Pearl, Alexandrite, Moonstone
Perhaps the best-loved gems of all time, pearls—both natural and modern cultured pearls—occur in a wide variety of colors. The most familiar colors are white and cream (a light yellowish brown). Black, gray, and silver are also fairly common, but the palette of pearl colors extends to every hue. The main color, or bodycolor, is often modified by additional colors called overtones, which are typically pink (sometimes called rosé), green, purple, or blue. Some pearls also show the iridescent phenomenon known as orient.
Cultured pearls are popular for bead necklaces and bracelets, or mounted in solitaires, pairs, or clusters for use in earrings, rings, and pendants. Larger pearls with unusual shapes are popular with creative jewelry designers.
Pearl—natural or cultured—is a US birthstone for June, together with alexandrite and moonstone. Natural pearls form in the bodies, or mantle tissue, of certain mollusks, usually around a microscopic irritant, and always without human help of any kind. The growth of cultured pearls requires human intervention and care. Today, most of the mollusks used in the culturing process are raised specifically for that purpose, although some wild mollusks are still collected and used.
To begin the process, a skilled technician takes mantle tissue from a sacrificed mollusk of the same species and inserts a shell bead along with a small piece of mantle tissue into a host mollusk’s gonad, or several pieces of mantle tissue without beads into a host mollusk’s mantle. If a bead is used, the mantle tissue grows and forms a sac around it and secretes nacre inward and onto the bead to eventually form a cultured pearl. If no bead is used, nacre forms around the individual implanted mantle tissue pieces. Workers tend the mollusks until the cultured pearls are harvested.
There are four major types of cultured whole pearls:
Akoya—This type is most familiar to many jewelry customers. Japan and China both produce saltwater akoya cultured pearls.
South Sea—Australia, Indonesia, and the Philippines are leading sources of these saltwater cultured pearls.
Tahitian—Cultivated primarily around the islands ofFrench Polynesia (the most familiar of these is Tahiti), these saltwater cultured pearls usually range from white to black.
Freshwater—These are usually cultured in freshwater lakes and ponds. They’re produced in a wide range of sizes, shapes, and colors.
Pearls should never be cleaned in an ultrasonic or steamcleaner. It’s safe to use warm, soapy water for occasional, thorough cleaning. If the pearls are strung, be sure the string is completely dry before wearing. For routine care, it’s best to wipe cultured pearls with a very soft, clean cloth after each wearing.
Alexandrite, with its chameleon-like qualities, is a rare variety of the mineral chrysoberyl. Its color can be a lovely green in daylight or fluorescent light, changing to brownish or purplish red in the incandescent light from a lamp or candle flame. This is a result of the complex way the mineral absorbs light. Alexandrite’s dramatic color change is sometimes described as “emerald by day, ruby by night.” Other gems also change color in response to a light-source change, but this gem’s transformation is so striking that the phenomenon itself is often called “the alexandrite effect.”
Alexandrite is also a strongly pleochroic gem, which means it can show different colors when viewed from different directions. Typically, its three pleochroic colors are green, orange, and purple-red. However, the striking color change doesn’t arise from the gem’s pleochroism, but rather from the mineral’s unusual light-absorbing properties. Because of its scarcity, especially in larger sizes, alexandrite is a relatively expensive member of the chrysoberyl family. It shares its status as a June birthstone with cultured pearl and moonstone.
The third birthstone for June is the Moonstone. It was given its name by the Roman natural historian Pliny, who wrote that moonstone’s appearance altered with the phases of the moon — a belief that held until well after the sixteenth century. A phenomenal gemstone, moonstones show a floating play of light (called adularescence) and sometimes show either a multirayed star or a cat’s eye. Considered a sacred stone in India, moonstones often are displayed on a background of yellow (a sacred color) and are believed to encapsulate within the stone a spirit whose purpose is to bring good fortune. Part of the family of mineralscalled feldspar, moonstone occurs in many igneous and metamorphic rocks and comes in a variety of colors such as green, blue, peach, and champagne. The most prized moonstones are from Sri Lanka; India, Australia, the United States, Mayanmar, and Madagascar are also sources.