On the nature of moonstones
Moonstone is a variety of the mineral orthoclase. (Orthoclase is a member of the feldspar family.) Moonstones are made up of microscopic layers, not only of othoclase but also another related mineral called albite. When light is caught between these layers, it appears to billow across the gemstone like moonlight -- this is effect is known as adularescence.
In fact, adularescence is a more important factor than the mineral's actual identity... other minerals in the feldspar family also exhibit adularescence and they are also know as moonstones! For example, the gemstone known as rainbow moonstone is actually a variety of labradorite, not orthoclase.
On finding moonstones and what to look for
Should you wish to go hunting for moonstones in nature, you can start here in North Carolina. But you will have to gather your passport and traveling gear if you want to find truly gem-quality moonstones. India, Madagascar, Tanzania, and Sri Lanka are the major sources of moonstones on the market today. Historically, Switzerland was among the first sources of fine-quality moonstone.
Moonstones, like most gemstones, are evaluated according their color, clarity, cut, and carat weight.
Color: Although extremely rare today, moonstones with a deep blue, almost electric, sheen are considered the finest specimens. But you can also find moonstones in a variety of hues such as green, peach, brown, and gray with blue, silver, white or rainbow adularescence.
Clarity: Inclusions in moonstones are known as centipedes. Sometimes these inclusions can add interest to the gemstone but generally a stone that is nearly transparent and free from inclusions is preferred. A degree of translucency (light is diffused) will accentuate the adularescence.
Cut: Moonstones have almost always been cut in cabochons. The smooth surface reveals the inner mystical light of the stone. But faceted moonstones are being used more and more by custom jewelers in their designs.
Carat: Large moonstones of gem quality are very rare, therefore they are more valuable.
On the romance of the moonstone (or interesting tidbits)
- Aids in prophesy. Hold a moonstone in your mouth during a full moon to see the future or place beneath your pillow to dream of what is to come.
- A magic moonstone. In the fifteenth century, Pope Leo X claimed to be in possession of a moonstone which he said waxed and waned in brilliance with the phases of the moon.
- Prevents moonstroke. Old European beliefs held that moonstones could cure fever, inspire passion, ward off moonstroke (selenoplexia), and prevent lunacy.
- Solidified moonbeams. According to Hindu legend, moonstones were fragments of solidified moonbeams that reached the earth and were very lucky talismans.
- Cat's eye. Some moonstones display a cat's eye effect, also known as chatoyancy. Even rarer are those that exhibit four-rayed stars (asterism).
- Art Nouveau era. Moonstones were often used by the great artists of the Art Nouveau era. René Lalique's jewelry designs often featured this shimmering stone. During the Arts and Crafts period in the latter half of the nineteenth century, artisans often used moonstone in handcrafted silver pieces.