It's said that if diamonds are a girl's best friend, then pearls must be her favorite sister. This lustrous gemstone is one of the June birthstones.

The pearl is an organic gem grown within oysters and a few other mollusks. It is formed when a foreign object, like a tiny stone, makes its way into the mollusk's shell. The irritation caused by the foreign particle makes the oyster form a secretion, called nacre, to cover it. Nacre is the same material that forms the mollusk's shell.

Freshwater pearl shapes vary greatly and include corn, potato, teardrop, rice/oval, and almost round or roundish. Saltwater pearls are commonly known as Oriental pearls and those produced by freshwater mollusks are called freshwater pearls.

Pearls occur naturally in a spectacular array of colors, ranging from white to gold, purple and black. A pearl's color depends on both the species of mollusk that produced the pearl and the environment in which the animal lived. Pearls are extremely porous, so they readily accept dyes. Dyes can be used to produce any pearl color. Irradiation darkens the nucleus to produce darker pearls, like blues, grays and blacks. Metallic pearl colors are often gamma ray irradiated as well. As a rule of thumb, all bright or striking pearl colors are dyed and/or enhanced.

A great irony of pearl history is that the least expensive cultured pearl product in the market today rivals the quality of the most expensive natural pearls ever found.

Pearls are less durable than most gems, and are sensitive to acids, dryness and extreme humidity. Therefore, they should be cared for accordingly:

• If you wear cosmetics, perfume or hair spray, apply them before putting on your pearl jewelry.
• When taking off your pearls, wipe them with a dry, lint-free cloth. The calcium carbonate in pearls dissolves in human sweat or oil from the skin, and this will diminish the pearls' luster.
• Be sure they don't get exposed for a long time to direct sunlight, especially ultraviolet rays; the protein in pearls becomes yellow under sunlight.
• If your pearls need cleaning, do so with warm soapy water (never an ultrasonic cleaner), taking care not to get water into the drill hole as the pearl may discolor.
• Dry your pearls flat on an absorbent, soft (and preferably lint-free) towel.
• Store them away from contact with metals or harder stones that might damage them. Also, don't store them in plastic, as it will seal out air, thereby accelerating deterioration.