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January-February 2009

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Letters


SOUR GRAPES FROM CHINA
For more than fifty years, agate collectors have found fascinating botryoidal agate, informally called “grape agate,” from the Jurassic Curtis Formation in Emery County, Utah. Zenz shows a good example on page 13 in his beautiful book titled Agates, although he does not list the locality. So when “grape agates on steroids” appeared at the Tucson Show in 2008 and consistently thereafter on eBay during the past year, we were amazed and bought a few. China (or Mongolia, which in some cases is given as the location) has done it again; not only does it produce incredible minerals, but now also the best grape agate in the world. Our excitement, however, was short lived.

The first thing we noticed were inconsistencies between the individual agate spheres and the color patterns. Vague bands of colors continue across the specimens in places and seem to have little relation to the spheres. Still other spheres are tinted on the edges, which could probably be considered normal coloration. But upon close inspection, the overwhelming problems are the ubiquitous accurate grooves on the spheres and the obvious grooves at the base of every sphere. These are telltale signs left by a carver who did not take the time to remove them. Moreover, the sizes of the individual spherulites are limited to a few specific radii, suggesting that diamond tools of fixed size were used in their manufacture. Thus, we determined that every piece is bogus! Someone spent a lot of time transforming ordinary chunks of agate into grape agate! The quality of workmanship is variable, with some clusters made from relatively flat pieces of agate rough and showing conspicuous lapidary marks, while others are decidedly three dimensional and carved more carefully. Photographs on eBay show specimens that appear slightly wet or that were somehow made shiny, rendering the cut marks difficult to see, even in the close-ups.

Our next question: Are these naturally occurring grape agates that have been enhanced, or are they merely pieces of chalcedony or banded agates that have undergone rather extreme transformations? Or is this actually agate at all? To find an answer, we sacrificed a specimen and made a thin section. The internal structure clearly displays characteristic agate textures with radiating bundles of chalcedony fibers, obvious growth boundaries, and concentric banding. However, the relation of these internal textures to the surficial spherulitic growths is completely missing. Thus, the carved agate could not have once had a botryoidal habit.

The sale of these specimens would not have been a problem except the specimens were not advertised as carvings. A quick trip to the Mindat website’s “Fakes, Frauds, and Marketing Ploys” section revealed that several people had already spotted these fakes and admonished anyone stupid enough to ever be fooled by such poor-quality forgeries. This made us feel much better. The peddlers on eBay have since changed their felonious descriptions from “natural high-quality material, grape-cluster agate” and “Chinese beautiful ornament: agate rockery grape” or “natural beautiful brown agate grape ball shape” to more truthful comments, such as “Note: the stone exterior is exterior making,” or even “manmade racemoseshape agate,” as listed by one honest seller. Another observation we've made during the past few months is the considerable inflation that these grape agates have undergone, with starting prices for larger pieces approaching $500 (which does not include a substantial shipping cost).

Having said all of this, we still like our grape-agate sculptures and have prominently displayed them. When people ask, we have a great time telling them the story of Chinese grape agates. Who knows, maybe China really does have the real McCoy out there somewhere.

Richard Dayvault, Grand Junction, Colorado
 Dan Kile, Littleton, Colorado


EDUCATIONAL AWARD
At the annual Tucson Gem and Mineral Show (TGMS), the Friends of Mineralogy (FM) recognizes exhibits that help explain some aspect of mineralogy. The “educational awards” are in addition to awards for best article in Rocks & Minerals and other periodicals. To be considered for an award, an exhibit must have some special instructive feature as well as maintain an aesthetically pleasing display, concurrent with the high standards of the TGMS. Two certificates are awarded, one for private exhibitors and another for museums. The winners are honored at the Saturday night TGMS banquet. Permanent plaques with the winners’ names are featured in the FM display case during the show every year.

Instructive exhibits help the hobby grow, underline its scientific basis, and inform the public of its relationship to everyday life. Readers who exhibit at Tucson are asked to seriously consider featuring educational themes for their displays.

Recognized at the 2008 show were Dr. Georg Gebhard (for the third time) and the Gemological Institute of America.

Virgil Lueth, President
Friends of Mineralogy
Socorro, New Mexico


HEMISPHEROIDAL FLUORITES FROM INDIA
I read with interest John White’s article on botryoidal fluorite in the July/August 2008 issue. I was pleased that he interpreted these as products of radial growth of a polycrystalline aggregate from a common center of growth. I offered a similar opinion in a note in the Lithographie issue on fluorite, admittedly on the basis of crystal growth theory rather than on any specific observations.

John indicates in his article that he had only weak observational evidence for his conclusion of radial growth, in good part because fluorite is isotopic and shows no useful texture in thin section and crossed polarizers.

After some initial correspondence, John sent me a sample to experimentwith. I was able to cut and polish a section close to the geometric center of a hemisphere. I then etched the polished surface in dilute hydrochloric acid for about two days. The etching preferentially attacked the boundaries between the individual crystal grains that made up the hemispheric aggregate. The digital image pictured here shows a clear radial texture.

The etched section was not cut precisely through the center of growth nor parallel to the rays of individual crystals. Consequently, rather than seeing a series of rays emanating from a common center, one sees a series of radially arranged, elongated polygons. Nevertheless, it appears clear from this experiment that at least this hemisphere was a result of radial competitive growth of many crystals from a common center of growth.

R. Peter Richards
Oberlin, Ohio

I enjoyed John White’s article on hemispheroidal fluorites from India in the July/August 2008 issue. Because New Mexico was not listed in the occurrences of botryoidal fluorite, I thought readers would be interested in some noteworthy (if not well-known) occurrences here in the “Land of Enchantment.” Below is a listing of some localities that are generally unknown in the mineral collector community.

Botryoidal Fluorite in New Mexico

*Small Fry prospect: Rio Arriba County. Lavender, translucent botryoidal hemispheres to 4.5 cm that culminate in very small cubes on the surface. Found in veins in Tertiary volcanics and are associated with barite. Negligible fluorescence.

*Sierra Blanca: Lincoln County. Cream-colored, opaque botryoidal hemispheres to 2 cm perched on gemmy smoky quartz crystals. Cream-colored fluorescence with green undertones
(LW).

*Lucky Irishman prospect: Burro Mountains, Grant County. Pale to dark green, opaque hemispheric masses to 5 cm. Found with calcite scalenahedra pseudomorphed to quartz and with a purple fluorite substrate. Bright violet fluorescence (LW).

* “Bootlegger” mine: Cuchillo Negro district, Sierra County. Undetermined mine name but has been dubbed “Bootlegger” by local collectors. Botryoidal, green and some purple, subtranslucent masses to 8 cm. Violet fluorescence.

*An additional fluorite occurrence of interest is in the Bluewater area of the Zuni Mountains near Gallup, where fluorite veins are found at a small prospect in Precambrian granite. The veins are up to 2 cm thick and, when split, show concave and convex surfaces that appear to be botryoidal, with intergrown hemispheres to 1 cm. When broken, the “hemispheres” reveal an octahedron with curved faces at the core. As the octahedron grew, the faces became more curved, resulting in a surface that resembles a hemisphere! Very interesting stuff.

Ray DeMark
Albuquerque, New Meixco

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