• Abstract and Figures
• Public Full-text

TABLE OF CONTENTS 79 EDITORIAL Carlsbad: A New Home for GIA and Gems & Gemology Alice S. Keller FEATURE ARTICLES 80 Update on Emeralds from the Sandawana Mines, Zimbabwe pg. 99 J.C. (Hanco) Zwaan, Jan Kanis, and Eckhard J. Petsch 102 Modern Diamond Cutting and Polishing Akiva Caspi 122 Gem Rhodochrosite from the Sweet Home Mine, Colorado Kimberly Knox and Bryan K. Lees pg. 115 REGULAR FEATURES 134 Gem Trade Lab Notes 142 Gem News 153 Thank you, Donors 154 Book Reviews 156 Gemological Abstracts 163 Guidelines for Authors ABOUT THE COVER: Although rhodochrosite had long been known to the gem and jewelry community as a massive, pink ornamental material, recently some attractive transparent orangy pink to red rhodochrosites have become available as faceted gems. Many of the transparent rhodochrosites in the gem market today are from the Sweet Home mine near Alma, Colorado. Current exploration and minig at this mine, as well pg. 132 as the gemological characteristics of—and cutting and setting guidelines for—Sweet Home rhodochrosite, are covered in the article by artist Kimberly Knox and Sweet Home pg. 146 Rhodo president Bryan Lees. A very soft material, rhodochrosite can still be worn in some jewelry if it is carefully set, as in this unusual necklace of rhodochrosites with enamel mounted in 18k gold. The necklace was designed by kimberly knox and manufactured by Ms. Knox and Zane A. Gillum of Golden Pacific Arts, San Diego, California. The rhodochrosites range from 1.50 to 14.06 ct. The loose rhodochrosites, which range from 6.50 ct. to 11.50 ct., are courtesy of The Collector’s Edge, Golden, Colorado. Photo © Harold & Erica Van Pelt—Photographers, Los Angels, CA. Color separations for Gems & Gemology are by pacific color, Carlsbad, CA. Printing is by cadmus journal Service, Richmond, VA. © 1997 Gemological Institute of America All rights reserved. ISSN 0016-626X Carlsbad: A new home for GIA and GEMS & GEMOLOGY About 10 years ago, a new instructor called me and asked if he could visit the Gems & Gemology offices. A great fan of the journal, he wanted to see where it was produced and meet the people responsible. I will never forget his surprise when he saw our little office and reception area, in a comfortable, but small, corner on the ground floor of GIA’s Santa Monica headquarters. “But,” he said, “from the quality of the publication, I always imagined that Gems & Gemology occupied the better part of a three-story building . .” I was delighted that he had that image of Gems & Gemology. Our goal 17 years ago, when I was asked to redesign and reformat the journal, was to use G&G as a springboard to enhance the professionalism of gemology both in the scientific community and with the trained gemologist. To this person, we had achieved that goal—too well, perhaps, because now he felt that G&G’s facilities did not reflect the role that the journal had assumed in the gemological community. It was a refrain that was being heard worldwide about GIA and its sub- sidiaries in the late 1980s. Through its education, laboratories, instruments, research, and publications, GIA had estab- lished a unique leadership position in the world gemological community. Yet, while the facilities in Santa Monica were state-of-the-art when they were first built in the 1970s, they eventually became inadequate in terms of space and future planning to meet the needs of the industry. Today, Gems & Gemology is in that three-story building—one of three buildings on the Robert Mouawad Campus. The new campus fulfills a dream and years of hard work under the guidance of GIA’s president Bill Boyajian. Beautifully designed and constructed, the Carlsbad world headquarters sits on a hill overlooking the Pacific Ocean, about 30 miles (48 km) north of San Diego and only 100 miles (160 km) south of GIA’s former home in Santa Monica. The spacious Carlsbad facility can comfortably accommodate 1,000 students and staff members. The new West Coast GIA Gem Trade Laboratory already employs more than 100 graders. The Education building has 19 classrooms and two student lounges with room for expansion. The new library and information center houses more than 20,000 publications, supported by an expanded staff. An auditorium and a gem museum are planned for the future. The new Gems & Gemology area, on the second floor of the administration building, looks out on the coastal mountains of Southern California from a wall of windows. With space for six employees and a number of visiting authors, the Gems & Gemology area is now truly a place to be proud of. Do come visit us. Share our pride. Like Gems & Gemology, GIA’s new world headquarters is dedicated to serving you and all members of the gem and jewelry community. As with all such moves, however, we have had to say good-bye to some old friends during this one. With this issue, C. W. (Chuck) Fryer, a former director of the West Coast GIA Gem Trade Laboratory, retires as editor of the Lab Notes section. Thank you, Chuck, for the years that you have devoted to making Lab Notes one of the most popular features of the journal. Alice S. Keller EDITOR Editorial GEMS & GEMOLOGY Summer 1997 79 UPDATE ON EMERALDS FROM THE SANDAWANA MINES, ZIMBABWE By J. C. (Hanco) Zwaan, Jan Kanis, and Eckehard J. Petsch Zimbabwe’s Sandawana mines have been t is believed by some that the area now known as an important producer of emeralds for 40 Zimbabwe was the fabled land of Ophir, which pro- years. Since the mines came under new duced gold for King Solomon’s temple. By the middle ownership in 1993, consistent production Iof the 10th century, the discovery of ancient gold workings has been established and, in addition to in different parts of the country had led Arab geographers to the small sizes for which Sandawana is speculate on Ophir in their writings (Summers, 1969). known, greater numbers of polished stones Although gold, and even diamonds, stimulated exploration as large as 1.50 ct have been produced. in the 20th century, for gemologists the most important dis- Currently, mining at the most active area, the Zeus mine, is done underground, with covery was the large emerald deposit found in the mid- the ore processed in a standard washing/ 1950s at the area called Sandawana. For four decades, screening trommel plant. Sandawana em- Sandawana has provided the jewelry industry with large eralds can be readily separated from em- quantities of fine, if typically small, emeralds (figure 1). eralds from other localities. They have high Production was sporadic for much of this period, but new refractive indices and specific gravities. ownership in the mid-1990s has brought renewed attention Two amphiboles, actinolite and cumming- to exploration and mining, with excellent results in terms of tonite, are abundant inclusions; albite and both the quantity and quality of the stones produced. apatite are common. Also found are rem- Although the Sandawana mines have been known for nants of fluid inclusions. Chemically, some time now, only short articles on the characteristics of Sandawana emeralds typically have a Sandawana emeralds have been published to date. There has very high chromium content. been little information about the mining area and the tech- niques used for exploration, mining, and processing. This article attempts to fill that gap. Not only does it provide some results of a detailed study on the geologic factors that contributed to emerald formation in this part of Zimbabwe, but it also offers new data on the distinctive properties of ABOUT THE AUTHORS these emeralds. Mr. Zwaan is curator at the Mineralogy Department of the National Museum of Natural HISTORICAL BACKGROUND History (NNM), Leiden, The Netherlands, and In 1868, German geologist Carl Mauch uncovered some of head of the Netherlands Gemmological Laboratory, Leiden. Dr. Kanis is a consulting geol- the ancient gold workings to which Arab geographers had ogist/gemologist specializing in gemstone occur- referred—in the interior of what is now Zimbabwe, near rences; he resides in Veitsrodt near Idar- Hartley (now Chegutu). Subsequently, after Cecil Rhodes’s Oberstein, Germany. Mr. Petsch is president of the firm Julius Petsch Jr., Idar-Oberstein. British South Africa Company obtained a charter to pro- Please see acknowledgments at end of article. mote commerce and colonization in Zimbabwe in 1889, prospecting for gold became a major industry. The simplest Gems & Gemology, Vol. 33, No. 2, pp. 80–100 © 1997 Gemological Institute of America surface indicator was an ancient working. In the nine years between 1890 and the outbreak of the South African Boer 80 Sandawana Emeralds GEMS & GEMOLOGY Summer 1997 Figure 1. The Sandawana mines are known for the small but fine emeralds that have been produced there for more than 40 years. This 16-strand necklace is composed entirely of Sandawana emeralds, more than 1,000 beads, which range from 4 to 7 mm in diam- eter. Courtesy of Fine Emerald, Inc., New York City; photo © Harold & Erica Van Pelt. War in 1899, over 100,000 gold claims were pegged in the Belingwe district (now Mberengwa) by (Summers, 1969). Laurence Contat and Cornelius Oosthuizen, two The search for gems in Zimbabwe appears to be former civil servants who had relinquished their more recent and can be dated only from H. R. posts to take up full-time prospecting. This first Moir’s 1903 diamond find in the Somabula Forest stone was recovered in the Mweza Hills about 5 km (Mennell, 1906). Some prospecting and minor min- west-southwest of the confluence of the Nuanetsi ing for diamonds took place between 1905 and (now Mwenezi) and Mutsime Rivers.

Load more

  85

Copy Link