Moonstone Buying Guide
With a mysterious sheen reminiscent of moonlight, moonstone has been treasured for thousands of years. This effect, called adularescence, is caused by fine layering of feldspar minerals, which catch the light and shimmer below the gem’s surface. Due to its use as a birthstone for those born on Mondays or as an alternative to pearl and alexandrite for June births, this gem has recently gained popularity. Still, prices are low for all but the top-quality moonstones, and moonstone buying is fairly straightforward. Nevertheless, be wary of simulants and keep in mind the material’s softness when choosing a jewelry setting.
Moonstone Buying and the Four Cs
Moonstone color can be separated into body color and adularescence (sheen) color. Ideally, moonstones exhibit a transparent, colorless body with pure blue, medium-toned sheen.
However, this feldspar can occur in many colors. Any body color detracts from the value, and unattractive green hues will significantly lower the gem’s price. Peach pink hues are popular, but not as highly regarded as colorless stones. Brown, yellow, and blue hues also occur.
Adularescence can also occur in many colors. “Rainbow moonstones” from India exhibit a multi-hued sheen, often blue and yellow. White is another popular sheen, though not as valuable as blue.
To best display adularescence, moonstones are cut in a high cabochon. Those with a flatter cut won’t exhibit as much sheen. Gem cutters fashion other gems into beads or facet them for greater brilliance.
Carved moonstones are popular, but some carvings hide inclusions or fractures in the stone, or reduce the adularescence. However, well-carved specimens are simply mesmerizing.
Moonstones below one carat are readily available. Fine specimens over five carats are rare, and the price per carat doubles. Prices double again at the ten-carat mark due to increased rarity.
Although a popular gem, moonstones are relatively soft, sitting at only 6-6.5 on the Moh’s scale. They are also susceptible to chipping. Therefore, protective jewelry settings or use in pendants or earrings are recommended to keep the stone from damage.
Treatments and Simulants
Though uncommon, a treatment that impregnates moonstones with an organic substance has been found by the Gemological Institute of America (GIA). This procedure improves adularescence. Under ultraviolet light, these specimens fluoresce.
You’ll more commonly find other materials used as moonstone simulants. Some unscrupulous sellers will offer leaded glass, opal, or labradorite as moonstone. The presence of caterpillar inclusions indicates a true moonstone, while swirls and bubbles present under magnification signal glass.