Moonstone

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 jewelry, 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: color, clarity, carat, and cut.

Color

The ideal moonstone exhibits a transparent, colorless body with a pure blue, medium-toned sheen. However, moonstones can occur in many body colors, 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 colorless with a strong blue sheen. 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 jewelry.

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 colorless the body, and the more blue the adularescence, the higher the moonstone's value.

Jewelry Care

Moonstones are relatively soft, measuring 6-6.5 on the Mohs scale, making them vulnerable to scratching and chipping. Therefore, protective jewelry 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.