Gems & Gemology最新文献

{"title":"A Review of Analytical Methods Used in Geographic Origin Determination of Gemstones","authors":"L. Groat, G. Giuliani, J. Stone‐Sundberg, Ziyin Sun, Nathan D. Renfro, Aaron C. Palke","doi":"10.5741/gems.55.4.512","DOIUrl":"https://doi.org/10.5741/gems.55.4.512","url":null,"abstract":"GEMS & GEMOLOGY WINTER 2019 In gemology, “origin” refers to the geographic locality of a gemstone deposit (Hänni, 1994). Origin determination of colored gemstones began with Gübelin and SSEF (both in Switzerland) in the 1950s and with AGL (New York) in 1977 (Schwarz, 2015). Origin determination is of increasing importance in today’s market, and for many gems this information is considered either a value-adding factor or a positive for the salability of a gemstone (Hainschwang and Notari, 2015). Origin determination is often possible because there is a close relationship between the environment of crystallization, especially the mineralogical and chemical composition of the host rock, and the properties of the gemstones that can be studied in the lab, often using sophisticated equipment (Hänni, 1994). In this paper we review the analytical techniques (figure 1) commonly used to characterize gem materials, with a specific focus on geographic origin determination. We also review the physical and chemical properties of corundum and emerald, which have the greatest demand for origin determination. Finally, we provide examples of origin determination of corundum and emerald from the literature to illustrate how these analytical methods are applied to the problem of establishing origin.","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2019-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47695273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geographic Origin Determination of Emerald","authors":"Sudarat Saeseaw, Nathan D. Renfro, Aaron C. Palke, Ziyin Sun, S. McClure","doi":"10.5741/gems.55.4.614","DOIUrl":"https://doi.org/10.5741/gems.55.4.614","url":null,"abstract":"GEMS & GEMOLOGY WINTER 2019 When the Spanish conquistadors first brought Colombian emeralds (figures 1 and 2) onto the international market, they became a global sensation in their day. Emeralds from Central Asia and Egypt were known at the time, but the world had likely never seen emeralds of such high quality and size. Traders soon developed distribution channels that brought the Colombian material all the way from the royal courts in Europe to the powerful Moguls of India (Giuliani et al., 2000). The nineteenth and twentieth centuries saw all of this change as new mines sprang up around the world to challenge the famed Colombian emeralds. Most notable in terms of high-quality production were Brazil, Russia, and Zambia, but smaller deposits have been uncovered in Madagascar and Ethiopia and elsewhere. As the market has evolved alongside these developments, geographic origin has come to be an important factor for fine-quality emeralds. The demand for emerald origin determination was initially driven by the proliferation of sources. However, this expansion and diversification of emerald sources has also complicated origin determination. As the number of sources grows, so does the overlap in their characteristics. The following sections will detail the specific criteria used in the laboratory at GIA to make geographic origin conclusions for emeralds, as well as potential areas of overlap and how these are dealt with.","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2019-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45730154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geographic Origin Determination of Paraiba Tourmaline","authors":"Yusuke Katsurada, Ziyin Sun, C. Breeding, B. Dutrow","doi":"10.5741/gems.55.4.648","DOIUrl":"https://doi.org/10.5741/gems.55.4.648","url":null,"abstract":"GEMS & GEMOLOGY WINTER 2019 Copper-bearing gem tourmaline—recognizable by its vivid neon blue to green color—has been one of the most popular colored gemstones on the market for the nearly three decades since its debut (figures 1 and 2). It was first discovered in the state of Paraíba in northeastern Brazil in the late 1980s, and subsequently found in the neighboring state of Rio Grande do Norte (Fritsch et al., 1990; Shigley et al., 2001; Furuya, 2007). These gems became known as Paraíba tourmalines after the locality of their discovery. In the early twenty-first century, similarly colored gem-quality tourmalines were discovered in Nigeria and Mozambique (figures 3 and 4; Smith et al., 2001; Abduriyim and Kitawaki, 2005). In the gem market, Brazilian Paraíba tourmalines are typically more highly valued than their African counterparts. While top-quality Brazilian Paraíba tourmalines tend to have more intense color, there is significant overlap in the color range for all localities. Additionally, standard gemological tests cannot definitively separate stones from these three localities. As a result, there is market demand for gemological laboratories to offer origin determination for copper-bearing tourmalines. The most recent Laboratory Manual Harmonisation Committee (LMHC) definition of “Paraíba” tourmaline is “a blue (electric blue, neon blue, violet blue), bluish green to greenish blue, green (or yellowish green) tourmaline, of medium-light to high saturation and tone (relative to this variety of tour-","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2019-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42513242","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geographic Origin Determination of Alexandrite","authors":"Ziyin Sun, Aaron C. Palke, J. Muyal, Dino G. DeGhionno, S. McClure","doi":"10.5741/gems.55.4.660","DOIUrl":"https://doi.org/10.5741/gems.55.4.660","url":null,"abstract":"GEMS & GEMOLOGY WINTER 2019 A fter the discovery of a gem mineral with unusual color-change behavior in the Russian Ural Mountains during the early 1830s, Swedish mineralogist Nils Adolf Erik Nordenskiöld named this new gem alexandrite in 1834 in honor of the future Czar Alexander II (Kozlov, 2005). This immediately created a royal and romantic aura around this variety of chrysoberyl. The most coveted alexandrites exhibit a lush green to greenish blue color in daylight and a warm, bright red shade in candlelight (Levine, 2008); some fine Brazilian and Indian alexandrite examples are shown in figures 1–3 and 6. This phenomenal color change is caused by the presence of trace Cr3+ substituting for Al3+ in the chrysoberyl crystal structure. Alexandrite is routinely described as “emerald by day, ruby by night.” It is a stone of duality—green or red, cool or warm, day or night (Levine, 2008). Because of its rare and attractive color-change phenomenon, alexandrite has been highly sought after and is one of the most valuable gemstones in the trade. Alexandrite, particularly fine-quality material, is also very scarce; it has generally been a byproduct of mining other major colored stones. Overall production statistics are hard to evaluate. It has been mined in Russia (Kozlov, 2005; Schmetzer, 2010), Tanzania","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2019-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45669714","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Gemological Characteristics of Pipi Pearls Reportedly from Pinctada Maculata","authors":"Nanthaporn Nilpetploy, Kwanreun Lawanwong, Promlikit Kessrapong","doi":"10.5741/GEMS.54.4.418","DOIUrl":"https://doi.org/10.5741/GEMS.54.4.418","url":null,"abstract":"“tiny” and is used to refer to the small, predominantly yellow or “golden” pearls that originate from the bivalve mollusk Pinctada maculata (Gould, 1846). As the smallest mollusk species in the Pinctada genus, Pinctada maculata rarely exceeds 5 cm when measured in the anterioposterior or dorsoventral positions. The mollusk lives in the Indo-Pacific Ocean, mostly around French Polynesia and the Cook Islands, where they are often found in association with the Pinctada margaritifera mollusk species (Strack, 2006). Pearls from Pinctada maculata often form in round to near-round shapes. As the name implies, the small shells produce small pearls that rarely exceed 8 mm in diameter (Krzemnicki, 2014). Based on GIA’s experience, 6 mm or under is more typical of the species. Pipi pearls are known to occur as natural pearls rather than cultured and, compared with other Pinctada species, are deemed rare. One report recorded only one gem-quality pearl found from a total of 355 mollusks (Passfield, 1997). In 1950, several cultured pearl experiments using Pinctada maculata reportedly took place but were unsuccessful (Segura et al., 2014). In the late 1990s, a few Pinctada maculata cultured blister pearls resulted from experiments in the waters off Penrhyn, an island in the northern atoll of the Cook Islands (Kessrapong et al., 2017). The nacre covering the bead nuclei did not fully overgrow the nuclei, however, and this attempt was not very successful. Some reports suggest that the Pinctada maculata mollusk is not abundant enough for","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2019-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43134569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An Early Byzantine Engraved Almandine from the Garibpet Deposit, Telengana State, India: Evidence for Garnet Trade Along the Ancient Maritime Silk Road","authors":"H. Gilg, K. Schmetzer, U. Schüssler","doi":"10.5741/GEMS.54.2.149","DOIUrl":"https://doi.org/10.5741/GEMS.54.2.149","url":null,"abstract":"","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":"322 ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2018-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41276368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Black Diamonds from Marange (Zimbabwe): A Result of Natural Irradiation and Graphite Inclusions","authors":"Karen V. Smith, Elina Myagkaya, S. Persaud, Wuyi Wang","doi":"10.5741/gems.54.2.132","DOIUrl":"https://doi.org/10.5741/gems.54.2.132","url":null,"abstract":"have either natural or treated color origin. Natural black diamonds are usually colored by inclusions of sulfides, graphite, magnetite, hematite, or iron-bearing inclusions (e.g., Titkov et al., 2003). A rare natural diamond (of undisclosed geographic origin) colored by abundant brown radiation stains has previously been examined by GIA’s Carlsbad laboratory (Ardon, 2013). Treated black diamonds are often those that are heavily fractured naturally and then treated at low-pressure and hightemperature (LPHT) conditions to graphitize the fractures and turn them black (Hall and Moses, 2001; Notari, 2002). Artificial irradiation can also produce dark colors that appear black (Collins, 1982; Kitawaki, 2007). The Marange locality in eastern Zimbabwe is well known for producing diamonds that contain both octahedral and cuboid sectors (mixed-habit diamonds) where the cuboid sectors are visible to the eye due to abundant micro-inclusions of graphite (Rakovan et al., 2014; Smit et al., 2016). These micro-inclusions, informally known in the gem trade as “clouds,” give the diamonds a brown-gray appearance that lowers their value. Heat treatment of these lower-quality graphitecontaining Marange diamonds has the potential to introduce gem-quality treated black diamonds into the market. In natural diamonds, these graphite micro-inclusions are around 1 μm in diameter; during heating above 1200°C, they become larger. After annealing at 1700°C, the grain size increases to 11–16 μm, causing the cuboid sectors to appear opaque black (Eaton-Magaña et al., 2017). The challenge for gem laboratories is to confidently distinguish these treated black diamonds from naturally occurring black diamonds. Here our goal was to document a suite of untreated Marange diamonds, all with Fancy Dark brown to Fancy black GIA color grades, so that their characteristics could be distinguished from any suspected treated black diamonds. When viewing the samples, however, it became clear that the appearance of the these dark Marange diamonds was due not only to graphite clouds but also to abundant graphite needles and dark brown radiation stains occurring within surface-reaching fractures. BLACK DIAMONDS FROM MARANGE (ZIMBABWE): A RESULT OF NATURAL IRRADIATION AND GRAPHITE INCLUSIONS","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2018-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44324623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gemological Characterization of Sapphires from Yogo Gulch, Montana","authors":"Nathan D. Renfro, Aaron C. Palke, R. Berg","doi":"10.5741/GEMS.54.2.184","DOIUrl":"https://doi.org/10.5741/GEMS.54.2.184","url":null,"abstract":"Gulch, Montana, have produced millions of carats of rough sapphire. Much of that has yielded very small finished stones, and faceted stones over 1 ct are highly prized (figure 1). The largest known Yogo sapphire crystal was found in 1910 and weighed 19 ct (Howard, 1962a) The shape of Yogo rough is often in the form of flat tabular crystals that offer a very low yield. Large stones over 1 ct are almost exclusively collector stones, with the provenance having a significant impact on value. While there are other significant sources of gem-quality sapphire in Montana—including Rock Creek, Missouri River, and Dry Cottonwood Creek—Yogo sapphires are unique among these and other sapphire deposits worldwide (figure 2). Virtually all of the material produced has a desirable even blue to violet or purple color, often with higher clarity than sapphires from other deposits (Yaras, 1969) (figure 3). Yogo sapphires do not require heat treatment, offering a virtual guarantee of their untreated nature. They also possess a unique trace-element chemistry and an inclusion suite that makes them easily recognizable to the experienced gemologist. HISTORY In 1895, the Yogo sapphire deposit was accidentally discovered by a gold prospector named Jake Hoover. Hoover sought financial backing from two friends— local banker S.S. Hobson and Dr. Jim Bouvet, a veterinarian from Chicago—and the three formed a mining partnership. While recovering gold from his","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2018-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41499561","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Natural-Color Blue, Gray, and Violet Diamonds: Allure of the Deep","authors":"S. eaton-magaña, C. Breeding, J. Shigley","doi":"10.5741/gems.54.2.112","DOIUrl":"https://doi.org/10.5741/gems.54.2.112","url":null,"abstract":"","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2018-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47741425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Natural-Color Green Diamonds: A Beautiful Conundrum","authors":"C. Breeding, S. eaton-magaña, J. Shigley","doi":"10.5741/GEMS.54.1.2","DOIUrl":"https://doi.org/10.5741/GEMS.54.1.2","url":null,"abstract":"valued of gemstones due to their beauty and rarity. Interestingly, the rarest of diamond colors correlate with the three most popular choices for favorite color, in general—green, blue, and pink to red. The unique set of conditions in nature that produce the structural imperfections (defects in the lattice of carbon atoms; see Shigley and Breeding, 2013) responsible for the most vibrant hues of green, blue, and pink/red diamonds are so uncommon that many people are not even aware these stones exist. Over the last ten years, diamonds with these natural color components comprised less than 0.4% of all diamonds submitted to GIA’s laboratories worldwide (including both fancy-color and those on the D–Z scale). Pure hues of green, blue, or red are even rarer, accounting for less than 0.07% of all diamonds examined. Many articles published over the last 20 years in the scientific and gemological literature have looked at specific properties of colored diamonds, quality grading characteristics, or particular treatments. Few researchers, however, have had the opportunity to examine large quantities of similarly colored natural diamonds and report on their distinctive characteristics. Colored diamonds are extremely rare and, consequently, highly valued. This value factor means that laboratory reports are requested for most colored dia-","PeriodicalId":12600,"journal":{"name":"Gems & Gemology","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2018-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43796387","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}