Search Results (118)

Synthetic opal-based photonic materials with tunable optical properties not only exhibit significant application potential but also provide valuable models in terms of understanding color formation mechanisms in natural gemstones. Inspired by natural fire opals containing small amounts of Fe₂O₃ nanoparticle inclusions (0 wt%~0.23 wt%), we fabricated short-range ordered opal films doped with low concentrations (0 wt%~2.00 wt%) of Fe₂O₃@SiO₂ core–shell nanoparticles using a modified vertical deposition method. The Fe₂O₃@SiO₂ nanoparticles were synthesized via a sol–gel process to encapsulate the Fe₂O₃ core with a 10-nm-thick SiO₂ shell, preventing agglomeration and enhancing the chemical stability. Experimental results show that even small amounts of doping significantly affect the reflection peak intensity of the films, leading to notable color appearance changes. Combined with numerical simulations, we attribute this modulation to both light absorption and backward scattering effects introduced by the doped nanoparticles. Moreover, the numerical simulation results for Fe₂O₃ nanoparticles and Fe₂O₃@SiO₂ nanoparticles (with a 10 nm silica shell and similar particle size) show comparable optical properties, suggesting that such inclusions may contribute similarly to the color formation mechanisms in natural fire opals. This work demonstrates that low-concentration Fe₂O₃@SiO₂ NP doping provides an effective strategy to tune the color appearance of opal films, with implications for both structural color material development and gemological research. Full article

Borosilicate minerals of the tourmaline supergroup are valuable both for collectors and for geological research, as their chemical composition reflects the growth-medium conditions and their evolution. Tourmalines show a wide compositional variability, with pink tourmalines being particularly prized as gemstones. This study examines the crystal chemistry of pink tourmalines from Cruzeiro (Brazil), Nuristan (Afghanistan), and Malkhan (Russia) using Electron Microprobe Analysis, Micro Laser Induced Breakdown Spectroscopy (LIBS), and Single Crystal X-ray Diffraction. The results show that the pink tourmalines are Mn-rich elbaite, with the pink coloration linked to Mn at the Y site, indicating crystallization from Mn-rich pegmatitic fluids. LIBS spectra suggest a Li-rich pegmatite origin. The samples show differences: Cruzeiro exhibits strong chemical zoning, Nuristan has a uniform composition, and Malkhan shows slight zoning with high F content. A comparison with a pink tourmaline from Anjanabonoina (Madagascar) reveals that it is Ca-rich, belonging to the calcic group and crystallizing in an open system influenced by external Ca-rich fluids, contrasting with the closed system of the samples from Cruzeiro and Nuristan. The sample from Malkhan shows an anomalous chemical variation of Ca and requires further investigation. Full article

Grossular, a widely recognized colored gemstone in the market, attains premium quality when exhibiting pale-toned orange-yellow to golden-yellow hues with high transparency. Recently, our research team identified abundant gem-grade grossular associated with skarn-type polymetallic deposits in the Mt.Bozhushan area. However, these grossular specimens are currently discarded as mining waste. To promote their sustainable utilization, we conducted a systematic sampling of Mt.Bozhushan grossular and performed comprehensive analyses including fundamental gemological testing, spectroscopic characterization, and compositional profiling through EPMA and LA-ICP-MS. This multidisciplinary approach aims to establish an objective valuation framework for Mt.Bozhushan-derived grossular. The compositional and spectral data obtained in this study provide critical theoretical foundations and technical references for developing the gemstone resources of southeastern Yunnan’s Mt.Bozhushan grossular while establishing an evaluative baseline for grossular specimens from other regional deposits. Full article

This study explores the factors influencing the body color of kyanites and the chromogenic mechanism from a novel perspective of gemstone chromaticity. The gemological properties of 20 samples from Coronel Murta, Minas Gerais, Brazil, were characterized using a color spectrophotometer, Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV–Vis). The results indicate that the Fe content in kyanites significantly affects the hue angle h°, chroma C*, and colorimetric coordinate b*, with higher Fe concentrations resulting in a deeper blue hue. Additionally, the Cr and Ti contents influence the body color of kyanites. As the Ti content increases, the lightness L* of kyanites decreases. In the UV–Vis spectrum, the lightness L* of natural samples is significantly related to the wavelength corresponding to the first peak in the orange-red region, and the absorption band at 600 nm also influences the hue angle h°. Full article

The fermentation time of fermented milk significantly influences its taste and nutritional value. Monitoring the fermentation process is crucial for ensuring the quality, flavor, and safety of fermented products. In this paper, the kefir fermentation process, as an example, was monitored in situ using advanced nuclear magnetic resonance (NMR) techniques. The fermentation process was tracked by obtaining pure shift spectra through the Pure Shift Yielded by Chirp Excitation (PSYCHE) sequence to separate heavily overlapped peaks, which enabled the identification and quantification of protons. The Gradient-Enhanced, Multiplet-Selective, Targeted-Observation NMR Experiment (GEMSTONE) sequence was employed to selectively excite the protons of interest in the overlapping region, enabling the rapid tracking of changes in the lactose and ethanol concentrations during fermentation. The results from these advanced NMR methods provide valuable insights into the dynamics of the kefir fermentation process, offering a more accurate and efficient way to monitor and control the fermentation of milk. Full article

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

Gem-quality green vanadium grossular (var. tsavorite) is exclusively hosted in the Neoproterozoic Metamorphic Mozambique Belt (NMMB). The geochronology of tsavorite is limited until now, and the accurate crystallization age of the tsavorite in Kenya has remained unknown. Based on conventional gemological analyzing, by means of modern testing methods such as gemological analysis, UV-visible spectroscopy, Infrared spectroscopy, Raman spectroscopy, Electron probe, the spectral characteristics and chemical composition of tsavorite were determined, aiming to investigate the coloring elements of green garnets and trace the origin of tsavorite samples. The UV-Vis-NIR spectra and chemical composition analysis results show that vanadium and chromium are the main coloring elements in green tsavorite from Kenya. Combining the values of the δ¹⁸O (14.11‰) with the V/Cr ratio (around 4.4) of the tsavorite samples, the accuracy of the sample source has been identified. U–Pb dating of tsavorite from Kenya provides a concordant U-Pb age of 626.3 ± 4.6 Ma, in agreement with the weighted mean ²⁰⁶Pb /²³⁸U age of 625.9 ± 4.7 Ma (MSWD = 0.36), which indicated that Kenyan tsavorites were generated during the East African orogeny. Application of in situ laser U-Pb geochronology on gem-quality tsavorite to determine the mineralization time of Neoproterozoic Metamorphic Mozambique Belt of Kenya, which is the first step in characterizing the in situ dating analysis of gemstone tsavorite in Kenya mineral deposits Full article

Mica is a kind of important rock-forming mineral in the lithosphere of Earth, which can be a superior tool used to trace the origin and late evolution of rock. The Jian forsterite jade (a kind of geological skarn) is an emerging kind of gemstone in China with a beautiful color and luster, discovered in Ji’an County, Jilin Province, Northeast China. It is mainly composed of rare Mg-rich forsterite (Mg^# (Mg/(Mg + Fe²⁺) up to 99), serpentine and brucite. The source of hydrothermal fluid triggering the late metamorphism (the serpentinization of forsterite) of forsterite jade deposits remains unclear. We report a series of phlogopites with a regular range of mineral compositions in the forsterite jade deposit. Micrographs show that the phlogopites are associated with forsterite and coexist with serpentine in forsterite jade, tourmaline and tremolite in the contact zone, and plagioclase in pegmatite, and the related replacement of phlogopite seems to have not occurred. The phlogopites that occurred as single grains or veinlets in forsterite jade named type I are characterized by high X_Mg, ranging from ~0.98 to ~0.95, and the phlogopites that occurred in the contact zone of forsterite jade and pegmatite named type II are rich in Fe, with a range of X_Mg from ~0.82 to ~0.66. Additionally, the type II phlogopites are also rich in Ti, Mn, Cl, Li, Rb, Zn, V, Co, Nb and Ta but poor in Na, Sr and F compared to the type I phlogopite. Petrological and mineralogical characteristics and geochemical compositions suggest that the phlogopites are crystallized from the corresponding fluid component by hydrothermal metasomatism. The abundant Mg of the fluid phase is produced during the serpentinization of forsterite, triggered by pegmatitic hydrothermal fluid, and other main materials like K, Al, Si and H₂O are provided by the intrusive pegmatite. With the occurrence of and regular compositional variation in phlogopites in the forsterite jade deposit, we suppose that the hydrothermal fluid triggering the serpentinization of the Jian forsterite jade is produced by the intrusive pegmatite. Full article

Jade is a highly valuable and diverse gemstone, and its spectral characteristics can be used to identify its quality and type. We propose a jade ultraviolet (UV) spectrum recognition model based on deep learning, called SpectraViT, aiming to improve the accuracy and efficiency of jade identification. The algorithm combines residual modules to extract local features and transformers to capture global dependencies of jade’s UV spectrum, and finally classifying jade using fully connected layers. Experiments were conducted on a UV spectrum dataset containing four types of jade (natural diamond, cultivated diamond (CVD/HPHT), and moissanite). The results show that the algorithm can effectively identify different types of jade, achieving an accuracy of 99.24%, surpassing traditional algorithms based on Support Vector Machines (SVM) and Partial Least Squares Discriminant Analysis (PLS_DA), as well as other deep learning methods. This paper also provides a reference solution for other spectral analysis problems. Full article

The jaspers located in the Topçam Mountain, Tepeyurt region (Tokat, Turkey), were formed at green-colored metavolcanic levels within Permian–Triassic schists. The sizes of the jaspers generally vary from a few cm to 1.5 m, and their colors vary from grayish–reddish–brownish/blackish tones depending on the increase in the amount of Fe and Mn elements they contain. According to thin section and X-ray Diffraction (XRD) analysis examinations, it was determined that the composition of jaspers includes quartz, hematite, calcite, and pyrite. As stated by the Wavelength Dispersive X-ray Fluorescence (WDXRF) analysis results, it was observed that the amount of SiO₂ in jaspers was 82.5%, and the amount of Fe₂O₃ was 15.5%. According to Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analysis results, Fe and Mn impurities, which are thought to cause the color of jaspers, as well as the amount of Fe (6975.5 ppm–46,893.9 ppm–96,431.1 ppm) and the amount of Mn (935.9–3219.7–6040.4 ppm), caused a darkening in color tones (grayish–reddish–brownish/blackish). Cabochon cutting applications were made of jaspers taken from the study area. As a result of these applications, it has been determined that jaspers can be used as gemstones due to their properties, such as their workability, polish retention, and color and light reflection. Full article

This study, conducted a spectroscopic analysis of 10 gem-quality blue tourmaline samples from Minas Gerais, Brazil, focused on detailed variations in their infrared, Raman, and UV-VIS spectra. Conventional gemological tests, electron-probe microanalysis, infrared spectroscopy (mid- and near-infrared), Raman spectroscopy, and UV-visible spectroscopy were used to systematically analyze the chemical composition and spectral characteristics of the samples. The infrared spectra revealed vibrations of [YO₆], [TO₄], [BO₃], [OH], and H₂O groups, indicating different bonding profiles, with the [OH] vibrational frequency showing a direct correlation with FeO and MnO content. The Raman spectra primarily reflected the stretching vibrations of metal–oxygen bonds and hydroxyl groups, indicating the complexity of the local environment in the crystal structure. The UV-VIS spectra showed that the broad absorption band around 725 nm was due to intermetallic charge transfer between Fe²⁺ and Fe³⁺. This work provides new insights into the local bonding environment within the crystal structure by providing precise spectral data of natural blue tourmaline, and a more accurate classification and evaluation of blue tourmaline through fine spectral change characteristics related to crystal chemistry has important implications for both academic research and the gemstone industry. Full article

The aim of this study was to explore the feasibility of quantitatively evaluating a sapphire’s color by analyzing gemstone images. The color characteristics of gemstones through photography and color extraction were accurately captured, and the key color parameters for different color regions of gemstones were extracted. Then, the color of sapphires was simulated by statistical method and function simulation method. The results indicate that the brightness value of the bright area was the highest and the chroma value of the “fire” area was the highest. The chroma (C) of the sapphires was linearly positively correlated with the absolute value of its b value, and the brightness (L) showed a quadratic correlation with its chromaticity parameters (b or C). The function simulation method with an average of b as the main independent variable had a larger standard deviation, which proves that this method has a stronger ability to distinguish the differences in a sapphire’s color. This method can be extended to the color evaluation of other colored gemstones, and it can be used to form a gemstone color evaluation system. 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