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Rainbow Moonstone

The world of phenomenon gems was dealt a severe blow when Sri Lanka’s deposit of “blue-sheen” moonstone ran dry around 1988. Suddenly, jewelers were without the feldspar—moonstone’s family name—that best displays the special color-play effect called “adularescence” for which this gem family is most known.

Fortunately, the blow was softened by the discovery of a fellow feldspar in southern India. The trade has dubbed the new material “rainbow moonstone.”
Right church, wrong pew.

According to Swiss geologist/gemologist Dr. Henry Hanni, the first scientist to have done extensive chemical analysis of the species, the Indian gemstone belongs to the labradorite branch of the feldspar family while moonstone belongs to the orthoclase branch. The reason: traces of albite and anorthite. For this reason, the stone should properly be called “rainbow labradorite” rather than “rainbow moonstone.”

But it won’t be. The name “moonstone” sounds better. And, besides, the two gems are kissing cousins.

In any case, India’s new labrodorite is rapidly catching on as a replacement for blue-sheen moonstone, or, failing that, a consolation for its loss. And no wonder. The former shows the same kind of spectacular color reflections as the latter—only in multi-colors. That’s good news for lovers of “adularescence” (an optical effect unique to feldspar caused by light interference from its tightly layered crystal structure). Just remember to call it “labradorescence,” please, the counterpart to “adularescence” on the labradorite side of the feldspar family.

As for those who can’t imagine being consoled for the absence of midnight-blue moonstone by a kaleidoscopic-colored labradorite, consider this a possible solace: Rainbow labradorite sometimes boasts a predominant electric-blue color.

There’s only one wrinkle in all this good news from the feldspar front. Rainbow labradorite is fast becoming as hard to find in top grades as the blue-sheen moonstone it replaced. Given the circumstances under which it is mined, it is surprising there is even the little there is.

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Rainbow Moonstone