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Moonstone (Orthoclase Feldspar)

Jewel of the Month
By Gary Roskin, G.G., FGA, Senior Editor
This story appears in the November 2003 issue of JCK magazine
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This month’s jewel is displayed in finished jewelry created by award-winning designer Henry Dunay, New York. His mango-green moonstone pendant places 131 cts. of gems horizontally for a classic yet bold pendant, bezel-set in 18k yellow gold, with matching ring. Dunay mounts the gems over the yellow gold to create a golden yellow, honey-color moonstone sheen. Loose gems surrounding the Dunay pieces include a 40.32-ct. yellow-orange, carnelian color elongated oval; a 36.87-ct. bright orange oval; a 21.4-ct. deep gray; and two rainbow moonstones—one cabochon cut 11.48-ct. short oval, and one faceted checkerboard-top cushion weighing 9.82 cts. At bottom right is “Mr. Moonlight,” carved in classic white. Manu Nichani of Blue Moon Enterprise, Carlsbad, Calif., supplied all of the moonstones. For more information on Henry Dunay, call (800) 888-2525. To speak with Manu Nichani, call (760) 438-9237.

Only a few gem species exhibit a floating billowy light just under the polished surface, a phenomenon called adularescence. Mineralogists call gems with adularescence Adularia. Gemologists, jewelers, and lapidaries call them moonstones.

Moonstone is one of three phenomenal birthstones assigned to the month of June. The others are pearl (with its orient) and alexandrite (with its change-of-color).

Origin and legend. Most moonstones come from India. Although they’re found in small quantities all over the world, Burma is the only other important commercial source. Sri Lanka used to be on the “important” list, but sources say most commercial deposits there are played out. And while there seems to be plenty of Burma moonstone in the market, it’s believed that most of those goods are actually Indian moonstones that have been labeled with the more exotic “Burma” name to increase their desirability.

One interesting note: The gem’s other name comes from a deposit nowhere near the two major commercial deposits. The word “adularescence” comes from the locality where the mineral species orthoclase was discovered—the Adula mountain range, also called the Adula Alps, between southeastern Switzerland and Italy.

The name “moonstone” is reputed to have originated in India, because of the bluish billowy sheen resembling moonlight on the water in that country. It was once thought that moonstones were washed up on shore after a full moon and high tide, and some say this may be where the phrase “once in a blue moon” originated. And because of moonstone’s mysterious ghostly light from within, many in the East believe a spirit is locked inside the gem, making it a lucky charm with the properties of a crystal ball. Those who wear moonstones are said to be able to gaze into the future.

Just a little mineralogy. Moonstone is mineralogically complex, because it’s a variety within the feldspar mineral group. The key question about moonstone is, To which species of feldspar does it belong?

The feldspar group is made up of a number of species such as orthoclase, sanadine, oligoclase, microcline, and labradorite, to name just a few. These species include gems with common varietal names—sunstone, labradorite, spectralite, and amazonite.

Moonstone—either the orthoclase, sanadine, or oligoclase feldspar—gets its billowy sheen from light scattering off layered inclusions of yet another feldspar, albite. Rainbow moonstones, those that not only have a billowy adularescence but also an opal-like iridescence, are a combination of orthoclase and labradorite feldspars. Blue moonstone (see “Jewel of the Month,” JCK, September 2001, p. 91), which shows adularescence from reflections off growth planes, is strictly labradorite feldspar. This gem is considered by some not a moonstone, simply because its phenomenon is not caused by albite inclusions.

Qualities. The higher-quality moonstones are close to transparent and without visible inclusions. This quality in larger sizes is quite rare and becomes a big factor in stones larger than 10-mm x 12-mm ovals.

Numerous layers of inclusions causing white adularescence also make the gem less transparent, and inclusions are what cause the rainbow effect as well. Fewer inclusions mean fewer colors. On the other hand, fewer layers of inclusions not only increase transparency but also cause the adularescence to turn more bluish.

Oriented needles give moonstones chatoyancy—a cat’s-eye effect. Orthoclase moonstone can have a fairly sharp eye, and having both the adularescence and chatoyancy is rare in large sizes.

Color variations. Orthoclase moonstone typically is found in pastels of white, orange, brown, yellow, pink, very faint blue, very faint green, and gray. It ranges from translucent to semi-transparent and is cabochon cut to show off the adularescence.

Moonstone’s recent upsurge in popularity has boosted mining activity and inspired India to produce some new colors, including bright orange and carnelian. There’s also a new green called mango, named after the color of the unripened fruit.

Cutting and enhancement. Cabochon is the traditional cut for moonstone, since it allows for the adularescence and cat’s-eye effects. And because moonstone has two pronounced cleaving directions, faceting is usually not an option anyway. However, to bring out a flat surface sheen or broaden a rainbow effect, some cutters will make an attempt at faceting.

Other than cutting and polishing, we know of no enhancements used to alter the clarity or color of moonstone.

Pricing. Rainbow moonstones are priced the same or higher than blue moonstones, $45/ct.-$100/ct. for stones under 5 cts. and $100-plus/ct. for stones 5 cts. and larger.

White cat’s-eyes in larger sizes also can run $100/ct. Mango green is scarce in fine-quality large sizes and will be priced at $75/ct.-$80/ct. “Moonstone is a very good stone to work with,” says award-winning jewelry designer Henry Dunay, New York. “It’s not yet at the point where the prices have gone through the roof.”

Moon faces, when they were first introduced, were superbly carved by German gem artists—and priced accordingly. Now that moon faces have become so popular, they are being cut in India and cost around $20/ct.-$25/ct.

Care and cleaning. Feldspars, including orthoclase moonstone, have a hardness of 6-6.5 on the Mohs scale. Although that’s softer than some of the more prestigious gems, it holds up well when worn, as evidenced by the moonstones set in antique and estate jewelry. Moonstones were popular in the Victorian period (1885-1901), and those moonstones seem to have fared well over the years.

Cleaning can be done using anything from the mild soap-and-water technique to the more aggressive ultrasonic solutions. “It’s really no different than cleaning gold,” says Dunay. “Boiling or steaming” is just fine, he says.

Bench repair and setting. Moonstone can be easily bruised at the bench by any metal tool. However, if a stone is accidentally scratched, the damage can be polished out.

Recommended reading. Robert Webster, Gems, fifth edition, 2002, Butterworth-Heinemann; and G.F. Kunz, The Curious Lore of Precious Stones, 1989 reprint, (1913 Lippincott Press).

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