Search Results (9)

The trapiche garnet, a gemstone of unparalleled beauty, boasts a rare structure comprising one core, six radiating arms, and a main body. The occurrence of garnet within the trapiche structure elevates it beyond the species, granting it significant scientific and gemological value. In this study, we conducted the first systematic investigation of trapiche garnets from the Chun’an area, Zhejiang Province, China. These samples were proven grossular through the analysis of spectroscopy and major elements. The trace element features are consistent with the distribution patterns of garnet in hydrothermal metasomatic skarn. Microscopic observation and Raman spectroscopy revealed that dark inclusions within the core and arms consist predominantly of amorphous carbon. The in situ U-Pb dating of the trapiche garnets revealed a crystallization age of 120.7 ± 4.7 Ma, corresponding to the late Yanshanian movement. It is speculated that the contact metasomatism between magma enriched in Al and surrounding rock led to the formation of calcareous skarn. This study provides insights into gemological, geochemical, and chronological characteristics, broadening the research on trapiche structures, and enhancing the understanding of gemstone mineralization timing and local tectonic activity. Full article

The initial nucleus of gemstones at the Natural History Museum of the University of Florence (Italy) is linked to the significant collection of the Medici family, who began it as early as the 15th century. The present research aims to study this collection in order to (1) comprehensively review the archival and catalogue information available; (2) identify the mineralogical species correctly; and (3) gather information on the potential provenance of the gem deposits. To address these objectives, fifty gems were investigated using entirely non-invasive methods, ensuring the preservation of the collection’s precious and historical value. All specimens underwent autoptic observation and micro-Raman analysis, while a selection was further examined using PIXE-PIGE to characterise their chemical composition, including trace elements. The gems were attributed to seven mineral species: emerald, topaz, grossular, cordierite, quartz, orthoclase, and tourmaline. One gem was identified as a fake, made of glass and likely produced in the 17th century. Twenty-nine of the historical attributions in the catalogue were found to be incorrect and were subsequently revised. In some cases, the trace elements and mineral inclusions identified in the gems enabled the determination of potential provenance deposits, which were then compared with the available archival information. Full article

The characterization of objects of historical and cultural interest represents a crucial topic, specifically when it regards gemstones. Actually, the advanced investigation of precious minerals of gemological interest requires exclusively non-destructive analyses which are also suitable for determining their provenance when it is unknown. In this study, a non-destructive analytical protocol, previously tested on diamonds for petrogenetic studies, has been applied to a natural diamond of very high historical and gemological value, donated in 1852 by Monsignor Lavinio de ‘Medici Spada to the Museum of Earth Sciences of Sapienza University (Rome). The analytical protocol used includes X-ray diffraction topography, micro-computed X-ray tomography, single-crystal micro-X-ray diffraction and Fourier-transform infrared spectroscopy. The results show the presence of dislocations originating from inclusions and a very low degree of plastic deformation. The aggregation states of its N impurities show that this diamond is type IaAB, while the inclusions consist of olivine (Fo92-93), suggesting a lithospheric origin. The historical references found in the catalogs of the Museum indicate only a Brazilian origin, without any reference to the mining district. The information acquired in this study, enhanced by document research on mining in Brazil since 1700, suggests that the diamond likely comes from the district of Diamantina, Mina Gerais, Brazil. Full article

The Malysheva emerald mine (Urals, Russia) boasts a long history and extraordinary emerald output. However, recent studies indicate that Malysheva emeralds share highly similar inclusion varieties, UV-visible-near infrared (UV-Vis-NIR) spectra, and compositional characteristics with other tectonic-magmatic-related (type I) emeralds from Zambia, Brazil, and Ethiopia. This similarity poses challenges for determination of the emeralds’ origin. This paper systematically investigates the microscopy, spectroscopy, and trace element chemistry of Malysheva emerald samples and compiles previously reported compositional data for the aforementioned Type I emeralds. Based on this dataset, principal component analysis (PCA) and machine learning methods are employed to construct models for emerald provenance discrimination. The results have updated the provenance characteristics of Malysheva emeralds, confirming the solid phase component of their three-phase inclusions as siderite and revealing two UV-Vis-NIR spectral patterns. Furthermore, the unique infrared absorptions related to HDO and D₂O molecules within the 2600–2830 cm⁻¹ range were discovered, which can be indicative of the origin of Malysheva. The prediction results of the machine learning model demonstrate an accuracy rate of 98.7%, and for an independent validation set of Malysheva emeralds, the prediction accuracy reached 100%. The feature importance ranking of the model highlights trace elements and parameters strongly correlated with the emeralds’ origin. These results illustrate the enormous potential of machine learning in the field of emerald origin determination, offering new insights into the traceability of precious gemstones. Full article

In the last century, a blue–green colored gemstone known as Larimar with a special sea-wave pattern was discovered in the Dominican Republic. Larimar is composed of the mineral pectolite, which has a chemical composition of NaCa₂Si₃O₈(OH) and is usually white in color. Cu²⁺ has always been considered to be the primary genesis of the blue color shown in Larimar, because native copper often grows together with Larimar. To clarify whether copper is the main reason for the origin of blue–green pectolite, we utilized laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) techniques to analyze trace elements in the pectolite samples and compared the relationship between elements and colors. The results show that vanadium and iron are the main origins of the sky-blue and green color of Larimar. We also discovered that it is not only the chemical elements that affect the color shades of the mineral, but the orientation of the radial fiber crystals also plays a critical role. The sea-wave pattern and the changes in the color saturation of radial pectolite are due to the transmittance of visible light through different viewed angles under changing crystal orientations. Our results reveal the chemical and physical factors behind the color and sea-wave pattern of Larimar. In addition, to our knowledge, this is the first time that the formation age of Larimar has been proven to be approximately equal to or younger than 40 ka, using the U-Th dating of calcite growth together with pectolite. Full article

The Jizerka Quaternary alluvial placer in the Czech Republic has been a well-known source of gemstones since the 16th century, and the only one in Europe that has yielded a significant amount of jewel-quality sapphire. Besides Mg-rich ilmenite (“iserine”), which is the most common heavy mineral at the locality, some other minerals have been mined for jewellery purposes. These are corundum (sapphire and ruby varieties), zircon (“hyacinth” gemstone variety) and spinel. Here, we present a detailed petrological and geochronological investigation of the enigmatic relationship between the sapphires and their supposed host rocks, supporting their xenogenetic link. Our hypothesis is based on thermal resetting of the U–Pb isotopic age of the zircon inclusion found inside Jizerka blue sapphire to the estimated time of the anticipated host alkaline basalt intrusion. The host rocks of the gemstones (sapphire and zircon) and Mg-rich ilmenite are not yet known, but could be related to the Cenozoic volcanism located near the Jizerka gem placer (Bukovec diatreme volcano, Pytlácká jáma Pit diatreme and Hruškovy skály basalt pipe). The transport of sapphire, zircon and Mg-rich ilmenite to the surface was connected with serial volcanic events, likely the fast ascent of alkali basalts and formation of multi-explosive diatreme maar structures with later deposition of volcanoclastic material in eluvial and alluvial sediments in nearby areas. All mineral xenocrysts usually show traces of magmatic corrosion textures, indicating disequilibrium with the transporting alkali basalt magma. In order to constrain the provenance and age of the Jizerka placer heavy mineral assemblage, zircon inclusion and associated phases (niobian rutile, baddeleyite and silicate melts) in the blue sapphire have been studied using LA–ICP–MS (laser ablation–inductively coupled plasma–mass spectrometry) geochemistry and U–Pb in situ dating. Modification of the zircon inclusion into baddeleyite by exposure to temperature above 1400 °C in a basaltic melt is accompanied by zircon U–Pb age resetting. A zircon inclusion in a Jizerka sapphire was dated at 31.2 ± 0.4 Ma, and its baddeleyite rim at 31 ± 16 Ma. The composition of the melt inclusions in sapphire and incorporated niobian rutile suggests that the parental rock of the sapphire was alkali syenite. The Eocene to late Miocene (Messinian) ages of Jizerka zircon are new findings within the Eger Graben structure, as well as among the other sapphire–zircon occurrences within the European Variscides. Jizerka blue sapphire mineral inclusions indicate a provenience of this gemstone mineral assemblage from different parental rocks of unknown age and unknown levels of the upper crust or lithospheric mantle. Full article

Currently, most of the popular spinels in the jewellery market come from Myanmar and Tajikistan. It is well known that provenance is one of the main factors affecting the value of a gemstone, and the geographic origin of a gemstone can be determined by examining its gemological and inclusion characteristics. This study systematically characterized the conventional gemology of spinels from Myanmar and Tajikistan and compared the inclusions in the spinels from these two countries by means of gemological microscopy and Raman spectroscopy. The results showed that most red and pink Myanmarese spinels were octahedral or contact twins, while Tajikistani spinels are slabbed or octahedral distorted crystals. Columnar zircon is frequently found in Tajikistani spinels but rare in Myanmarese spinels, appearing as tiny accessory inclusions. There are three types of carbonate inclusions (magnesite, dolomite, and calcite) in Myanmarese spinels, but Tajikistani spinels have only one (magnesite). In addition, spinels of different origins include special inclusions. Myanmarese spinels contain pyrite inclusions; Tajikistani spinels contain rutile and talc inclusions. Full article

Raman and photoluminescence (PL) mapping is a non-destructive method which allows gemologists and scientists to evaluate the spatial distributions of defects within a gem; it can also provide a method to quickly distinguish different species within a composite gem. This article provides a summary of this relatively new technology and its instrumentation. Additionally, we provide a compilation of new data for various applications on several gemstones. Spatial differences within diamonds can be explored using PL mapping, such as radiation stains observed on the rough surface of natural green diamonds. Raman mapping has proven useful in distinguishing between omphacite and jadeite within a composite of these two minerals, identifying various tourmaline species within a heterogeneous mixture, and determining the calcium carbonate polymorphs in pearls. Additionally, it has potential to be useful for country-of-origin determination in blue sapphires and micro-inclusion analysis. As new avenues of research are explored, more applications for gem materials will inevitably be discovered. Full article

The Chiaravalle Cross, a masterpiece of Mediaeval goldsmithery, went under restoration in 2016. This was a unique opportunity to undertake an in-depth multidisciplinary study. Several issues were addressed, as for example the chronology of the Cross, lacking any official document about it. The scientific investigations included in situ and laboratory measurements, and the analyses, part of a multidisciplinary protocol, completely characterized the gemstones adorning the Cross, the cameos, the gold, silver, jasper and glass parts, to derive indications on their provenance, authenticity and dating issues. All the results were shared with the whole collaboration of experts, which included art historians, a restorer, a conservator, a scholar in ancient glyptic, gemologists, archaeometallurgists, physicists and scientists in a very fruitful exchange of knowledge. This work is an example of a real multidisciplinary research, gathering good practices in the study of a complex piece of art. Full article