Pearl, the birthstone for June, is among the most timeless, classic and treasured of all gems. Throughout history, these noble gems have been associated with wisdom, wealth, purity, romance and mystery. The ancient Egyptians were buried with them. In Rome, pearls were considered the ultimate symbol of wealth and status. The Greeks prized them for their beauty and association with love and marriage. Medieval knights wore them in battle as a talisman against injury. And during the Renaissance, some European countries banned all but nobility from the right to wear them.

It's hard to believe that such a luscious, beautiful gem comes from such humble origins. A natural

pearl starts out as a grain of sand or microscopic worm that works its way into an oyster and cannot be expelled. To protect its soft body from this irritant, the oyster secretes a smooth, hard crystalline substance called nacre. Layer upon layer of nacre coats the foreign object and hardens, ultimately forming a pearl. In general, the thicker the nacre, the richer the "glow" of the pearl - which can greatly enhance its value.

Although early pearl gathering depended on divers braving the oceans' depths to retrieve these treasures, the vast majority of pearls today are grown, or cultured, on pearl farms by surgically inserting a small shell bead, or nucleus, into the mantle of an oyster.

Even though pearls are harvested en masse on pearl farms, producing a quality pearl is an extremely rare event. It is estimated that half of all nucleated oysters do not survive - and of those that do, only 20% bear marketable pearls.

Pearls - the recommended gift for couples celebrating their third and 30th wedding anniversaries - are cultured in a variety of sizes, shapes, colors and kinds: