gems, jade, jadeite, fei cui, Japan

This paper presents a review of Itoigawa’s jadeitite in history, culture, process of rediscovery, and geological characteristics. The people of the Jomon age used jadeitite as tools as far as 7000 years ago, making it one of the oldest jadeitite cultures in the world. The jadeitites from Itoigawa were the source of ornaments such as pendants or comma–shaped beads that can be dated to the Jomon age through to the Nara period. These ornaments are widely found in Japanese Islands from Hokkaido to Okinawa Prefecture, and also in the southern part of the Korean Peninsula. The jadeitite, however, was not used after the Nara period. The disappearance of jadeitite culture is not well understood, but it may have been caused by the introduction of Buddhism into Japan. Therefore, the existence of jadeitite in Japan was forgotten for a period of 1200 years after the Nara period. Mr. Eizo Ito rediscovered jadeitite from Itoigawa when he identified the durable green rock in the Kotakigawa River in 1938. His success was inspired by the idea of Mr. Gyofu Soma. The rediscovered jadeitite was studied by Dr. Yoshinori Kawano of the Tohoku Imperial University in 1939. There are large jadeitite boulders weighing more than 100 tons found in several areas of the Kotakigawa and Ohmigawa Rivers. These areas are designated national natural monuments. The jadeitite from Itoigawa can be found in various colors such as white, gray, black, lavender, and blue. These color variations are caused by the presence of trace elements such as iron and titanium in jadeite and omphacite, and tiny graphite inclusions in jadeitite. The absence of quartz and euhederal jadeite crystals with natrolite and veinlets of jadeitite indicates that the Itoigawa jadeitite does not form through decomposition of albite, but by hydrothermal activity. Some strontium dominant minerals such as itoigawaite were first found in jadeitite from Itoigawa. These strontium dominant minerals form in the calcium depleted hydrothermal solution in the late stages of jadeitite formation. The Jomon is the oldest jadeitite culture worldwide, and the first documented use of precious stones in the history of mankind. In addition, the jadeitite found in Itoigawa is the oldest known unit of its kind.

gems, beryl, emerald, Afghanistan, Brazil, Colombia, Zambia, Madagascar, China, Pakistan, Zimbabwe, inclusions

The French chemist N.L. Vauquelin (1763–1829) discovered chromium (Cr) in crocoite (PbCrO₄) from Beresov, Russia, and beryllium (Be) in emerald from Colombia more than 200 years ago. He determined the correct chemical composition of emerald and demonstrated that the difference between beryl and emerald was due to the presence of the coloring agent chromium. Today, emerald is defined by Schwarz and Schmetzer (2002) as “yellowish green, green or bluish green beryl—natural or synthetic—which reveals distinct Cr and/or vanadium (V) absorption bands in the red and blue-violet ranges of its absorption spectra.” Emerald is one of the most valuable gemstones. It is much rarer than diamond and can command a value thousands of times greater than gold. In the colored gemstone market, color is more important than clarity or brilliance in determining the value of an emerald. The green color of emerald arises from the unique geological conditions of its formation in contrasting environments. This article reviews, using state-of-the-art data, the crystal chemistry and formation of emerald, highlighting its paradoxes, as well as the geology of economically significant emerald deposits worldwide, comparing their origins, similarities, and differences.

corundum, Montana.12, Missouri River, USA.12, sapphire, Rock Creek, gems, inclusions.5

Although the source rocks of alluvial sapphires in Montana have never been discovered, inclusions and geochemistry of material from this location may give clues to their original source. Mineral inclusions in alluvial Montana sapphires, mainly from Rock Creek, were identified and compared with existing data. Topaz was a remarkable find in one of these samples; other newly identified mineral inclusions in Montana sapphire were allanite, anatase, chalcopyrite, and monazite. Together with the presence of calcium-rich plagioclase, alkali-feldspar, apatite, barite, phlogopite, a pyrochlore-group mineral previously called uranpyrochlore, and chromite/spinel, these inclusions may reflect a metasomatic origin for the sapphires. This is supported by their chemical composition, which largely coincides with sapphires of plumasitic/metasomatic origin. The secondary Montana sapphires analyzed in this study are characterized by mean values of Fe (4686 ppmw), Ti (58 ppmw), Ga (51 ppmw), Mg (35 ppmw), and Cr (21 ppmw). Fe-Mg-Ga ratios help to distinguish them from sapphires with overlapping properties, such as those from Umba, Tanzania, and Rio Mayo, Colombia.

corundum, inclusions.5, Kenya.12, gems

spinel, treated spinel, cobalt diffusion, gems

Recently (May 2015) several unusual looking faceted spinels were submitted to GIA’s New York, Carlsbad, and Bangkok identification laboratories. At the same time and within the social media it was announced by GRS Laboratory that Mr. M.T.M Harris of Emteem Gem Laboratory had reported seeing similar stones coming through his laboratory in Beruwela, Sri Lanka, and that GRS in cooperation with Günther and Harris (Peretti 2012 (updated 2015)) had determined that the stones were diffused with cobalt. From their inclusion scenes these stones appeared to have been heated at high temperatures, in particular this seemed to be so from the dissolved state of numerous solid inclusions and a profusion of fractures that seemed to have been artificially healed in a flux environment. Cobalt along with iron is known to contribute to the observed color of natural blue spinels from a number of locations (Harder 1986, Chauviré 2015, D'Ippolito 2015) however those colored mostly by cobalt have become sort after both in the general trade as well as with collectors. As such it is important that a clear distinction between natural cobalt spinels and those that owe their color to the artificial addition of cobalt be made and the techniques needed for this distinction be available for all to use. The following text, images and data set out the detail and results of the authors’ examination of eighteen samples supplied to them by the individual responsible for devising the process and placing the material in the market -Mr. Thamrong Charasaiya, who is the President of T.N., High Tech Gems limited, located in Ladprao, Bangkok Thailand. Mr. Charasaiya informed the authors’ that his treatment involved the “deep diffusion cobalt” into “low colored natural spinel from Burma” resulting in a strong blue color. He further stated that “cobalt will not diffuse into spinel on its own and that iron had also to be present along with the cobalt for the process to work”. The authors greatly appreciate the assistance of Mr. Charasaiya in donating the specimens for this examination as well as the open discussions that have taken place that have provided further useful information on the process being used. However it should be emphasized at the outset that the details of his process remain proprietary to Mr. Charasaiya and any description of it here results from the conversations we have had with him -the authors have not witnessed the actual treatment taking place and nor do they have details on such important areas as the manner in which the diffusion materials are applied, the temperatures or timescales used.

gems, corundum, inclusions.5

Until recently, film was the preferred medium used for capturing images through the microscope, pri-marily due to resolution limitations of digital-format cameras. The image quality that can now be achieved by digital cameras is equal, and in many ways superior, to the quality offered by film. Digital photomicrography allows gemologists the opportunity to instantly see the resultant images, which can then be adjusted with image-refining software so that they represent their subject as realistically as pos-sible. This article offers examples of some basic techniques and tips on the application of digital pro-cessing to get the most out of photomicrographs.

gems, beryl, emerald, Colombia, Muzo, Chivor, Cosquez, Zambia, Afghanistan, Panjshir

Until now, the observation of three-phase inclusions in emeralds has been considered a potential indicator of Colombian origin. Nevertheless, emeralds from Afghanistan (Panjshir Valley), China (Davdar), and Zambia (Kafubu and a new deposit at Musakashi) may contain three-phase inclusions resembling those often found in specimens from Colombian deposits (Muzo, Chivor, La Pita, Coscuez, and Peñas Blancas). This article presents detailed photomicrographs of samples from these localities, with a focus on their multiphase inclusions. Also investigated are spectroscopic features and trace-element data. For the gemologist studying the origin of emeralds hosting three-phase inclusions, a powerful set of tools to aid in this determination comes from the combination of detailed microscopic examination, UV-VisNIR and FTIR spectroscopy, and LA-ICP-MS trace-element analysis.

corundum, ruby, sapphire, Madagascar.12, Placer in alkali-basalt, Gem corundum deposits, Chemical composition, Oxygen isotopes, Genetic model, gems

Madagascar is a major producer of gem corundum, primarily recovered from continental basaltic fields. Key mining areas include sapphire-bearing palaeoplacer deposits such as Ambondromifehy and Nosy Be in Antsiranana Province (northern Madagascar), Soamiakatra–Mandrosohasina in Antananarivo Province (central Madagascar), and the Vatomandry district in Toamasina Province (eastern Madagascar). In Antananarivo Province, Soamiakatra is a primary deposit where rubies occur in metagabbro and pyroxenite xenoliths transported to the surface by the Ankaratra volcanic activity. Petrographic evidence indicates two distinct ruby-forming conditions: near the eclogite domain (T ≈ 1100 °C, P ≈ 20 kb) and in granulite facies (T ≈ 1100 °C, P < 15 kb). In contrast, sapphires from placer and paleoplacer deposits mainly originate from two sources: (i) magmatic sapphires (90%) derived from alkaline magma differentiation in lower crust–mantle boundary chambers, associated with syenite and anorthoclasite xenoliths in alkali-basalts. These are linked to asthenospheric upwelling and lithospheric thinning during Oligocene–Quaternary times. Zircons from Mandrosohasina and Ambatomainty sapphire deposits yield U–Pb ages of 7 Ma. These sapphires have low δ¹⁸O values (4.1 ± 0.4‰, n = 8), matching those from syenitic sources. Inclusions such as columbite-(Fe), tantalite-(Mn), pyrochlore group minerals, samarskite group minerals, uraninite, and anorthoclase further confirm syenitic origins. (ii) The remaining 10% are metamorphic xenocrysts brought up by the same magmatic event. Rubies from placer deposits show δ¹⁸O values of 3.1 ± 1.1‰ (n = 6), consistent with ruby in mafic–ultramafic rocks and metasomatic ‘plumasite’ zones (δ¹⁸O = 1.25–7.5‰, n = 35). In Toamasina Province, ~85% of the sapphires from Vatomandry are metamorphic, with δ¹⁸O = 4.1 ± 0.4‰ (n = 9), overlapping the range for metasomatic sapphires from ‘plumasites’ and biotite schists in shear zones. The remaining ~15% are magmatic, with low δ¹⁸O values consistent with sapphire-bearing syenites. In Antsiranana Province, rubies are absent; sapphires are ~40% magmatic and ~60% metamorphic, with δ¹⁸O = 4.5 ± 0.5‰ (n = 11), comparable to the other provinces. Zircons yield contrasting U–Pb ages: 40.6 Ma (Ambondromifehy) and 0.7 Ma (Nosy Be). These data—corundum characteristics, isotopic signatures, and radiometric ages—demonstrate two distinct corundum sources in Madagascar’s alkali-basalts. One comprises rubies from metagabbro and garnet–pyroxenite complexes of eclogite facies, retrograded to granulite facies during the Pan-African orogeny. The other includes sapphires either magmatic, coeval with volcanic events involving differentiated alkaline magma, or metamorphic, extracted from Precambrian basement during magma ascent.

gems, glyptic, engraved gems, agate, cameo, intaglio, Getty Museum, locality, species, analytical, garnet

The results of quantitative electron microprobe analyses, along with observations of gemmological properties and microscopic features, are presented for 11 garnets of ancient Greek, Etruscan, and Roman origin. In addition to chemical data, the gemmological properties of the Getty Museum garnets are examined, including refractive index, density, and inclusions. Based on their chemical composition and gemmological properties, the 11 garnets are categorized into four groups: Cr-poor pyrope, Mn-rich almandine, Ca-rich almandine, and intermediate pyrope-almandine. When combined with published analyses of 26 Greek and Roman garnets from ancient jewelry and glyptics, the chemical distribution pattern of all 37 garnets expanded the boundaries of the established groups, introducing a fifth group consisting of Mn-poor almandine. The compositional fields for these five groups are compared with data from Early Medieval garnets, mostly from Merovingian cloisonné jewelry. The chemical composition and physical properties of the garnets provide insights into potential sources of rough gem material, trade and transmission networks in the ancient world, and associations between finished objects now dispersed across different collections.

gems, corundum, India.12, Kashmir, sapphire, inclusions.5

Brief note about Kashmir sapphires, with two new inclusion finds (spinel and hematite)