FEATURE STORY

Gem, mineral, and fossil all in one, this opalized clam shell from Australia has something for everyone. Harley Quinn collection; photo © Jeff Scovil. GREEN OBSIDIAN? Not. We bought a good-sized chunk (8.5 x 4.5 x 4 centimeters) of a bright, emerald-green glass from a young Brazilian dealer we are convinced was completely honest but a mite misdirected. When we expressed our doubt about the natural, volcanic origin of the glass, he told us it was a new occurrence of gem obsidian from Brejino, Bahia, Brazil. He also volunteered that he had never heard of obsidian from Brazil, and certainly not from Bahia, which is a long way from the Andes, famous for their spectacular volcanic peaks. The piece we selected showed prominent devitrification features, such as whitish, iridescent coatings on some surfaces. It was also almost as filled with bubbles as Peking glass, a term with which bead collectors are familiar and which refers to an old Chinese glass noted for its profusion of bubbles. Nearly as green as the so-called Mount St. Helen's glass, this emerald-green glass is really pretty, but we don't think it's obsidian. (Mount St. Helen's glass was supposedly made by melting the volcanic ash spewed out by the cataclysmic eruption of Mt. St. Helens in Washington in 1980, a claim refuted by experiment: glass made from the ash in these experiments was black, not green.) We suspect that our Brazilian "emerald obsidian" is possibly a slag, or an assay button. Often found in the vicinity of old mining towns, these "buttons" are byproducts of assaying in which ore samples are melted to determine their metals content. When the metals separate from the ore (and from the flux used to facilitate melting), what's left fuses into a glass blob that looks vaguely like a button, hence the term. Always a silicate glass, this glass is frequently misidentified as obsidian, which is a naturally occurring silicate glass. The buttons come in a wide variety of colors, some of which are pretty enough to cut interesting gemstones. Assay buttons are often called obsidianites to obfuscate their manmade origin. Sometimes the glass slag from small smelting operations also yields good cutting material, as many rockhounds today are aware. From the early 1800s to 1912, some 265 iron furnaces produced glass slag in parts of Illinois, Kentucky, and Tennessee, in the area between the Cumberland and Tennessee Rivers, and rockhounds still find the glass today. According to one who should know, J.T. Pittman (1985, 33), "When you cut and polish it [the slag] properly . . . it can equal agates in luster and beauty." We don't know if the green Brazilian glass is a slag or an assay button, but with the presence of numerous round bubbles and the absence of any evidence of flowage and such evidence as its emerald-green color, we've pretty well ruled out the possibility of it being obsidian. Still, it's such a luscious green that it would make interesting cabochons and lovely beads. MAGENTA DENDRITE? We discussed the relative shades and stability of aniline-dyed agates with Michael Siegal, who imports tons of Brazilian agates. He said that it is getting difficult in Brazil to buy undyed polished agate slabs since the dyed ones always outsell naturally colored ones to the general public, and the more garish, the better. Then he gleefully pointed out a slab with a great dendrite (a treelike pattern; see "Nature's Line Drawings," Lapidary Journal, February, 2002) that had been dyed a bright magenta -- a very odd choice since to knowledgeable collectors a fine dendrite would be worth much more if the agate were naturally colored. Since we collect oddball examples, fakes, and otherwise tinkered-with specimens as well as fine unadulterated ones, we were thrilled when he priced this agate for us at the cheap rate dyed agate generally goes for. If we grew tired of the unbelievable color, he told us, we could "just leave it in the sun for two to three weeks and the offending color will have dissipated." We wrapped it in the most light-proof materials we could find and placed it in the very bottom drawer of the cabinet that holds our most treasured agates. Any visitor will be shown it for only the merest fraction of a nanosecond. We do not want this horrid color to fade away. CONTINUING TREND. Natural forms or forms produced by people that resemble natural forms have an appeal in the market that just continues to expand. It was startling, but at the AGTA [American Gem Trade Association] show, dealers in the traditional stones such as diamond, ruby, sapphire, and emerald were easy to browse. Even the pearl dealers, and there were lots of them at all the gem shows, were not very crowded in spite of the great abundance of pearls at much lower prices than we have ever seen before. However, we found it difficult to elbow our way to the booths of dealers who specialize in unusual cuts and unusual stones -- with and without a little human intervention to add variety to their colors. Some of the new trends take a bit of getting used to -- thin-film coatings on drusies that turn them iridescent pink and so on -- but we are slowly coming around. As mineral collectors, we were originally purists about not tampering with a stone's color or shape. Slowly it dawned on us, though, that progress in the gem world has to do with experimenting with and developing new shapes and better colors. The slow development of the art and science of faceting diamonds has to be viewed as progress, even though in our heart of hearts we still much prefer a well-shaped natural diamond crystal -- but let's face it, most natural diamond crystals are not particularly attractive to the eye. With their sparkling crystal coatings, drusy gemstones are among the most popular of the unusual gems among designer jewelers. Rare Earth Gallery collection; photo © Jeff Scovil. COLORFUL GYPSUM CRYSTALS. New and shocking, but they will probably sell well. A dealer at the Executive Inn had a lot of 33 flats of gypsum groups whose natural color would have made them a hard sell, but these had been dyed fluorescent orange, green, red, and yellow. They were easily noticed even at a considerable distance, especially when the sun came out, which it did occasionally this year. AGATE CARVINGS Since shortly after the fall of the Iron Curtain, we've been seeing splendid dendritic agate pieces, most as cabs and small slabs cut and polished in Russia. The best of this material ranks with the best dendritic agate in the world, but up until this Tucson we hadn't seen any really creative lapidary work utilizing this marvelous material. However, Dr. Margarita I. Baneeva, a gemologist from New York, displayed carvings in Kazakhstan agate by Felix Ibyagimov of St. Petersburg that showed a wondrous creativity and feel for this splendid agate. The veined leaves were particularly impressive. FOSSIL CORAL As promised in LJ's Tucson preview ("Living Up to the Hype," December, 2001), Betty Sue King of King's Ransom at AGTA had a totally new gem that was particularly suited for men's jewelry: sting-ray coral. With a black background and a three-dimensional white "net" of coral, the stone looks vaguely like a petrified honeycomb. According to Mark Castagnoli of Placer Gold Design in Vancouver, British Columbia, Canada, who collected it "on a remote island off the coast of Prince of Wales Island in south-east Alaska," it is an extinct coral from the Silurian period of the Paleozoic era. "When cut and polished on the horizontal," he told us, "the material has a highly detailed honeycomb pattern of hexagons ranging in size from one to three millimeters. When cut on the vertical, the structure is of segmented ovals." NEW CUT We bumped into Dr. Joel Arem, best known as the author the Color Encyclopedia of Gemstones, who was rushing through the upper hall at the Tucson Convention Center. He slowed long enough to give us a quick glance at a fabulous yellow bytownite feldspar gem from Mexico, for which he has developed a new cut, trademarked Virtual Reality. The cut really brings out the beauty of this unusual feldspar that occurs as large phenocrysts (crystals that had a chance to grow slowly and large in the liquid basalt magma before it was chilled to a fine-grained black lava rock by being poured out on the surface of the ground). Most feldspar is about 6 in hardness; Arem reports that this feldspar tests out as closer to 7. Look in Lapidary Journal for more about this new cut as it becomes available. EMPTY YOWAH NUTS Rod Griffin, who owns an opal mine at Yowah in Queensland, Australia as usual had very fine "Yowah nut" opal with marvelous play-of-color. What turned out to be most interesting to us, however, were the "nuts" that had little or no opal in them, but when broken open were hollow. If you had to name them, they would probably be called ironstone (sand cemented by various iron oxides and hydroxides). We're sure that if the metaphysical crowd gets wind of these fascinating formations, they'll quickly come up with a better name and lots of marvelous attributes. Since these items are apparently quite abundant, they'll probably end up becoming a staple of many shops.

Si & Ann Frazier

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Si and Ann Frazier have been in the gem, mineral, and jewelry supply business since 1965 and are currently working on The Encyclopedia of Quartz. Si has also taught gemology, mineralogy, and related courses at the university level, and is a lifelong rockhound.

 

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