Dreamy Prasiolite
by Diana Jarrett, GG RMV

The ultimate dream stone for gem collectors would be this: distinct attractive color, available in large carats, eye clean, and cheap. Too good to be true? Not if you’re on the trail of prasiolite.

This diaphanous gemstone seemingly appeared from nowhere— and is further mystifying by its many names. Prasiolite, boasts various alternate monikers; vermarine, mint quartz, green amethyst, lime citrine, and the self explanatory green quartz.

Some online mineral sites declare all prasiolite to be enhanced amethyst or citrine quartz. In fact, geologists have found modest deposits of naturally occurring transparent green quartz near hot springs. One might speculate that those mineral waters are also iron rich. The small alluvium located in nearly inaccessible areas rendered these extraordinary finds unsuitable for commercial use.  The Smithsonian Institute has crystal fragments of natural green quartz from Brazil dating to 1884. At Tucson this year, rare gems specialist K & K International of Falls Church, Virginia brought specimens of the natural material faceted into oval brilliants of .40 carats which have been in their collection for years.

Commercial prasiolite occurs when dull amethyst or citrine undergoes heat treatment in the presence of iron, transforming the quartz into a cool leek or celadon green. Exceptionally clean crystal rough is selected for this process, even though quartz is by nature relatively inclusion free. Clean rough assures even color distribution. Most prasiolite comes from the Montezuma mines at Minas Gerais, Brazil.  More recently it’s found in the United States, but Brazil is certainly the main channel for the material.  It’s not their biggest money maker, but Brazilian suppliers striving for greater presence in the global loose gem market, make prasiolite a priority. The impression is that prasiolite is the new-kid-on-the- block, in reality that process has been performed since the 1950's. The term ‘greened amethyst’ appeared thirty years ago in American Mineralogist Volume 62, 1977– “A Unique Green Quartz.”

The abundant material is often cut in large carats and with complex cuts to force the best color from the pale stone. Briolette, concave, and checkerboard crown cuts are favored, intensifying the hue which often appears pallid in emerald or baguette cuts. Exceptions to this are seen in finished goods featuring several prasiolite together or paired with other green or pastel colored stones.  Current wholesale prices range from $3 to $6 dollars per carat for well cut stones of good color. In Tucson, a Brazilian buyer at an American vendor’s booth remarked that it’s cheaper to buy prasiolite in the States than in Brazil, citing wholesale prices of $7 to $8 per carat for small quantities there. Cut goods sold in bulk with less bailable color saturation run as little as $1 per carat. But don’t expect their pricing to remain this low.

As expected with enhanced gemstones, a range of colors and tones are found in prasiolite. Only thirty percent of each batch of quartz undergoing this treatment transforms into the cool green color.  Without proper identification, some of it might be mistaken for green beryl or a light toned green tourmaline. Dealers who use specific gravity testing in the field for gem identification, know the similar SG of beryl (2.6-2.9)  and quartz (2.65) could lead to a case of mistaken identity.  Nevertheless, prasiolite’s RI verifies it as quartz, reading 1.54 - 1.55 on the refractive index, making the separation conclusive.

At the Atlanta Jewelry Show, Darling Imports, Inc., of Hampton Georgia included prasiolite in their offerings, some of which exhibited dusky undertones. The dealer explained that his were smokey quartz having undergone the heat treatment. The majority of these prasiolite possessed attractive medium tones, a characteristic designers look for in large carats. The occasional maverick, displayed a more brownish green color, signaling its origin.

Customarily, ubiquitous low-cost stones are consigned to inexpensive ‘bridge’ jewelry, that parallel universe between costume and fine goods. However, pretty prasiolite fuels the imagination of fanciful designers driven by inspiration in their ingenious styling—which is why one sees a stone that sold for $3 per carat turning up in  $5,000 designer goods. With custom jewelers adding prasiolite to their repertoire, wholesale prices are bound to reflect this fondness.

When buying prasiolite, keep in mind that well proportioned classic cuts fare better over time. As for color–  the darker the better is the rule. Examine stones from the pavilion side for even distribution of color and clarity.  This dream stone has yet to realize its full potential.