Moonstone: The Floating Light of Adularescence

History

Moonstone, with its mysterious sheen reminiscent of moonlight, has been treasured across civilisations for thousands of years. The ancient Romans believed it was formed from frozen moonlight. It has long been associated with fertility, love, and protection. This gem, a popular choice for jewellery, is especially favoured in Germany and the Scandinavian countries, where it's preferred over pearls and alexandrites as a June birthstone.

Mineral Origins

Moonstone is a variety of the feldspar group mineral orthoclase. Its characteristic shimmer, known as adularescence, is caused by light scattering between microscopic layers of feldspar. During formation, orthoclase and albite separate into alternating layers. The diffraction of light as it hits these thin, alternating layers produces the floating, cloud-like light within the gem. The finest moonstones are found mainly in Sri Lanka and Southern India. Other varieties can be found in locations around the world, such as Australia, Armenia, Mexico, Brazil and the United States.

The 4 C's

When selecting a moonstone, buyers consider the four Cs: colour, clarity, carat, and cut.

Colour

The ideal moonstone exhibits a transparent, colourless body with a pure blue, medium-toned sheen. However, moonstones can occur in many body colours, including peach-pink, brown, yellow, and blue. Any body colour detracts from a moonstone's value, and unattractive green hues will significantly lower the price. The adularescent effect can also occur in many colours. White is popular, though not as valuable as blue. The most valuable moonstones are colourless with a strong blue sheen, and any noticeable body colour, especially green, lowers the price. The sheen should be centred on the top of a cabochon and easily visible from different angles.

Clarity

Moonstones are considered Type II clarity gems, which means they usually contain inclusions visible with magnification. It's best to buy eye-clean gemstones, where inclusions are not visible without magnification. "Caterpillar" or "centipede" inclusions can confirm the stone's identity as a moonstone. These inclusions are short pairs of cracks, running parallel to the vertical axis of the crystal, with shorter cracks emanating perpendicularly. These look like many-legged insects under magnification. Moonstones can also have dark rectangular areas due to stress cracking or cavities, and sometimes a cavity extends from the rectangular area creating a comma-shaped inclusion.

Carat

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 because of their increased rarity. While moonstones are available in a wide range of sizes, fine material is rare in large sizes, which increases its value.

Cut

To best display adularescence, moonstones are most often cut in a high cabochon. Flatter cuts won't exhibit as much sheen. Lapidaries also cut moonstones into beads or facet them for greater brilliance. Faceted moonstones have become more common, as the cut enhances brilliance and hides inclusions. Carved moonstones are popular, but some carvings can hide inclusions or fractures, or reduce adularescence. If a moonstone is cut as a cabochon, its dimensions should be uniform, and the profile should not be too flat.

Be Aware Of

When buying a moonstone, it is important to consider enhancements, simulants, and synthetics.

Enhancements

Although uncommon, a treatment that impregnates moonstones with an organic substance has been found. This procedure improves adularescence and will cause the gem to fluoresce under ultraviolet light.

Simulants

Other materials are often used as moonstone simulants. Some sellers may 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. Opalite, a type of glass, makes a particularly convincing moonstone simulant.

Synthetics

Lab-created moonstones have not yet entered the market.

Final Thoughts

Here are some final considerations when looking to buy moonstone jewellery.

Buying Tips

Most moonstones are inexpensive, however, it is wise to keep a few things in mind when purchasing. Always choose an appropriate jewellery setting, and watch out for undisclosed treatments and simulants. The more transparent and colourless the body, and the more blue the adularescence, the higher the moonstone's value.

Jewellery Care

Moonstones are relatively soft, measuring 6-6.5 on the Mohs scale, making them vulnerable to scratching and chipping. Therefore, protective jewellery settings or use in pendants or earrings are recommended. Avoid wearing moonstone rings during sports or at the gym. To clean moonstones, use only warm, soapy water and a soft brush, and don't use mechanical systems like ultrasonic or steam.

Sources

Cited gemological sources
Authority	Title	URL
GIA	Gemological Institute of America, Moonstone encyclopedia + quality factors	gia.edu/moonstone
IGS	International Gem Society, Moonstone buying guide + Moonstone value, price, and jewelry information	gemsociety.org/article/moonstone-jewelry-and-gemstone-information
AGTA	American Gem Trade Association, Moonstone reference	agta.org/gemstones/moonstone
AGS	American Gem Society, Moonstone (June birthstone) reference	americangemsociety.org/birthstones/june-birthstones

Frequently asked questions

Does moonstone come from the moon?

No. Moonstone is a feldspar formed on Earth, and the name describes the floating blue to white glow, called adularescence, that resembles moonlight. That glow comes from light scattering between microscopic alternating layers of two feldspars inside the stone. There is no connection to the moon beyond the resemblance.

What causes moonstone's floating glow?

The effect is called adularescence. As the stone formed, feldspar separated into alternating microscopic layers, and light scattering between those layers produces the soft, cloud-like sheen that seems to float beneath the surface and move as you tilt the stone. A high cabochon cut shows this glow best.

Does moonstone change colour?

Not in the sense that alexandrite does. What moonstone shows is adularescence, a glow that appears to float and move across the surface as you tilt the stone or move the light. The body colour stays the same. If a stone genuinely shifts hue under different lighting, it is not moonstone.

Is rainbow moonstone real moonstone?

Not in the strict sense. Classic moonstone is orthoclase feldspar, while rainbow moonstone is a trade name for a type of labradorite, a related feldspar that flashes blue and multicolor sheen. It is a genuine, attractive feldspar gem, just not the same mineral. A seller should describe it accurately.

How can I tell real moonstone from glass or opalite?

Genuine moonstone often shows tiny caterpillar or centipede inclusions under magnification, which help confirm it. Glass and opalite imitations instead show swirls and round bubbles, and the sheen looks more uniform and artificial. These clues help, but a gemologist gives the definite answer if you are paying a meaningful price.

Is peach or pink moonstone real moonstone?

Yes, both are genuine feldspar. Peach moonstone is orthoclase with iron giving the warm body colour and usually a softer, whiter sheen. What is sold as pink moonstone is often the same material under a different name. Dyed white moonstone is also passed off as pink, so ask.

Is moonstone treated?

Usually not, which is part of its appeal. An uncommon treatment impregnates the stone with an organic substance to boost the sheen, and that material tends to glow under ultraviolet light. Most moonstone you see is natural and untreated, but a reputable seller should still disclose any enhancement.

What is the most valuable kind of moonstone?

The most prized moonstone has a colorless, transparent body with a strong blue sheen that sits on top of the cabochon and stays visible from different angles. White stones are popular but less valuable, and any noticeable body color, especially green, lowers the price. The finest material comes mainly from Sri Lanka and India.

Why are most moonstones inexpensive?

Moonstone is widely available, so everyday pieces are affordable. Value climbs sharply only for the rarer combination of a clean, colorless body and a strong, well-centered blue sheen in larger sizes. Most stones do not reach that level, which keeps typical moonstone jewelry within easy reach.

Are moonstones rare?

Ordinary moonstone is common and inexpensive. Fine material is not. A colourless, highly transparent body with a strong blue sheen, historically from Sri Lanka, is genuinely scarce and commands many times the price of the cloudy white and rainbow material that fills most retail jewellery.

Is moonstone durable enough for a ring?

Only with care. Moonstone is fairly soft at 6 to 6.5 on the Mohs scale and has cleavage, so it scratches and chips more easily than harder stones. It is ideal for pendants and earrings, or a protected ring setting. Avoid wearing moonstone rings during sport, and skip ultrasonic and steam cleaning.

Can moonstone get wet?

Briefly, yes, but treat it as delicate. Moonstone is 6 to 6.5 on the Mohs scale with perfect cleavage in two directions, so it is more vulnerable than most gems. Remove it before swimming, and never use ultrasonic or steam cleaning. Wipe it with a soft damp cloth instead.

Does moonstone fade in sunlight?

No. Adularescence is a structural optical effect produced by layering inside the stone rather than a pigment, so sunlight cannot fade it. The stone's real enemies are impact and heat, which act on its cleavage. Dyed moonstone imitations can fade, which is one way to spot them.

Which month is moonstone the birthstone for?

June, and it is one of three. GIA lists pearl, alexandrite, and moonstone for June, one of only three months carrying three birthstones. Moonstone is by a wide margin the most affordable of them, which is why it dominates June jewellery at lower price points.