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Andesine Feldspar

Written by Modern Jeweler On May 2, 2013.

Editor’s note: Andesine feldspar is currently the subject of several lawsuits. For more updated information on this gem, check our Gem Profile on Oregon sunstone. The following is the original text from our March 2006 Gem Profile, which was written when the attractive and mysterious material was first appearing on the market.)

ANDESINE: Red-Hot Feldspar

You’ve got to hand it to Jewelry Television, the 24/7 gemstone shopping network based in Knoxville, Tennessee, that has positioned itself as a gemological Discovery Channel. The station knows good things when it sees them. And when, as is often the case, it’s the first to lay eyes on an affordable new gem, it lays enough cash on the table to make sure no one else will see it until it has built a thriving market. With a viewer base of 65 million people, the network often needs months to satisfy large audience appetites.

Nevertheless, Jewelry Television doesn’t blindly lunge into new stones. Because it takes so many risks, it must temper need with caution, giving each newcomer several screen tests to see if it will merit voracious stocking. Of all the gems the network has premiered, none has risen to quicker popularity than andesine, a red plagioclase feldspar whose origins remain a closely guarded-or deliberately muddled-secret. At first rumored but never confirmed to be from the Congo, the current source is most likely western China, possibly neighboring Mongolia or Tibet.

From a marketing standpoint, andesine has all the traits of a Chinese-origin or Chinese-controlled gem. That usually translates into a sell-now, sell-all-you-can philosophy. Since Tucson 2004, supplies of red (as well as green) feldspar have been near ceaseless, something which has worked to Jewelry Television’s advantage ever since it first took a chance on the gem when introduced to it at the show.

Chinese dealers priced their andesine to move from the start. But once this feldspar proved a winner, Jewelry Television bought it in price-pummeling bulk. Last month at Tucson 2006, the network purchased tens of thousands of carats just from two suppliers-and put in open-ended orders for future production when and if it materializes. “Demand is staying way ahead of supply on this one,” says buyer Jay Boyle.

No wonder the station charges $80 to $200 per carat-depending on color, clarity, and size-for the four hues of andesine it offers: red, orange-red, orange, and honey-red. While some exceptional stones fetch more, even their several hundred dollar-per-carat prices reflect the network’s immense checkbook leverage. What makes andesine so telegenic? At its best, this gem boasts a rich red that invites show hosts to compare it to ruby. Is this an exaggeration? “With a below-average return rate for andesine, shoppers are obviously happy with what they receive,” says gem buyer Shawn O”Sullivan.

Incredibly, more than 90 percent of the andesine Jewelry Television sells is loose, which suggests that most buyers are collectors-or, perhaps, still pondering ultimate use. Since network customers tend to be versed in the gems they buy, they probably know andesine has a hardness of 6 to 6-1/2, which should deter mounting in rings. But so does tanzanite and that’s been finger fare for nearly two decades.

As andesine’s red glare spreads off screen to jewelry stores, the gem is coming under intensive gemological scrutiny. Like garnet, feldspar is a large, sprawling family and classification has been tricky, if not controversial. So before putting the stone on air, Jewelry Television asked GIA for nomenclature guidance which it is now following-until or unless the institute changes its thinking.

IDENTITY PROBLEMS

Before andesine appeared, the best red feldspar available was medium-toned, orangey material from Oregon known as sunstone because of its shimmering reflections called aventurescence (schiller) from tiny crystals clustered inside. Sunstone, which is a market rather than a mineralogical name, belongs to the oligoclase branch of the feldspar family-a family that needs genealogy charts to figure out precise memberships in it.

Apparently, andesine is an intermediate member between oligoclase and labradorite, just on the borderline with the latter. Such overlapping chemistry tempts merger names such as “andorite” and “labrasine.”

Overall, family placement in the six member (albite, oligoclase, andesine, labradorite, bytownite, and anorthite) plagioclase group depends on several factors, including refractive index (around 1.55) and shifting ratios of albite to anorthite (the flanking members of this group).

One thing for sure, andesine is not sunstone because it lacks schiller and is usually far deeper in color. However, we’re not too excited about calling it red labradorite either. To us, that’s like calling pink or even golden sapphire by the name of ruby, especially since only a small percentage of andesine is real red in the sense that sapphire is true blue. What’s more, andesine also occurs in green that exhibits other colors such as red in alexandrite-fashion under different lighting conditions.

Here we come to one of the most curious elements in the andesine success story. Red andesine is the first feldspar I can think of that is appreciated for pure monochromatic color the way, say, spinel is.

It is green andesine that is more characteristic of feldspar because it lives up to traditional expectations of color play and other special effects for this gem group. Remember that moonstone and rainbow labradorite are among the most famous feldspars-and both are celebrated primarily for their blend of color and appearance. On the other hand, red andesine finally puts feldspar in a color class with red corundum to which its very likable best stones are justly likened.

Andalusite

Written by Modern Jeweler On May 2, 2013.

Some gems seen to be victims of that oft-repeated childhood proverb: If you can’t say anything nice, don’t say anything at all. Andalusite, found principally in Brazil but named after Andalusia in Spain, its earliest source, is one of them.

For sure, this gem has its devotees. But most of them keep their devotion low-key and Platonic. With friends like that, it is hardly surprising that andalusite stays a victim of the silent treatment. Even those landmark studies of gemology, Max Bauer’s “Precious Stones” and Robert Webster’s “Gems,” pay scant attention to this member of the silicate family.

Certainly, one can easily make a case against andalusite. For starters, stones are often afflicted by annoying amounts of gray and brown. Next, fine qualities are hard to find in sizes over 5 carats. No matter what the size, rutile needles are often visibly present, detracting further from this stone. Last, distinct cleavage (susceptibility to breaking along certain crystal planes) can pose a problem when setting this gem in jewelry.

Yet one can just as easily make a case for andalusite. At its best, it offers unique, lovely color for very little money. “You don’t look to andalusite to find perfection in any one color,” says a Virginia collector and gem specialist. “You look to it to find vivid color contrast.”

That’s because andalusite is a pleochroic stone, meaning it gives off different colors when viewed in different directions. With most pleochroic stones, cutters try to minimize this effect, concentrating on obtaining one predominant color. For example, when cutting tanzanite, they will shoot for an optimal Kashmir blue, extinguishing as much as possible the stone’s strong violet component.

Cutters change the rules when it comes to andalusite. Here they shoot to maximize pleochroism. The stone’s two basic hues, yellowish green and orangy brown, aren’t very often pleasing enough in themselves to emphasize one over the other. But when cut to be played off against each other, stones take on new life through sharp color contrast. The intensity of this contrast is what beauty in andalusite is all about. Yet this unique aesthetic makes andalusite an acquired taste.

The “Phenomenon” Fallacy

Education is the key to connoisseurship of andalusite. But it is hard to educate consumers about andalusite since its best colors are difficult to describe. Try to imagine, if you will, a cushion or emerald-cut stone with a pronounced middle area of a light, sometimes steely, yellow green that gives way abruptly on each side to sharply contrasting end areas of bronze or purplish orange-brown. This is how the dramatic color-play in this gem appeared in the finest specimens we were able to see.

While some dealers told us to look for pink in the brown, we observed it only in all-brown round stones and never in fancy shapes (where strong pleochroic effects are best emphasized)- at least not the ones shown to us. Occasionally, all-pink or all-green stones are cut, but the few we saw were rounds with very hazy, cloudy colors, of interest only to collectors.

However, we mention these pinkish-brown and grayish-green stones because it is their colors that most reminded us of those found in alexandrite, a color-change gem to which andalusite is so often compared that it is called “the poor man’s alexandrite.” If meant as a compliment, it is a backhanded one that virtually dooms andalusite’s appeal, although it is clear that the gem may once have been sold as the far more costly chrysoberyl. Bauer hints as much in the 1909 edition of this book, “Precious stones.” Why the confusion?

Alexandrite is a chrysoberyl that changes color like a stoplight when viewed in different lighting conditions. In daylight, stones exhibit strong greens variously modified by yellow, brown and gray. At its best, this green can resemble that of a bluish -green tourmaline; at its worst, a light olive brown-green. Under artificial light, alexandrites display red, often modified by purple and brown. At its best, this red is raspberry-like; at its worst, a muddy purplish-brown. Because it changes body color in different lighting environments, alexandrite is classified as a “phenomenon” stone.

Andalusite, on the other hand, is not a “phenomenon” stone. It does not change color the way alexandrite does. It simply displays different colors at the same time, thanks, as we said, to its strong pleochroism and, of course, proper cutting. What’s more, these colors bear some resemblance (but not a strong one) to those of alexandrite. For instance, the purplish orangy-brown of fine andalusite is a far cry from the raspberry red of fine alexandrite.

A Narrow Niche

As of now, andalusite jewelry is a rarity. The few jewelers who know about it tend to be colored stone specialists with training in gemology who stock it more out of curiosity than enthusiasm. As a result, consumers are far more likely to see it loose than mounted and in a very small selection, possibly just one stone. That’s hardly enough to inspire interest in the gem.

Yet, as our photograph of andalusite shows, the gem has a striking beauty that lends itself to jewelry usage. With a hardness of 7-7 1/2 on the Mohs scale, andalusite also boasts durability. Because andalusite is so seldom featured in jewelry, its cost will be quite reasonable, at least in sizes under 5 carats. And below 3 carats, where fine andalusite is the most abundant, it’s downright inexpensive.

Therefore, low price, coupled with distinctive beauty, makes andalusite a perfect candidate for standout jewelry pieces. As one jewelry designer familiar with the gem put it: “The high color contrast makes it sure to get noticed. And isn’t attracting attention what wearing jewelry is all about?”

Ammonite

Written by Modern Jeweler On May 2, 2013.

Mother Nature is an artist who loves to leave her marks on minerals. Sometimes, as in the case of agates and jaspers, she is a naturalist, painting landscapes of every description. Other times she is a symbolist, etching primal patterns on the surfaces of things. One of her favorite materials for symbolic designs during the past 400 million years was the ammonite, a predecessor of the modern-day chambered nautilus. Both are cephalopods, a marine phylum that includes the squid and octopus.

In recent years, ammonites have become probably the most popular fossil gem with silversmiths, jewelry artisans, and other crafts people. Writer and graphic designer Michael Green, author of The Illustrated Rumi, thinks he knows why. “The spiral shape with its expanding, logarithmic progressions, is a reminder that there is a cosmic order to things and a call to find it in our chaotic time,” he says.

Green opens his book. There he shows an enormous wave like those seen in Japanese paintings coming forth from a great emptiness (known in Buddhism as “the Void”). Each symmetrical curl of the wave looks like it has been copied from the shell of an ammonite. “Many like me believe there is an essence that precedes existence,” he continues, “and one of its symbols is the great expanding spiral. Ammonites have these spirals hand-painted, as it were, by nature herself.”

There are names for such profound, universal symbols. One of the oldest is “archetype” and one of the newest, a word Green uses frequently, is “fractal.” A fractal is a complex geometric pattern exhibiting basic repetitive elements that are the same no matter what the scale of the structure. The parts of a fractal do not have to be identical in shape or size; there just has to be enough similarity between them to classify them as the same basic type. An ammonite is fractal because it repeats the same basic chamber pattern in progressively larger sizes, always unfolding in a spiral shape. For this reason, Green calls the ammonite “a fractal gem.”

Silversmith and fossil gem devotee Amy Kahn Russell, Ridgefield, Connecticut, agrees with Green about the deep mystical appeal of the ammonite. Before she became a jewelry maker, she was a sculptor. “The very first work I did was a chambered nautilus,” she recalls. “That shape just came to me out of the depths of my imagination.”

Jeweler John Bajoras, owner of the four-store Village Silversmith chain in Rockport and Gloucester, Massachusetts, calls “ammonites the ultimate ‘New Age’ gem, proclaiming a basic unity in creation. People get goose bumps seeing that such patterns regularly occur in nature.” No wonder he keeps dozens of them in each store.

A funny thing about fractals: They have as much to do with chaos as order-and suggest much greater kinship between the two than most people suppose. That’s why computer modelers love them. One fractal named the Phoenix set (it can be viewed at the Wikipedia article on fractals) at first seems to look like an irregular-shaped island. But as it is enlarged, it appears to consist of very regular-shaped logarithmic chambered spiral patterns eerily similar to those on the ammonite shell.

THE SCIENCE BEHIND THE BEAUTY

The ammonite’s pattern serves as a kind of living blueprint to its shell-housing architecture. Imagine a deserted curvilinear house with add-on rooms whose owner occupied each room as it was completed until finally settling in the last room. Of course, there is a practical scientific reason for all this expansion. Each chamber, or as many as needed, can be filled with gas to lift or lower the ammonite to a precise depth for feeding. No wonder the ammonite is prized as one of the earliest signs of intelligent life.

Once ammonites died and were buried in sediment, usually on ancient ocean floors, Mother Nature began to transform their shells into fossils, some of which are beautiful enough, when cut cross ways, to become art objects suitable for use as gems. Slowly, by a silica-immersion process, she broke down the ammonite’s calcium structure and replaced it with local minerals that both stained and solidified the shell. Think of Mother Nature as a kind of Andy Warhol, obsessively painting iconic logarithmic spirals the way Warhol did iconic Marilyn Monroe images, starting with the shell’s basic spiral design, then adding variation to each using different minerals for variety of color and texture.

Today, Madagascar is the biggest source of ammonite. Variety is so great from this cornucopia that there is no one peak of excellence for this fossil in gem slab form. My own favorites are pieces which exhibit remarkably opal-like iridescence, the result of micron-thick silica layering.
Russia is also a major provider of ammonite. We especially love its pyritized pieces where this particular iron sulfite has formed a kind of thick fool’s-gold leaf that make them look bathed in metal.

Morocco supplies ammonite with distinctive white and black, as well as black on black, spiral patterns that remind one of very elegant counter tops. Last but not least, Canada produces ammonites with the rich reddish-brown coloring of Madagascar plus areas of deep forest green.

At present, ammonite is used mostly for silver jewelry in pieces usually retailing for under $500. But Russell has made some extraordinary ammonite necklaces costing considerably more that could almost serve as breastplates. These remarkable pieces have a kind of ceremonial high-priestess look that suggests the archetypal pull of ammonite would have been present at any time when these art-relics were encountered.

Ammolite

Written by Modern Jeweler On May 2, 2013.

During the great 300-million-year flowering of marine life called the Paleozoic era, a squid-like animal known as the ammonite thrived in every ocean. This mollusk made its home in giant coiled shells similar to those of the chambered nautilus that we see today. Just like the dinosaurs that emerged later in this geologic age that began 500 million years ago, the ammonite eventually suffered a species wipeout.

Today, ammonites are found fragilely fossilized in various shales all over the world. Usually what remains are dull-colored agatized shell imprints in a host material. This imprint shows the increasingly larger quarters the growing animal built for itself in spiral fashion, walling off each new dwelling space from the previous one. Occasionally, when these aragonite shell molds are lined with nacre, they exhibit a pearly iridescence. The most iridescent and best preserved of these fossils go to museums, but some are used as pendants and brooches.

Now wouldn’t you think that the nacre-coated mollusk remains found on every former sea floor from South Dakota to Tibet would have become prime gem material sometime during the 200 million years since the Paleozoic era? After all, dinosaur bones are found in a gemmy petrified state. Why not gemmified ammonite?

Well, there is at least one place where ammonite shell metamorphosed into a bona fide gem material. Called, appropriately enough, “ammolite,” it is retrieved from shale found 20 feet or so below the ground at various spots throughout Alberta, Canada. The richest of these sites, located at Lethbridge, Alberta, was discovered in 1979 and ever since has been owned and operated by Korite Minerals Ltd., headquartered in Calgary, Canada. Since the Lethbridge deposit produces at least 90 percent of the world’s ammolite, Korite could be considered a De Beers for this gem, albeit a thimble-sized version that controls the market by default rather than design.

From Shell to Shellac

Unlike most ammonites, which died and left aragonite impressions of their outer casings in the sediment at the bottom of the ocean, ammolite was transformed from shell to gem altogether. Korite’s Pierre Pare explains how:

“The empty shell fell to the bottom of the ocean. Over millions of years, a concretion formed around the shell and it became a nucleus that was sealed off from the destructive effects of water and oxygen. As this nodule grew in size, it acted like a pressure cooker to re-mineralize and re-crystallize the ammonite.”

In a superb essay on ammolite published in the January 1986 Lapidary Journal, gemologist Fred Pough described the gem’s creation as a 70-million-year makeover, during which “the deeply buried [ammonite-shell] fragments have been squeezed, compacted and marinated” in a mineral-rich mudpack. Evidently, Alberta’s mudpack formula was unique because ammonites turned to ammolite aren’t as yet found elsewhere. Too bad. This shell-reborn-as-rough is glazed with a mother-of-pearl finish so superior to any latter-day variety Pough calls it “grandmother-of-pearl.”

Mining of ammolite is really long-odds excavation. Every year, Korite digs around 20 feet beneath the gravel at its Lethbridge site and extracts tens of thousands of nodules from the shale that it hopes contain cores of gem-quality material. But only 1 percent do. While these cores are, in effect, nuclei, don’t think of them the way you would the bead-nuclei of pearls. Instead, these nuclei have formed as thin layers inside hardened sediment. Because the original ammonite shell has disintegrated and transformed, ammolite shouldn’t be viewed as a fossil but, rather, as a reconstituted mineral.

Opal of the Sea

At first glance, ammolite could be confused with opal. But while it displays the same bright spectral colors as fine black opal, it does so in a far different way. Ammolite is, in essence, a laminate of crushed and re-crystallized aragonite on a backing of sediment that has hardened over eons into what gemologist Edward Gubelin called a “dark jasper-like rock.” When stones are cut, this aragonite layer is sawn off and polished. Since the aragonite usually re-crystallizes in discontinuous form, you see a scaly, random arrangement of sequin-like patches bordered by dark-brown host material.

The difference from opal becomes apparent when you turn ammolites in your hand. Although more brilliant and highly iridescent than opal, “the spectral succession is far less dramatic,” writes Pough. In short, ammolite colors shift far less than those of opal. Red, yellow and green seem the most common colors, blue and violet the least.

About 95 percent of ammolite is sold in doublet form: the ammolite is topped with a dome of transparent synthetic spinel covering a very thin layer of ammolite. Since ammolite has a hardness of only 4.5, the spinel top of the doublet also acts as a protective barrier. Rarer are solid ammolites, around 4,000 of which are cut every year. These sell for a significant premium.

Ametrine

Written by Modern Jeweler On May 2, 2013.

When in 1981 the gem trade got wind that ametrine, a combination of amethyst and citrine, could be created from amethyst in the lab by heating and irradiation, the warm welcome it had given this two-tone gem a year earlier became a cold shoulder.

The swift reversal of fortune for this two-tone purple and yellow quartz, and the drop in its price to levels almost equal to regular amethyst now seems unfair. Especially when the trade discovered that most, if not all, ametrine on the market is all natural, from an unusual mine in Bolivia.

Now this two-in-one quartz is staging a comeback, in part because it is championed by some famous gem sculptors, including Germany’s Bernd Munsteiner.

Unlike bi-colored tourmaline, which often combines popular green with equally popular red, ametrine combines popular purple with less popular brown and yellow. To make things worse, at the time ametrine was introduced, citrine had little of the popularity it enjoyed in the 1930s and 1940s or has since begun to enjoy again.

On top of this, demand for citrine was then narrowly focused on its deep brownish- and reddish-orange cognac colors. The gem’s lighter-toned yellows and golds were not nearly as appreciated as they are today. Since these latter hues were mostly what one saw in ametrine, the stone struck many jewelers as bland. So even without the taint of treatment, ametrine might well have bombed.

But its lack of prestige means that ametrine is the most affordable bicolor gemstone. It also means that the gem is an affordable medium for gem scuptors to work in, using the different color areas to add another dimension to their work.

Perhaps what ametrine needs to arouse interest from collectors is cutting as novel as its appearance. In some cases, carvings can show not only yellow and purple but also a warm peach where the two colors blend.

Ametrine can also show striking effects in stand-alone gem carvings. Munsteiner’s work in ametrine shows just how beautiful this affordable bicolored quartz can be: they are more art than adornment.

For jewelry use, ametrine is usually cut in an emerald cut to most clearly display the two-tone effect. When judging bicolor ametrine, look for the attractiveness of the two colors and their proportion. A half-and-half mix with a straight line between the two colors is considered best.


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