Moonstone is one of gemstone members from orthoclase feldspar which composed of two feldspar species, orthoclase and albite. At first, the two species are intermingled. Then, as the newly formed mineral cools, the intergrowth of orthoclase and albite separates into stacked, alternating layers. So when light falling 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.
Adularescence received its name from “adularia,” an old name for moonstone. The name adularia itself comes from a city in Switzerland, Mt. Adular (now St. Gotthard) that was one of the first sources of fine-quality moonstone.
HOW DO I JUDE MOONSTONE QUALITY?
When buyers select moonstones, they look for three key factors: bodycolor, sheen color, and orientation of sheen.
The most highly favored moonstones should display a colorless, semi-transparent to nearly transparent appearance, without inclusions and displaying a vivid blue adularescence, known in the trade as blue sheen.
Today, the market demand for moonstone is strong.
In 1997, miners in Southern India discovered a new type of moonstone with a bright green bodycolor, described as “parrot green” by the trade and it was wholesaling for between $1 and $8 per carat. This makes it a less-expensive alternative to other moonstone types that have a more traditional look.
Wholesale prices for small, calibrated moonstones are modest.
Larger sizes, above 9×7 mm, tend to be free-form, and they’re priced per carat. In 2012, moonstones weighing from 3 to 5 cts sold for $1 to $10 in commercial quality and $40 to $65 in extra fine quality. There’s a major jump in the price of ovals above 9×7 mm.
In the early 1900s, the gem was popular in both Europe and the United States.
Moonstone is a relatively soft gem, falling between 6 and 6.5 on the Mohs scale. That makes it a good stone for carving into decorative jewelry elements, such as cameos or the popular “man-in-the-moon” face that plays on the gem’s name.
The uneven surface of the carvings combines with the shifting adularescent sheen to create a delightfully intricate and lively effect. In addition to its softness, moonstone cleaves easily.
A good moonstone should be almost transparent, and as free of inclusions as possible. Centipedes can interfere with adularescence. If a moonstone is cut as a cabochon, the dimensions should be uniform and the profile shouldn’t be too flat as very flat cabs don’t display sheen well and have little value.
By far the most common cutting style in moonstone is the cabochon since its phenomena adularescence tend to show up best on rounded surface. Faceted moonstones have become increasingly common. The trend heightens brilliance and tends to hide inclusions, such as the characteristic tiny tension cracks called “centipedes,” named after the many-legged creatures they resemble.In addition to cabs and faceted, moonstone is also shaped into beads for strands, but Moonstone cabochons are usually oval, but recently cutters have offered cabochons in interesting shapes, such as the tapered sugarloaf.