Moonstone Value, Price, and Jewelry Information

Moonstone, Meetiyagoda, Southern Province, Sri Lanka. Photo by Géry Parent. Public Domain.

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Moonstones are feldspar gemstones with varying compositions. Typically, they’re orthoclase feldspars with alternating layers of orthoclase and albite.

Like their evocative namesake, the Moon, moonstones have inspired quite a bit of romantic lore. Jewelry lovers, especially royalty, have highly valued these gems for centuries. Currently, they’re probably most popular in Germany and the Scandinavian nations, where they’re preferred over pearls and alexandrites as June birthstones.

Sterling silver brooch with inset moonstone cabochons, designed by the Danish jeweler Georg Jensen, 1914. Photo courtesy of liveauctioneers.com and Butterscotch Auction.

What Causes Moonstone Adularescence?

Moonstones are sometimes called “adularia” after Mt. Adular in Switzerland, a famous source for these gems. Mt. Adular has also lent its name to moonstone’s characteristic, phenomenal effect.

Moonstone crystal showing adularescence, Mt. Adular, Tessin, Switzerland, 7 x 6.5 cm. Photo by Didier Descouens. Licensed under CC By-SA 3.0.

Adularescence is caused by the diffraction of light as it hits thin, alternating layers of orthoclase and albite within the gem. This produces the appearance of a floating, cloud-like, blue to white light inside the gem. In orthoclase moonstones, a blue sheen is produced if the albite crystals are very fine. (Fine orthoclase and albite plates are dispersed within each other as a result of unmixing on cooling). If the albite plates are thick, the sheen is white.

Moonstone rough and cut set, 4.3 x 4.1 x 3.7 cm (crystal, Tvedestrand, Norway), 2.11 cts, 1.35 cts (gemstones, India). © Rob Lavinsky, www.iRocks.com. Used with permission.

Moonstone Varieties

Generally, lapidaries cab moonstones with high domes to accentuate adularescence. Specimens with strong displays often reveal cat’s eyes when cabbed in this manner. Rare asterism, when it occurs, produces four-legged stars.

Cat’s eye moonstone, 6.01 cts, oval cabochon, Sri Lanka. Photo courtesy of liveauctioneers.com and Jasper52.

The body color of an orthoclase moonstone is generally due to its iron content and may be white, beige, brown, red-brown, orange, greenish, or yellowish. Goethite (iron oxide) inclusions will cause red coloration.

A moonstone variety containing the orthoclase feldspar sanidine occurs in Grant County, New Mexico, United States.

Rainbow Moonstone

Some transparent plagioclase feldspars, such as labradorite, also have thin layers of albite. These also produce a blue schiller effect if thin and a white effect if thick.

In rare instances, a multicolored schiller displays blue with green and/or orange colors, a phenomenon known as labradorescence. Although such stones are often called “rainbow moonstones,” they’re technically a variety of labradorite, not moonstone. Labradorescence is distinct from adularescence. However, the gem trade has generally accepted the use of the name “rainbow moonstone.”

A cushion-cut feldspar gem or “rainbow moonstone” with multicolored labradorescence, 1.37 cts, 8.4 x 5.8 mm, Madagascar. © The Gem Trader. Used with permission.

Identifying Characteristics

Inclusions

Moonstones are one of the few gems that have inclusions so characteristic that seeing them guarantees their identity. They contain fissure systems along incipient cleavages in the body of the material created by exsolution pressures. Such fissure systems are short pairs of cracks, running parallel to the vertical axis of the crystal, with shorter cracks emanating perpendicularly along the length of the parallel fissures. These resemble many-legged insects under the microscope and are known as “centipedes.”

Moonstones also have rectangular dark areas due to stress cracking or cavities. Sometimes, a cavity extends from such a rectangular dark area, creating a comma-shaped inclusion.

Myanmar moonstones characteristically have oriented needle inclusions.

Specific Gravity and Refractive Index

Material from Sri Lanka tends to have specific gravity values on the low end of the moonstone scale, 2.56. Material from India tends toward the high end, 2.59.

Most moonstones usually have refractive indices (RI) of 1.520-1.525, with a birefringence of 0.005. However, material from Virginia has an RI of 1.518-1.524, with a birefringence of 0.006.

Moonstones: India and Sri Lanka (~ 5 each). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Synthetics

Although moonstone has been simulated by milky chalcedony and certain types of synthetic spinel, these substitutes usually look inferior and are easily spotted. Lab-created moonstones haven’t entered the market.

Moonstone gems, left to right: cabbed, carved, and faceted. Photos courtesy of Barbara Smigel, Artistic Colored Stones.

Sources

Historically, Myanmar has produced the finest material.

Other notable sources include the following locations:

• Australia; Austria; Finland; India; Madagascar; Mexico; Norway; Sri Lanka; Switzerland; Tanzania.
• United States: New Mexico; Virginia.

Moonstone mine, Meetiyagoda, Sri Lanka. Photo by Wouter Hagens. Public Domain.

Sizes

Moonstone is rare in both large size and fine quality, but Indian material with strong body color is abundant and very inexpensive. This is fortunate, because the material is usually well-cut and very attractive. Moonstone with a blue sheen, the most valuable kind, rarely occurs in sizes over 15-20 carats. However, stones with a silvery or white adularescence are abundant and available in sizes up to hundreds of carats.

Discovered by the first Japanese expedition to Mt. Kilimanjaro in 1918 and reputed to weigh between 300 and 450 carats, this might be the largest known moonstone. Photo by Mr Matthew Hardy Japan. Licensed under CC By-SA 3.0.

Care

Although popular jewelry stones, moonstones have a hardness of 6 and a slight tendency to chip and cleave. They should receive protective settings, especially for ring use, to prevent scratching. Brooches and pendants will minimize exposure to hazards, but, in any jewelry setting, protect moonstones from hard knocks. Don’t use mechanical systems like ultrasonic or steam for cleaning. Instead, use only warm, soapy water and a soft brush.

Consult our gemstone jewelry cleaning guide for more information.

Moonstone jewelry. Photo by Christiane Birr. Licensed under CC By-SA 2.0.