REVIEW BOARD Emmanuel Fritsch Marv L. Johnson Himiko Naka University of Nantes, France GIAG~~Trade Lab, Santa Monica Pacific Palisades, California Charles E, Ashbaugh Ill Isotope Products Laboratories Michael Gray A. A. Levinson Gary A. Roskin Burbank, California Missoula, Montana University 01 Calgary European Gemological Laboratory Calgary, Alberta, Canada Los Angeles, California Andrew Christie Patricia A, S, Gray Loretta B, Loeb James E. Shigley GIA, Santa Monica GIA, Santa Monica Missoula, Montana Visalia, California Carol M. Stockton Jo Ellen Cole Elise B. Misiorowski GIA, Santa Monica Professor R. A. Howie GIA, Santa Monica Alexandria, Virginia Royal Holloway Rolf Tatje Maha DeMaggio University of London Jana E. Miyahira Duisburg University GIA Gem Trade Lab, Santa Monica United Kingdom GIA, Santa Monica Duisburg, Germany COLORED STONES AND Townsendl. In disagreement- with traditional theories of ORGANIC MATERIALS opal formation, Len Cram offers a surprising new model, based on ion exchange, that he demonstrated by growing Cretaceous mushrooms in amber. D. S. Hibbett, D. synthetic opal out of "opal dirt" in a bottle in just three Grimaldi, and M. J. Donaghue, Nature, October 12, months. Jiirgen Schutz describes the long history of 1995, p. 487. Mexican opals, their varieties, and the present mining sit- Recently, two mushrooms were discovered in amber of uation. Jochen Knigge recounts the history and produc- Turonian age (90-94 million years old, mid-Cretaceous] in tion of opals from Pedro 11, Piaui, Brazil. Klaus Eberhard central New Jersey. One specimen is nearly complete, with Wild portrays another important locality-Kirschweiler, an intact cap, distinct gills, and a central stalk (itis the old- near Idar-Oberstein-which was (and perhaps still is] one est known such mushroom, by about 60 donyears); the of the most important centers of opal fashioning and other is a wedge-shaped fragment of a mushroom cap. Both trade worldwide. mushrooms resemble modern common leaf-litter and Jiirgen Schiitz explains the factors that determine the wood-decayer species, and both were growing on a cedar (a price of an opal (localityof origin, body color, play-of-color, member of the Cupressaceae family). ML/ Opal. extrdapis, No. 10, 1996, 96 pp. [In German]. This section is designed to provide as complete a record as prac- Opal is the subject of another extraLapis, an issue of tical of the recent literature on gems and gemology Articles are selected for abstracting solely at the discretion of the section edi- Lapis magazine that is devoted entirely to one gemstone. tor and his reviewers, and space limitations may require that we Following a comprehensive introduction by Edward include only those articles that we feel will be of greatest interest Giibelin, a series of articles provide information on all to our readership. important aspects of ths colorful gem. Inquiries for reprints of articles abstracted must be addressed to An article by Max Weibel explains the origin of play- the author or publisher of the original material. of-color. Two other papers describe Queensland's boulder The reviewer of each article is identified by his or her initials at the opals, their forms, production, and prospecting methods end of each abstract. Guest reviewers are identified by their full (WilsonCooper and Barry J. Neville); and the geologic set- names. Opinions expressed in an abstract belong to the abstrac- ter and in no way reflect the position of Gems & Gemology or GIA. ting and processes that led to opal formation in the sedi- 0 7996 Gemological Institute of America ments of Australia's Great Artesian Basin (Jack Gemological Abstracts GEMS & GEMOLOGY Fall 1996 225 pattern, cut, size). Even with these criteria, it remains dif- ore, at a valuation of $58.17 per carat. Bulk sampling is ficult to know how much a harlequin opal is really worth. proceeding at the A-154 South, A-154 North, and A-21 Three additional articles provide information on opal lzimberlites. MLf nomenclature (Jurgen Schutz and Manfred Szykora); dou- blets, triplets, and opal mosaics (Karl Fischer]; and synthet- Diamonds everywhere. C. Koeberl, Nature, November 2, ic opals and opal simulants (Manfred Szylzora].The volume 1995, pp. 17-18. concludes with a description of opalized fossils: snails, On Earth, diamonds usually occur in rocks derived from mussels, belemnites, and even dinosaurs [Alex Ritchie and the mantle. They are thought to have formed from fluids Brigitte Szylzora). or melts in the upper mantle at "immense" temperatures This extraLapis also contains short descriptions of and pressures, probably-according to Mr. Koebcrl-dur- smaller opal sources [Denmark, Honduras, Indonesia, ing several diamond-forming events early in the Earth's Mali, Saxony, Slovakia [formerly Hungary], Turkey, and history. Diamonds have also been produced, directly on the United States]; an opal glossary; and the stories of the the Earth's surface, during meteorite impacts; such dia- Hope and El hila Azteca opals (by John S. White). Also monds may have formed, at least in one case [Ries described is an extraordinary opal necklace that Queen Crater), from the vapor phase. Diamonds found in iron Elizabeth I1 was not given as a coronation present (by meteorites and ureilites [another variety of meteorite) Helmut Weis]. Two stories tell us how Australian aborig- were formed by shock from graphite or an~orphouscar- ines explain the origin of opals. bon, probably in the meteorite and not after it arrived on A volume about opals with words only (in this case, the Earth. Nanometer-size diamonds have been found in German) would be utterly frustrating. In this edition, chondritic meteorites, associated with noble gases however, the stunning beauty and incredible variability [xenon, argon, etc.] with unusual isotopic compositionsj of opals is illustrated throughout the entire volume by these came from interstellar or presolar events very early wonderful color photographs. RT in the history of the solar system. Small diamonds have also been found in clays marking the boundary of the Zur Entstehung der sternfoermigen Achate in sauren Cretaceous and Tertiary periods, which has evidence of a Vulkaniten. Eine modifizierte Bildungstheorie (The large impact; their carbon and nitrogen isotopes point to origin of star-shaped agates in acidic vulcanites. A an origin within the impact event or the resulting fireball. modified theory of formation). R, Rykart, Der Polycrystalline diamonds up to 1 cm, discovered in Aufschluss, Vol. 46, 1995, pp. 33-36. impactites at a few Russian and Ukrainian impact stnrc- It has generally been believed that agate formation in rhy- tures, also appear to be crustal in origin. Impact-produced elites and porphyries takes place at high temperatures. diamonds are very different from microdiamonds found Recent research by M. Landmesser has shown that agate in high-grade inctamorphic rocks. may form in other types of rocks at lower temperatures. In Also rare and unusual are polycrystalline black dia- this article, Mr. Rylzart proposes a new theory for the for- monds, called carbonados. No carbonado diamond has mation of star-shaped agates in lithophysae (e.g., thunder ever been found in situ in a rock. Possible origins include eggs] in rhyolitic vulcanites. The basic idea is that the carbon subduction in the mantle, shock metamorphism gaseous bubbles in the magma contract to form polygonal during impact, or irradiation of organic matter; vapor- cavities because of dropping gas pressure during cooling deposition may also be a candidate. MLJ near the Earth's surface. Subsequently, monomer H4Si04, dissolved in the water that invades the cavities, fills them Diamonds: Wyoming's best friend. Geotimes, Vol. 41, with chalcedony and quartz. The surrounding rhyolite No. 2, February 1996, pp. 9-10. devitrifies and hardens, forming the well-known quartz porphyry kills. RT The first diamond mine in Wyoming is about to begin pro- duction, and many more lumberlites and lamproites in the DIAMONDS region may contain diamonds, according to W. Dan Hausel of the Wyoming State Geological Survey. Redaurum Red Aber Resources Ltd. Diamond Industry Week, February Lake has just finished construction of a 140-ton-per-hour 26, 1996, p. 3. ore-processing ~LUfor the cornpanyls Kelsey Lalze di'mond Aber Resources has announced results from drill cores at property, along the Colorado-Wyoming state line; several A-418, one of their lumberlite pipes in the Northwest gem diamonds, up to 14.2 ct, already have been recovered Territories, Canada. Nineteen tons of ore in a large-diain- from this property. The Colorado-Wyoming lumberlite eter (6 inches, about 15 cm] core drilled through 367 m of province includes more than 100 lumberlite intrusives, one lumberlite yielded 83.1 carats of diamonds-4.3 carats per of the world's largest lamproite fields, and dozens of unex- ton of ore-with individual stones between 0.025 and 3 plored geophysical and geochemical anomalies. More than carats. The largest "gem" diamond weighed 2.2 carats. 120,000 diamonds have been recovered from this area in the The A-418 pipe is estimated to contain 15 million tons of last 20 years. ore to 650 in depth; the grade is similar to that of the A- No history of diamond mining in Wyoming is con~plete 154 South lzin~berlite,which showed 4.5 carats per ton of without mention of the "Great Diamond Hoax of 1872." A 226 Gemological Abstracts GEMS & GEMOLOGY Fall 1996 sandstone outcrop was salted with 10 pounds of uncut dia- The authors note the paucity of published