In this study more than 450 natural sapphire samples (most of basaltic type) collected from 19 different areas were examined. They are from Dak Nong, Dak Lak, Quy Chau, two unknown sources from the north (Vietnam); Bo Ploi, Khao Ploi Waen (Thailand); Ban Huay Sai (Laos); Australia; Shandong (China); Andapa, Antsirabe, Nosy Be (Madagascar); Ballapana (Sri Lanka); Brazil; Russia; Colombia; Tanzania and Malawi.

gems, corundum, inclusions.5, Vietnam.12, Laos.12, Thailand.12, Australia.12, China.12, Madagascar.12, Sri Lanka, Brazil, Russia, Colombia, Tanzania, Malawi

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

Determination of gem provenance is a topic of research in the gemological community for nancial, security, and societal reasons. Laser-induced breakdown spectroscopy (LIBS) and multivariate analysis have the potential to revolutionize the eld of gem provenance. This study acquired LIBS spectra from 569 rough sapphire and ruby specimens from 21 localities in 11 countries. The spectra were analyzed using the multivariate technique partial least-squares regression (PLSR) in separate algorithms for sapphires and rubies. Each algorithm consists of a series of PLS models. Each model compares the spectra from a locality of interest to the spectra from all other localities in the database. Success rates, as determined by the percent of correct provenance identi cations, are 98.9% (sapphire) and 96.0% (ruby) for country of origin and 97.9% (sapphire) and 95.4% (ruby) for deposit of origin. Individual deposits are not recognized by the concentrations of a few elements; rather, the unique compositional signature of each deposit consists of the ratios of many elements, primarily Ca, Zr, Fe, Ba, Mt, Ti, Sr, Si, Cr, H, C, and Li, some of which may reside in inclusions. This work demonstrates that determination of country or deposit of origin may be related to a quantitative measure with a high level of success.

corundum, chemistry.2, geology.11, origin determination, gems

corundum, inclusions.5, Kenya.12, gems

Discovered during the late 1970s, the Snezhnoe ruby and sapphire deposit in Tajikistan was active until the collapse of the former Soviet Union in the early 1990s and the outbreak of regional conflicts. This marble-hosted occurrence has seen renewed interest, as it is a large and potentially productive deposit that has not been sufficiently studied. Testing of samples identified solid inclusions of margarite enriched with Na and Li (calcic ephesite or soda margarite). These are believed to be previously unreported for gem corundum. Allanite, muscovite, and fuchsite (chromium-bearing muscovite) were identified for the first time in ruby and sapphire from Snezhnoe. These and other inclusions such as zircon, rutile, K-feldspar, and Ca-Na-plagioclase could serve to distinguish them from stones mined elsewhere. Concentrations of trace elements were typical for ruby and sapphire of the same formation type. The highest Cr concentrations were observed within the bright red marble-hosted rubies, and these values were very similar to those of the famous Burmese rubies from Mogok.

corundum, geology.11, Tajikistan.12, 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.

spinel, treated spinel, cobalt diffusion, gems

Heat treatment of corundum in Sri Lanka has likely been performed on gems for near 1000 years or more as Teifaschi, an Arab writer wrote the following in 1240 (Sersen, 1991): “In Serandib (Sri Lanka) and its environs, ruby is treated by fire. People take pebbles from the earth and crush and compress them into a mass with the aid of water. (This mixture) is daubed completely around a dry stone. Then, the whole thing is placed on a rock with other rocks set down around it. Dry firewood is thrown on the top, lit and blown upon (with bellows). The blowing is applied, along with more wood, till any black overtones on the ruby have disappeared. The amount of fire and the application of wood depends on the extent of the blackness present. People know this by experience. They heat-treat stones for at least one hour and, at most, twenty days and nights. Then, they carefully extract the ruby, its blackness having disappeared.” This description can be applied to the “blow pipe technique” we still can witness today in Sri Lanka (see Figure 1.) This technique is used is to remove or partially remove some blue components in rubies and sapphires to give in the case of rubies the appearance of a purer hue. In the past it was also used to turn light blue sapphires colorless. Another particularly interesting description of that treatment is also given by James Emerson Tennent, an English traveler who wrote “Ceylon an account of the Island” in 1859: “The blue tinge which detracts from the value of the pure ruby, whose colour should resemble “pigeon’s blood,” is removed by the Singhalese, by exposing the stone in the lime of a calcined shell and exposing it to high heat.” This reference is to the best knowledge of the authors also one of the earliest mention of “Pigeon’s Blood” in the English literature. A similar type of heat treatment of ruby to the ‘blow-pipe’ technique is also practiced in Vietnam and Thailand where a simple jeweler’s torch is used for few seconds or minutes and this is sometimes referred to as “snake bite” (see Figure 3 left). Usually only inclusion free stones are heated this way as included stones are likely to be damaged by the process. Generally the stone does not need to be repolished after this “snake bite” treatment.

corundum, treatments.6, Mozambique.12, gems

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, corundum, inclusions.5

A diamond is so much more than merely a cov- eted mineral specimen or gemstone. Whether a natural crystal or transformed into a glittering gem by the lapidary’s hand, diamond is a unique messenger bearing extraordinary tales from Earth’s depths. To the unaided eye, euhedral crystals (fig. 1) and flawless, colorless faceted diamonds may offer a message too subtle to register, while a more tortured, less aesthetic specimen may be dismissed entirely. However, with the aid of the microscope, a surface landscape of surprisingly detailed features is revealed, and its interior becomes a veritable world-within-a-world, ripe with important insights and intriguing mysteries begging to be investigated.

gems, diamond, inclusions

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.

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

In April 2014, one of the authors (VP) was preparing a field expedition to visit sapphire deposits in Nigeria. During the preparations he contacted several West African gem merchants in Bangkok to arrange to see some samples and seek additional details about the sapphire deposits in Nigeria. This interest was fueled by the emergence of Nigeria as an important producer of gemstones over the past few years, and the lack of publications on the sapphires and sapphire deposits from and within the country. During one of these discussions he was shown a parcel of blue sapphires reportedly from a new deposit located on the Mambilla Plateau (Taraba State) in Nigeria (Figure 1). Over the following weeks, more parcels containing stones of similar appearance showed-up in Thailand, and also in Sri Lanka, as many Sri Lankan gem merchants reportedly rushed to Nigeria. All the people we met were very excited by the quality and the size of the stones being produced. Large clean stones were reported, some weighing between 100 and 300 carats with a nice blue color. Reports emerged that stones from the new deposit were being traded at very high prices. One stone reportedly sold for more than 1 million US dollars in Thailand. Photos of such stones rapidly started to appear on social media sites (Figure 2) and were also frequently encountered on the mobile phones of some West African gem merchants visiting Thailand.

corundum, inclusions.5, geology.11, Nigeria.12, 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.

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

Sapphire-bearing dikes are located in the Little Belt Mountains, Montana. This report gives an accurate and comprehensive review of the sapphire deposit and its history. Yogo sapphires constitute a world-class deposit hosted by an ultramafic ouachitite (lamprophyre) dike system of Eocene age (about 50 million years old) in central Montana. The sapphires are mostly cornflower-blue, have extremely few inclusions, and are not zoned. With high brilliance and luster in both natural and artificial light, they do not require heat treatment to enhance their color. It is estimated that since discovery in 1895 production is 18.2 million carats of rough gems with 500,000 carats of faceted sapphires. Most of the gems are less than 1 carat, platy, and relatively thin, although specimens up to 19 carats have been reported. The largest sapphire with a suitable thickness for faceting as a single gem was 12.25 carats.

gems, corundum, USA.12, Montana.12, Yogo Gulch

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

Mineralogical and gemmological properties of synthetic alexandrites grown by the horizontally oriented crystallization (HOC) method are described. The method is used to grow crystal plates weighing up to 450 g. The morphology of the rough crystals is dependent on the form of the molybdenum boat used as a container for crystal growth. The most significant inclusions for gem identification are curved growth striations and flat, irregularly- shaped somewhat elongated cavities. Microprobe analyses revealed distinct amounts of chromium and vanadium but extremely low iron contents. Spectra in the UV-Vis range are consistent with published work. Six differently sized cubes were cut from an HOC alexandrite crystal and used to show pleochroism in combination with two optical phenomena: the alexandrite effect and the Usambara effect. Colorimetric parameters were calculated from the spectra of the cubes and plotted in the CIELAB colour space to demonstrate the alexandrite and Usambara effects graphically for different directions of view. The absorption bands in the infrared are polarized and assigned to structural OH-groups.

gems, synthetic chrysoberyl, Russia, horizontally oriented crystallization

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

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

In the last five years, fine Burmese blue sapphires from the Baw Mar area of Mogok have reached the market. The faceted stones typically show a strong pleochroism from greenish to violetish blue when viewed perpendicular and parallel to the c-axis, respectively, with medium to strong saturation and medium to dark tone. Most of the samples were relatively clean under the microscope, showing multiple twinning with whitish needle-like inclusions (presumably boehmite) at the intersections. Often, these in-clusions were associated with stress tension fissures. Needles, most likely rutile, were found only occa-sionally, but small platelets and needle-like particles, probably ilmenite, appeared more frequently. Most of the stones contained surface-reaching open and healed fissures, but crystal inclusions of K-feldspar and mica (identified by Raman) were occasionally encountered. The sapphires also had a relatively high iron content, low gallium, and very low titanium. Their Ga/Mg ratio varied from 0.6 to 17. Their UV-Vis-NIR spectra displayed intense iron-related absorptions, and the FTIR absorption spectra presented mainly boehmite-and mica-related bands. Based on careful microscopic observations, combined with spectro-scopic and chemical analysis, the sapphire from Baw Mar can, in most cases, be distinguished from the blue sapphire of other localities.

corundum, Burma.12, gems

Rubies from Montepuez in northern Mozambique are particularly interesting as this new material rapidly dominated the ruby trade in Thailand, the world’s major ruby trading center, since the discovery of the deposit during the spring of 2009. This new material is quite different from rubies traditionally encountered in the market such as the marble type rubies, known for their strong fluorescent aspect related to their low iron content, like those from Mogok or Mong Hsu in Myanmar (Burma) or basalt related rubies, known for their low fluorescence due to higher iron content, from Thailand or Cambodia. Indeed the new deposit in Montepuez is not marble or basalt related but instead is an amphibole related deposit similar to the ruby deposits near Winza (Tanzania), M’Sawize (Mozambique) and probably the deposit near Didy (Madagascar), three other ruby deposits discovered fairly recently in Africa. Amphibole type rubies usually have higher iron content than those commonly found in marble related deposits but also usually exhibit lower iron content compared to those from basalt related deposits. It is interesting to note that these non-classic (i.e. amphibole type) metamorphic stones fill the gap, in relation to chemistry and appearance, between the highly fluorescent marble type rubies and the weakly fluorescent basalt related rubies familiar to the trade. For gemologists willing to find out where the gems they are studying come from, the fact that the rubies from Montepuez are coming from an amphibole related deposit is fascinating as the combination of the inclusion scene, the chemical fingerprint and the spectra associated with these stones will usually enable them to differentiate these gems quite easily from their cousins mined from marble or basalt related deposits. The data presented here, using GIA reference samples, should be very helpful in this regard.

corundum, inclusions.5, geology.11, Mozambique.12, gems

For centuries the Mogok metamorphic belt of Myanmar (a.k.a. Burma) has been famous for producing classic, pigeons-blood ruby (corundum: Al2O3) specimens. The present model for the formation of rubies hosted in marble from the Himalayan arc is a closed-system metamorphism of former clays from evaporitic/organic-rich shale units in margin basins. Mogok has still not been fully included in this model. Involvement of igneous intrusions and the formation of skarn with the marble has been an outstanding topic. Twenty-three red corundum samples (nominally rubies) from eight sources in the Mogok belt marbles, including a skarn setting and local alluvial samples, have been analyzed using the electron microprobe and a laser ablation-inductively coupled plasma-mass spectrometer system to measure trace element compositions for evidence of different geological formational environments. Although inclusions, such as baddeleyite (ZrO2) and srilankite ([Ti,Zr]O2), as well as associated painite (CaZrAl9O15[BO3]), indicate skarn-related paragenesis of some samples, no signatures of B or Zr enrichment were found. Rather high levels of Si (300+ ppm) are found, possibly indicating nano-silicate inclusions when above 500 ppm. A distinct Fe enrichment, as in the case of metasomatic ruby, is observed. Sensitivity to the sub-ppm level may to be necessary to resolve, if even possible, whether there is a compositional signature from the skarn formation. Samples from individual sources in the belt show some distinct trace-element characteristics, in particular a discretely limited variation in V/Ti while the Cr content can vary considerably and independently. With the potential of V, Ti, and Cr being sourced from blackshale components in shelf carbonates that were transformed to marble, these Mogok belt rubies may record an informative intersection of organic chemistry, geochemistry, plate tectonics, metamorphism, and metasomatic processing.

corundum, geology.11, Burma.12, gems

corundum, inclusions.5, treatments.7, gems