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Fall 1991 Gems & Gemology Gemological Abstracts

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Fall 1991 Gems & Gemology Gemological Abstracts REVIEW BOARD - Barton C. Curren Neil Letson Lisa E. Schoening Rose Tozer lopanga Canyon, California flew York, New York GIA, Santa Monica GIA, Santa Monica Emmanuel Fritsch Loretta B. Loeb James E, Shigley William R. Videto GIA, Santa Monica Vasalia, California GIA, Santa Monica GIAj Santa Monica Patricia A. S. Gray Shane F. McClure Christopher f! Smith Robert Weldon Venice, ~alifornia~ Gem Trade Lab, Inc., Santa Monica Gem ~radeLab, Inc., Santa Monica Los Angeles, California Karin N. Hurwit Elise fl. Misiorowski Karen B. Stark Gem Trade Lab, Inc., Santa Monica GIA, Santa Monica GIA, Santa Monica Robert C. Kammerling Gary A. Roskin Carol M. Stockton GIA, Santa Monica GIA, Santa Monica 10s Angeles, California , COLORED STONES AND is Ba4(Ti,Nb,Fe)oO16(Si4012)Cl. A brief description of ORGANIC, MATERIALS the occurrence of baotite is presented, although no information is included on its abundance. /Es Baotite-A new gemstone in Baiyun Ebo, Inner Mon- golia. Sun Weijun and Yang Ziyuen, Abstracts of Emeralds from Colombia (Part 2). C.Bosshart, fournal of the 15 th General Meeting of the International Gemmology, Vol. 22, No. 7, 1991, pp. 409-425. Mineralogical Association, June 28-July 3, 1990, Part 2 of this trilogy on Colombian emeralds includes a Beijing, China, pp. 688-689. review of crystal size and morphology, chemical compo- Baotite is a brownish black to black translucent mineral sition, causes of color, physical and optical properties, with a semi-metallic luster and a Mohs hardness of 6 and microscopic features. It is interesting to note that that could potentially be used as a gem material. It is the author, contrary to one commonly held notion in newly discovered from the Baiyun Ebo rare earth-iron Europe, acknowledges emeralds colored largely by van- ore deposit in Inner Mongolia. Its chemical composition adium. Colon~bianemeralds, with an average Cr:V ratio of 3:1, fall in the middle of the range of chromophore composition for emeralds in general. Iron content of Colombian emeralds is relatively low, and other possible chromophores are absent or insignificantly low. Optical This section is designed to provide as complete a record as absorption spectra, illustrated by unretouched spec- practical of the recent literature on gems and gemology. Articles are selected for abstracting solely at the discretion of the section trophotometer curves, are related to the chemical causes editor and her reviewers, and space limitations may require that we of color and to the renowned fine color of Colombian include only those articles that we feel will be of greatest interest to emeralds. our readership. The discussion of microscopic features that con- Inquiries for reprints of articles abstracted must be addressed to cludes this article covers fluid inclusions, mineral inclu- the author or publisher of the original material. sions, internal growth characteristics, and color zoning. The reviewer of each article is identified by his or her initials at the Three pages of color photomicrographs illustrate the end of each abstract. Guest reviewers are identified by their full features discussed. names. Opinions expressed in an abstract belong to the abstracter and in no way reflect the position of Gems & Gemology Ifound part 1 of Mr. Bosshart's three-part series to be or GIA. commendable and readable, and I have not been disap- pointed by part 2. Moreover, the discussion in part 2 @ 199 I Gemological Institute of America provides information on emeralds other than those of Gemological Abstracts GEMS & GEMOLOGY Fall 1991 195 Colombia, making the article of even broader interest Gemmology Study Club Lab Reports. G,Brown, S. M. B. and gemological value. It was, however, mildly frustrat- Kelly, R. Beattie, and H. Bracewell, Australian ing not to have the bibliography printed with the article Gemmologist, Vol. 17, No. 8, 1990, pp. 325-332. in hand (an editor's note advises that the full bibliogra- This series of brief reports covers a number of interesting phy was published with part 1). CMS gem materials. First described is a 1.12-ct crystal frag- ment from central Queensland that consists of a ruby core surrounded by hexagonally banded grayish blue to An examination of chrysoprase from Goias, Brazil. R. C. bluish to purplish sapphire. Next covered is gem-quali ty Kammerling, J. I. Koivula, and E. Fritsch, Austra- stichtite, a rare, chromium-containing mineral from lian Gemmologist, Vol. 17, No. 8, 1990, pp. northwest Tasmania. 313-315. The next, and longest, of the entries covers a suite of The authors studied specimens of chrysoprase that were jewelry set with emerald-cut stones that resemble "pad- reported to have originated in a galena mine near paradscha" sapphires. According to the investigators, Niquelandia, Goiis, Brazil. The gemological properties these stones were actually flame-fusion synthetic yel- were found to be consistent with those previously low sapphires "coated by a thin layer of surface diffused reported for chrysoprase chalcedony. X-ray fluorescence synthetic ruby." It is interesting to note that the owner of spectroscopy revealed that silicon and nickel were the the jewelry had purchased it in Kashmir. only elements present in significant amounts. Compari- This is followed by an entry on two glass imitations, son of these samples with Australian chrysoprase indi- the first resembling aquamarine and the second com- cated that features are similar except for the intense posed of a photosensitive glass that changes from color- absorption in the Australian material, which correlates less to dark brown after a 15-second exposure to a 150- with its more saturated color. watt incandescent bulb. Although the authors have observed that chrys- Also covered are green beryls from Harry's Mine oprase is typically inert to U.V radiation, the Brazilian near Torrington, New South Wales (with a good descrip- material fluoresced a moderate greenish blue to long- tion of their gemology and inclusions); an aventurescent wave U.V, with a weaker reaction to short-wave U.V quartz that reportedly originated from a site near In- There was no phosphorescence to either wavelength. verell, New South Wales, and resembles aventurescent Maha Smith feldspar; and pit glass from Sri Lanka. RCIZ Editor's Note: Diffusion treatment actually diffuses a Fossil mammoth ivory: A new choice for jewelers. R. layer of color into the stone and is not a coating per se. Weldon, Jewelers' Circular-Keystone,Vol. 162, No. However, recutting can remove the color. 8, August 1991, pp. 154-156. Since the U.S. banned the import of elephant ivory in Gemmological study on Eonyang amethyst from Korea. 1989, fossilized mammoth ivory has become a favored - Won-Sa Kim, Abstracts of the 15th General Meet- and legal-alternative. The permafrosts of Alaska and ing of the International Mineralogical Associa- the Soviet Union are sources for this ivory, which is tion, June 28-July 3, 1990, Beijing, China, pp. thought to have lain preserved for 20,000 to 40,000 years. 678-679. This type of ivory has been used by the Athabascan Amethyst that occurs in geodes is found in the Eonyang Indians, Eskimos, and other Alaskans for thousands of Granite near the southern part of the Korean peninsula. years. According to Al Allen of Alaska Jade and Ivory The amethyst develops as an epitaxial overgrowth on Works, Soldotna, Alaska, 20,000 Indians currently make earlier-formed smoky or colorless quartz. Fe, Mg, Ca, a living from fossilized ivory. and Cu occur as trace elements in the amethyst in Depending on the minerals absorbed, fossilized quantities up to 6 ppm. Various solid inclusions (hema- ivory can occur in different colors: It has been found in tite and perthite feldspar) and fluid inclusions (both dark blue, black, brown, and green, as well as in various liquid and gaseous) that occur in the amethyst were shades of cream. Besides strength of color, the best way studied by several analytic methods to reveal the condi- to distinguish between fossilized ivory and modern tions of amethyst formation. IES elephant ivory is from the engine-turn effect: The V-shaped crossing of lines in fossilized specimens forms acute angles of 90' versus the angles of 120' or more On the genesis of charoite rocks. N. V. Vladykin, seen in modern elephant ivory. Abstracts of the 15th General Meeting of the Other animal ivories and products exist such as International Mineralogical Association, June walrus, narwhal, animal bone, horn, antlers, and chem- 28-July 3, 1990, Beijing, China, pp. 689-690. ically treated coral. For those uncomfortable about The geologic occurrence of this ornamental gem mate- wearing ivory of any kind, doum palm, orozo nuts, and rial in the Soviet Union appears to be unique. Charoite is even plastic are available. KBS found in the Murun massif, a large body of layered 196 Gemological Abstracts GEMS & GEMOLOGY Fall 1991 ultrapotassic-alkali rocks that have been age dated at shell dredged off the coast from Noosa, some 100 km 120-160 million years. A number of unusual rock types north of Brisbane, Queensland. are represented in this layered sequence, among which is The authors preface their description of the "pearl" charoite. These unusual rocks are thought to have with a detailed description of the host shell, Melo crystallized from an ultrapotassic lamproite magma. amphora. The "pearl" itself weighs 68.97 ct, measures Inferences are presented on the temperatures and other 22.8 mm x 20.6 mm, and is slightly pinkish orange, conditions of crystallization. IES nonnacreous, and slightly pointed on one end. It displays a distinctive "flame" pattern similar to that seen on so- called conch "pearls." Magnification reveals that the Mineral associations of corundum-bearing marbles and smooth porcelaneous external surface is covered with a the problem of ruby genesis.
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