By
Ashley Bailey, Monday, August 07, 2006 12:00 AM
Moonstone, a feldspar with uncanny light shimmerings, is the birthstone for June - an honor it shares with pearls. If asked to choose between the two, the vast majority of people select pearls.
Maybe they should hesitate long enough to look at a moonstone before doing so. If the gem they are shown is of fine quality, they will see something truly lovely and unique: a deep blue stone, reminiscent of superb sapphire, with a milky blue sheen.
This sheen is the result of a phenomenon called "chatoyancy," which results from the interplay of light with numerous tiny albite crystals inside the stone. The effect is utterly breathtaking. Indeed, when moonstone was discovered several centuries ago on Switzerland’s Mount Adular (now known as St. Gotthard), the shimmering of these stones was named "adularescence" as a tribute to their origin.
Alas, the blue-sheen moonstones that inspired such nomenclature are hard to come by at present. Sri Lanka, the best modern-day source for such gems, is producing few if any of these stones. India, the next best producer, is producing whiter stones that compensate for their lack of blue with glorious displays of rainbow color - hence their name, rainbow moonstone.
If you are lucky enough to find top-grade moonstone, be warned that with a hardness of 6-6 1/2 on the Mohs scale, and occasional strong cleavage, rings containing them should be worn with care.
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