Moonstone

Moonstone is the most well-known gemstone variety of orthoclase feldspar, a potassium aluminum silicate. It is a transparent to opaque oligoclase, a variety of plagioclase albite and sheet mica. Moonstone is known to exhibit a distinct sheen under certain lighting conditions, and it is the sheen which renders moonstone one of the most remarkable gemstones available today. In fact, its name is owed to the almost magical, bluish white shimmer it exhibits, which closely resembles that of the moon. Gemologists refer to the shimmering optical phenomena as ‘adularescence’.

The optical effect of adularescence is a result of moonstone’s unique structural pattern. Tiny inclusions of albite, a sodium aluminum silicate, are intermixed with host rock layers of orthoclase, a potassium aluminum silicate. The alternating layers of different feldspars form a lamellar (scaly) structure which causes the interference of light as it enters the stone. Thin layers of alternating silicates tend to refract more attractive and colorful sheens, whereas thick layers of silicates produce less attractive, white to colorless sheens. As light enters the stone, it is refracted and scattered, producing an extremely unique and attractive play of both color and light. With moonstone, the aura of light actually appears to glow from deep within the surface of the stone.

Moonstone Color

Moonstone is typically colorless, but it can occur in a wide range of colors, including gray, mocha brown, yellow, orange, green, pink, blue and white. It most often exhibits a white to bluish-white sheen, but other sheens can occur such as silvery and blue-orange. Sri Lanka’s moonstones with a pale blue sheen on a near-transparent body are considered most valuable. India’s moonstones show cloudlike plays of light and color which are very valuable including beige brown, green, orange or simple brown. Rarer colors include blue, peach, smoke, champagne, black and red.

Moonstone Clarity and Luster

Moonstone typically occurs with translucent clarity. Transparent specimens are uncommon, but not unheard of. Transparent moonstone is considered most valuable. Moonstone has an attractive vitreous to pearly luster when cut and polished.

Some moonstones can exhibit chatoyancy. In the trade, these are known as ‘cat’s eye moonstone’. Other rare varieties of moonstone can occur with asterism effects. These are referred to as ‘star moonstone’. Cat’s eye and star moonstones are exceptionally rare and highly desirable.

Moostone Cut and Shape

Moonstone is almost always cut en cabochon to maximize the desirable effects of adularescence. With moonstone, the orientation of the cut is very important. Appropriate height of the stone is essential to display the peaked light reflection, which is why most moonstone is cut with a high dome. Cutters must locate the crystal axis exactly in the zenith of the stone in order to achieve perfect orientation which results in maximized schiller effects. Moonstone is often cut in oval shapes since ovals tend to preserve the most carat weight. Some highly transparent stones may be faceted, but faceted moonstone is extremely rare.

Moonstone Jewelry

Though moonstone is not as hard as most other types of jewelry gemstones, it remains one of the most popular gemstones for jewelry. In fact, moonstone jewelry has been worn for centuries, dating back to ancient Greek and Roman civilizations.

Moonstone jewelry should be limited to protective-style jewelry applications, such as earrings, pendants, pins and brooches. Moonstone can also be worn as rings, but care should be taken to prevent scratches and blows. The wearing of moonstone rings should be limited only to occasional wear as moonstone gems are not durable enough to handle everyday wear and tear like quartz or other harder gems. Moonstone is most often faceted, but some transparent materials may be faceted and these faceted stones are excellent for open settings, such as prongs. When cut en cabochon, designs are limited to closed style settings which can accommodate flat backs.

Source: Gem Select