts.  This is because only about one in 10,000 pearl oysters contain a natural pearl of gem quality, making natural pearls relatively difficult to come by.  The Chinese were the first to attempt the process of culturing pearls, but today these gems are cultivated in both fresh and sea waters throughout the earth.  Although most people think of pearls as white, they come in a variety of other colors, from red to black.

Pearls are equally appropriate at home, at work, or an evening out.  They have been found among the jewels of the likes of Mary Queen of Scots, Queen Elizabeth I of England, and Marilyn Monroe.  But you don't have to be rich or famous to wear a strand of these lustrous gems.  Subtle and simple, yet elegant, they are as suitable for a teenaged girl as for a queen.

For information on other birthstones, check out About Birthstones.

The size of the oyster directly affects the size of the pearl it creates. Larger mollusks, for instance, create larger pearls.

However, large cultured pearls require a larger nucleus to be implanted into the oyster -- which increases the chance of the mollusk either rejecting the nucleus, or dying before a pearl has an opportunity to develop.

A large nucleus also affects the complexion of the pearl. It's more likely that a larger, mature pearl will be formed with greater surface defects.

Round pearls are measured according to their diameter, while baroque pearls are measured by their length and width. Size is determined by diameter and expressed in millimeters, since pearls are sold by the millimeter.

Pearls, of course, come in a range of sizes, these being the average:

• Akoya: 6 to 8 millimeters in diameter, with 8 mm considered large.
• Freshwater: 5 to 6.5 millimeters, for the best quality.
• South Sea: 11 and 13 millimeters, large by any pearl standard.
• Tahitian: The match of the South Sea pearl, also between 11 and 12 millimeters.

Pearl strands are sorted by size, with a specific millimeter range:

• Petite: 6 millimeters and below.
• Classic: 6 to 7.5 millimeters.
• Most Popular: 7 to 7.5 millimeters.
• Outstanding: 8 millimeters.

A pearl's size doesn't necessarily indicate its quality, but it most certainly does affect its price. All things considered, the larger the pearl, the higher its value.

As a pearl is produced it can develop these marks, and surface quality is judged by the number of those flaws visible on the outside of the pearl. A pearl with fewer surface markings is more rare and hence more valuable. However, like diamonds, pearls are rarely flawless.

Fine pearls have virtually no spots, bumps, pits, circles or wrinkles. High luster will often make tiny surface imperfections less visible and generally compensate for these small imperfections. Also, when the pearls are strung as a necklace or mounted on earrings, the mounting and drill holes can do much to detract from any flaws inherent in the pearl.

Usually, one finds pearls ranging from "all round" to "mostly round." With Tahitian pearls, which are extremely rare and expensive when discovered in perfectly round form, the industry standard for the average Tahitian pearl is termed, "slightly off round."

Pearl Drops

Other shapes, of course, are valued. The drop pearl is particularly prized because its shape adapts naturally to earrings and pendants.

Baroque Pearls

Baroque pearls, whose shapes are symmetrical rather than round, can sometimes be amazingly lustrous and gorgeous.

Mabe Pearls

Mabe pearls look like half of a round pearl, and usually are mounted within a setting and a backing.

Other Pearl Shapes

Other, more asymmetrical shapes that enjoy a vogue among pearl lovers are oblong, pear-shaped and teardrop pearls.

Matching Pearls

Shape as well as size is an important factor when professionals string pearls. The goal is to match pearls in terms of size, color, luster, and surface marks to create a strand of pearls as uniform to the eye as possible.

The thicker the nacre, the more lustrous the pearl. Though there are exceptions to that rule, the amount of nacre determines the reflective quality of the pearl's surface. And luster is the most important factor determining the quality of a pearl. It is especially important that the surface be without blemish, because luster is more often seen on a smooth surface without ridges that deflect the light.

A low-luster pearl is dim and monochromatic, but a higher grade of pearl with thicker nacre produces a resilient pearl with far few surface blemishes. This creates a sharp, high-contrast surface that is almost mirror-like in its reflective qualities.

Colors generally range from cream, to silver-white, to black. But there are also color overtones reflected across a pearl's surface. In fact, the color of a pearl more often than not is a meld of its body color and its overtone, just as the term "white-rose" will describe a white pearl with a rosy-colored hue.

Akoya Pearls

Akoya cultured pearls are white lustrous pearls with usually cream or rosé colored overtones. These are the classic pearls most often used in pearl strands. Classic Japanese Akoya cultured pearls come in shades of white, the most valuable shades being rosé and white. The other shades are white-rose, silver-white rose, greenish-white rose, and greenish-white.

Freshwater Pearls

Freshwater pearls come in various pastel shades of white, pink, peach, lavender, plum, purple, and tangerine.

South Sea Pearls

South Sea cultured pearls come in shades of lustrous white, often with silver or rosé overtones. They are larger in size than the Akoya pearl and are also used in the creation of fine pearl strands and ropes.

Black Pearls

Black pearls are known as Tahitian pearls, and come most often in shades of black and gray. While a Tahitian pearl has a black body color, it will vary in its overtones, which most often will be green or pink. Tahitian cultured pearls differ from other pearls in one important respect. Yes, they are cultured, as opposed to natural -- but their black color is naturally produced by the oyster, which makes them "naturally black" cultured pearls.