A ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water.
Moonstone’s delicate beauty and its long-established heritage make it perhaps the most familiar gem-quality member of the feldspar group.
Feldspars are the most widespread minerals in the earth’s crust, as well as some of the most diverse. You can pick up a rock anywhere in the world, and you’ll probably find that it contains a mineral or two from the feldspar group.
Moonstone is a variety of the feldspar-group mineral orthoclase. It’s composed of two feldspar minerals, orthoclase and albite. At first, the two minerals are intermingled. Then, as the newly formed mineral cools, the intergrown orthoclase and albite separate into stacked, alternating layers.
When light falls between these thin, flat layers, it scatters in many directions, producing the phenomenon called adularescence. Adularescence is the light that appears to billow across a gemstone, giving its surface a glowing appearance.
- Mineral: Feldspar
- Chemistry: KAlSi3O8
- Color: Colorless to White, Gray, Green, Peach, Brown
- Refractive index: 1.518 to 1.526
- Birefringence: 0.05 to 0.008
- Specific gravity: 2.58
- Mohs Hardness: 6.0 to 6.5
Birthstones and Anniversaries
Moonstone is a birthstone for June, along with pearl and alexandrite.
Moonstone Gemstone as rough
Perhaps the most captivating aspect of adularescence is its appearance of motion. The misty light seems to roll across the gem’s surface as you change the viewing angle.
Other feldspar minerals can also show adularescence. One is a labradorite feldspar found mainly in Labrador, Canada. Another labradorite—found in Madagascar—has a multicolored adularescence over a light bodycolor. It’s known in the trade as rainbow moonstone, despite the fact that it’s actually a variety of labradorite rather than orthoclase.
Sanidine is another feldspar mineral that can include adularescent gems called moonstones. To be called moonstone, a mineral’s actual identity is not as important as the beauty of its adularescence.
Moonstone History and Lore
According to Hindu mythology, moonstone is made of solidified moonbeams. Many other cultures also associate this gem with moonlight, and it’s easy to see why. Its internal structure scatters the light that strikes it, creating a phenomenon known as adularescence. The visual effect is reminiscent of the full moon shining through a veil of thin, high clouds.
Legends say that moonstone brings good luck. Many believed that you could see the future if you held a moonstone in your mouth during a full moon.
Adularescent moonstone was once called “adularia.” The name originated with a city in Switzerland, Mt. Adular (now St. Gotthard), that was one of the first sources of fine-quality moonstone.
Great designers of the romantic Art Nouveau era, such as René Lalique and Louis Comfort Tiffany, featured the pale gem in custom jewelry. Moonstone was also a favorite among artisans of the Arts and Crafts era in the last half of the nineteenth century, who used it in handcrafted silver items.
During the 1960s “flower child” movement, moonstone provided its wearers with the desired ethereal look, and designers of the 1990s New Age movement again turned to moonstone’s natural beauty for inspiration.
Facts about Moonstone Gemstone
Rare in top qualities, this ethereal gem derives from one of the earth’s most common minerals.
Stacked layers of orthoclase and albite diffract light, creating moonstone’s adularescence.
Besides adularescence, moonstone sometimes also shows a cat’s-eye effect.
The finest moonstone is a gem of glassy purity with a mobile, electric blue shimmer.
Characteristic inclusions include tiny tension cracks called centipedes.
As it displays moonstone’s phenomena to best advantage, cabochon is the common cut.
Moonstone comes in a wide range of sizes and carat weights.