The Furor Over Feldspar

Until recently, brick - and salmon-red sunstone - both clear and with schiller - were rarities. True, renewed mining of this feldspar in Oregon - generally conceded to be the source of the world's best sunstone - brought more fine colors on the market than had been seen in years. But fine stones cost at least $100 per carat, usually far more.

Then, in early 2007, look-alikes costing $40 per carat suddenly hit the market in impressive numbers. None of its sellers called it sunstone. Instead, most called it andesine, which is a first cousin of labradorite (the scientific name for sunstone) in the plagioclase series of feldspars. [Plagioclase consists of six species, identified according to the ratio of calcium to sodium - their two predominant chemical components.] This next-of-kin gemological status invited many consumers to think of andesine as an affordable alternative to pricier Oregon sunstone, especially because sellers swore it was all-natural.

Then one of the leading on-air and on-line marketers of andesine - Knoxville-based Jewelry Television - did an about-face and admitted stones were treated to attain their beautiful colors. Buyers were offered full refunds for their andesine purchases.

The question remained: How were the stones improved? A buyer at JTV told Colored Stone that the network believes stones were treated using a repeat process involving two exposures of stones to 30 days of heating followed each time by tumbling. That would seem to indicate diffusion of copper - sunstone's chief coloring agent - was involved. It would also seem to indicate that Mexico, which produces tons of straw-yellow low- or no-copper labradorite, may be the source of the so-called andesine.

But no matter where the treated andesine is produced, why perform the process twice? One American treater theorizes that the interaction of feldspar with copper may create a diffusion-resistant color coating, similar to the cobalt coating created when using diffusion to color topaz. This diffusion shield may require tumbling to remove it, followed by further heating for deeper color penetration.

At this point, all is conjecture. Presently, GIA and Cal Tech are conducting research on these suspect feldspars to determine the exact cause of their color. But an answer isn't expected for months. What does one do in the mean time? We recommend sticking with Oregon sunstone - that is, if you want all-natural, all-American feldspar.

A Sunstone Mining Renaissance

This isn't the first time that Oregon sunstone has caused feldspar fever. Discovered in 1980 in eastern Oregon, the gem gained instant acclaim for its never-before-seen brick reds and spruce greens. Another plus in its overnight popularity: transparency. Until then, most sunstone that jewelers saw was translucent material from India, suited for bead and cabochon cutting. Oregon quickly overtook India in all existing quality categories and topped it with unprecedented amounts of facetable material.

By 1991, sunstone was the fourth most important U.S. gem in terms of dollar value - leaping ahead of tourmaline. That year, the Bureau of Mines reported Oregon's feldspar output was worth $1.5 million - three times the preceding year's total. Of this amount, at least four-fifths came from the Ponderosa Mine - then and now the state's biggest sunstone mining operation.

In 2003, financiers John and Talley Woodmark, as well as Bruce Moore took over operation of the mine, renamed it Desert Sun Mining and Gems, and gradually pushed annual production from its previous mid-1990s peak of 400 kilos to 860 kilos last year. "The secret," says John Woodmark, "is mechanization. We knew that if ever we were to make a fully functioning market in Oregon sunstone we had to have large, easily replenished stockpiles of every size and shape we offer."

With 500,000 carats of Ponderosa's desirable orange, red, pink and green stones on hand (plus another 250,000 carats of pleasingly mild yellow material), Woodmark believes he can inspire confidence in sunstone among major chains. And don't forget the Dust Devil, Spectrum and Outback sunstone mines over in Plush, which are estimated to account for another 250,000 carats of colored sunstone.

Oregon sunstone mines have wisely pursed a two-pronged approached to popularization. First, they recruited leading lapidaries like Dalan Hargrave, Glenn Lehrer, John Dyer and Larry Woods to craft their top-grade roughs into prize-winning, publicity-grabbing gems and carvings. Second, they've been mindful of the need to keep their sunstone prices low. So they have farm out the lion's share of calibrated and free-size cutting to Chinese and Indian factories. Desert Sun prides itself on always having 400 of every calibrated size and shape they offer in stock. "Commitment to customer needs is essential for success," Woodmark says.

That's one way to keep sunstone affordable. Face it, price is a compelling factor in sunstone's new appeal. With the cost of popular pinkish red spinels and orangey garnets on a steep, steady ascent, similar-color sunstone offers substantial price relief - without any sacrifice of beauty and only slightly less hardness (sunstone is 6.5 to 7.2 on the Mohs scale compared to 8 for spinel and 7 to 7.5 for tourmaline).

What's more, Oregon, which is blessed with more transparent stones than any other sunstone locality, is a looks leader - boasting deep mandarin orange and imperial topaz reds; salmon and October-leaf pink; purplish reds; and spruce greens. No other sunstone locality has been known to produce as many colors. In fact, the Western Hemisphere's largest rival region for sunstone in northern Mexico is known principally for straw-yellow stones.

Oregon sunstones are commonly bi-colored and frequently feature stunning greens framed in, or intersected by, red. The unexpectedly prolific sight of these two-toned stones at this year's Tucson Gem Show, says Helen Driggs, managing editor of Jewelry Artist, "detoured me from my search for watermelon tourmaline to sunstone."

Multi-hues weren't the gem's only virtue that made her eye it and buy it. Oregon sunstones are famous for copper platelet inclusions which, when densely populated, reflect light in shimmering sheets that impart a phenomenon called "schiller" to stones. Driggs calls this "sunstone's unique rosy glow" and likens it to "the gemological equivalent of orangey northern lights." No wonder schiller-rich salmon-red Oregon sunstone briolettes are the biggest seller at Portland-based Rogue Gems which specializes in Oregon sunstone.

Disorder Below the Border

It would be nice to report that most Oregon sunstone is red, orange or green. But such colors account for 15 percent of mine output. Another ten percent has attractive schiller and the remainder is what miners call "clear," a word that refers to mostly soft-yellow and off-white hues. And we haven't even touched on the enormous amount of material suitable for bead and cabochon cutting.

No matter what the color, Oregon sunstones are all-natural and untreated. This isn't to say that treaters might not be experimenting with ways to produce more desirable colors. But no one we talked to versed in heat treatment and chemical color diffusion - the methods most likely to be used to turn yellow feldspar red and orange - was aware of the successful application of these technologies to Oregon sunstone.

We raised the issue with treaters because, as said before, Jewelry Television, perhaps the world's largest home-shopping gemstone seller, recently did on-air and on-line mea culpas, complete with refund offers, for selling treated Asian andesine as all-natural. Why the turn-about?

No one really knows where any of the suspect andesine is coming from. Sellers say it's from Tibet, the Congo, Tanzania - all of the sources mentioned in most standard gemology textbooks. But if you read the descriptions given for this andesine and labradorite in the reference works, they all describe them as possessing colors similar to Oregon's.

Only one cutter that we know of, John Dyer, based in Edina, Minnesota, has actually worked with Tibetan rough, provided by a Chinese supplier he met at the Tucson Gem Show. Dyer says the material does not have the richness of color and appearance he associates with Oregon sunstone and he will not use it again - despite its lower price.

"Do you think it was treated?" I ask him. Dyer says he has no reason to suspect that it is since the supplier assured him it came direct from the mine.

No one else whom we talked to that regularly cuts or sells sunstone has been able to secure or examine any andesine rough. But given recent scandals involving treated ruby and emerald rough, the scarcity of andesine rough only fuels fears of gemological hanky panky. Here's the worst of our fears:

Sunstone owes both its reds and greens to copper, depending on this trace element's valence. If a plagioclase is deficient in this element, then it must be added using, most likely, diffusion. Since Oregon sunstone is strongly endowed with copper, it would seem foolish to risk its sterling reputation adding artificial color by means of copper diffusion. This would only make sense on copper-free material such as that from Mexico, which is producing tons of straw-yellow, low- or no-copper labradorite and selling it to Asian dealers. If Mexican feldspar is the culprit, then you can bet the ranch that this south-of-the-border labradorite owes its color to oven alchemy.

So if you want full-integrity feldspar, stick with Oregon sunstone. Although we have seen top-grade large red pieces selling for over $500, even $1,000, per carat, there is ample fine material available for between $100 and $200 per carat. And there is much medium to better grade goods available for considerably less than $100 per carat. While that's higher than misrepresented felon feldspars from Mexico, we think that's a fair price to pay for tamper-free labradorite.

By David Federman

© Colored Stone – 2008 March

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