Moonstones belong to a large mineral group known as the Feldspars and this group makes up more than half of the Earth’s crust. Orthoclase is a variety of the feldspar group and moonstone is its predominant member.
The term adularescence is used to describe the milky ethereal blue light that emanates from moonstones. Also known as the Schiller effect, the unusual sheen is related to the laminar micro crystallization of orthoclase and albite minerals in thin layers. As the light is reflected and refracted, it becomes scattered and diffused to create the unusual optical anomaly.
Traditionally, the classic moonstones with their high transparency and bluish sheen came from Sri Lanka but exceptional stones have always been found in both Burma and India. The best stones are nearly transparent but shimmer with a pale blue light that appears to come from within. In settings or in images, moonstones look best on dark backgrounds which tend to accentuate the blue. Moonstones from India are the most colorful and are available in a broad range of colors including white, beige, brown, green, orange, yellow and blue. In rare instances moonstones may also be multicolored showing blue, with green and/or orange. Such stones are known as rainbow moonstones and are quite valuable in their own right.
In the rough, moonstones are unremarkable with little indication of the mysterious shimmer that lies below their surface. The adularescence is not revealed until the stones are cut and polished. Moonstones are usually cut as cabochons, but some stones are carved and occasionally faceted. Some stones may also show a cat's eye effect or a four-rayed star and some stones are fashioned as beads or cameos and engraved with the faces of children or some version of the man on the moon.
By far the most valuable moonstones are the rainbow stones or those that are colorless and transparent but still possess a strongly blueish sheen. Since bluish moonstones of good color and transparency have become more and more of a rarity, their prices have risen sharply in recent years. In general, the more transparent and the more blue the adularescence, the higher the value. Most of today’s moonstone production is centered around the Bihar state in East India.
When purchasing moonstones the variations in price may be perplexing and range from a few pennies for opaque white stones to hundreds of dollars for large clean blue, green, or rainbow specimens. Stones with a colorless or white adularescence are abundant and inexpensive. The colorful yellow, brown, orange, and creamy Indian moonstones are also popular for their lively and attractive colors as well as affordable price points far below the price of the blue stones. Blue Moonstones are almost never clean and even stones over 2 cts. in weight begin to command prices over $100 per stone. The more intense the color, and the larger and more transparent the stone, the higher the price.
Moonstones are treasures of nature with a sensual and seductive aura. Named after their scintillations mirroring the crescent and waning phases of moonlight, this alluring gemstone is not only looked upon and admired by all, but also so distinctive that it can easily be identified upon sight.