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Consumers who plan to purchase fine blue moonstones might have to delay their plans indefinitely now that the world’s main vein for this gem in Sri Lanka has run bone dry. What remains in the way of this orthoclase member of the many-branched feldspar family are mostly run-of-the-mill stones that resemble water with milk of magnesia stirred in. The ideal for the species, long treasured in Europe, is “blue-sheen” moonstones. At their best, they are invariably crystal clear with a floating blue to blue-white adularescence on their surface.

A decade ago, when larger blue-sheen moonstones were very plentiful, consumers could buy them for prices comparable to those of the most affordable gems. Nowadays prices for such stones can easily be five to ten times what they were back then. But what can collectors do? The sole source for blue sheens, Meetiyagoda in Sri Lanka, ceased production in 1987. “All most dealers have left are tiny little stones, nothing of any consequence,” says a buyer for a New York cabochon and bead stone importing company. “So it looks like those who want the blue-sheen material in decent sizes are going to have to depend on antique and estate pieces from now on.”

Instead of Pearls

The bleak news about blue-sheen moonstone puts jewelers who sell this gem in a bit of a quandary. A birthstone for June, moonstone is usually considered an alternate to pearl in America. In Europe, it is often the other way around: pearl is a substitute for moonstone.

One of the earliest and best sources of moonstone was St. Gotthard in Swizerland, formerly known as Mount Adular, from which is derived the root of moonstone’s old name, adularia. Although that name is rarely used today, gemologists around the world refer to moonstone’s sheen as “adularescence,’ which means that it results from the interplay of light with layers of tiny albite crystals in these stones. The thinner the layer, the bluer the sheen; the thicker, the whiter.

When choosing moonstones, connoisseurs look for two things: ideal body and sheen color. What’s the ideal? For body color, it’s completely colorless transparency; for sheen, it’s a deep, haunting sky blue which glides across the dome or table of a stone as it is moved against the light.

Like most ideals, the one for moonstone is rarely attained. A moonstone expert estimates that, at most, one out of every 100 Sri Lankan moonstones ever qualified as “blue.” Years ago, when Burma was a big producer of blue-sheen goods, there was no need to stretch this term so far out of bounds. But Burma, like Sri Lanka, can no longer be counted on for any more than an intermittent handful of blue beauties. Although America, Mexico and Tanzania, among others, produce moonstone also, output is sparse and far from the ideal.

This leaves collectors who wish to buy with moonstone little choice but to make do with lesser grades. Don’t get us wrong. Some of the skim-milk blues to sage-beard whites are very lovely. Moreover, with their soft, lustrous appearance, it is easy to understand why birthstone list compilers assigned moonstone an understudy role for pearl. Its low cost is certainly a consoling factor. What’s more, prices drop very sharply for stones whose body color becomes increasingly brownish or which show the tiny stress marks that are a characteristic of this stone. Or one can desert blue sheen entirely in favor of special effect moonstones and even other feldspars altogether.

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