Search Results (141)

The Sar-e-Sang lapis lazuli deposit has a mining history exceeding 5000 years, producing the world’s finest lapis lazuli. Recently, gem-quality forsterite has been discovered in the marble containing spinel, dolomite, and phlogopite at the periphery of the lapis lazuli ore body at the Pitawak mine, located east of the Sar-e-Sang deposit. The mineral assemblage indicates that the protolith of this marble is dolomite with aluminous and siliceous components. These forsterite crystals occur as colorless, transparent anhedral grains, exhibiting distinct red fluorescence under 365 nm ultraviolet light. To investigate the gemological and spectroscopic characteristics of the Pitawak mine forsterite, this study conducted and analyzed data from basic gemological analysis, electron probe microanalysis (EPMA), Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), ultraviolet–visible absorption spectroscopy (UV-VIS), Fourier-transform infrared spectroscopy (FTIR), laser Raman spectroscopy (RAMAN), and photoluminescence spectroscopy (PL) on four forsterite samples from the Pitawak mine. The analysis results reveal that the samples indicate a composition close to ideal forsterite with a crystal chemical formula of (Mg_2.00Fe_0.02)_Σ2.02Si_0.99O₄. The trace elements present include Fe, Mn, Ca, and minor amounts of Cr and Ni. The UV-VIS spectroscopy results show that the samples possess high transmittance across the visible light range with very weak absorption bands, contributing to the colorless and transparent appearance of Pitawak mine forsterite. This phenomenon is attributed to the extremely low content of chromophoric elements, which have a negligible effect on the forsterite’s color. PL spectroscopy indicates that the red fluorescence of the samples is caused by an emission peak near 642 nm. This emission peak arises from the spin-forbidden ⁴T₁ → ⁶A₁ transition of Mn²⁺ ions situated in octahedral sites within the forsterite structure. Full article

Yuanjiang County is one of the most important gem-producing areas in China. The authors of this study discovered and collected gem-quality andradite Garnsts in the epidote amphibolite from the periphery of the ruby deposit in Shaku Village, Yuanjiang County. After careful observation of the collected andradite, it was found that these andradite samples appear green when the thickness is less than 2 mm and reddish-brown when the thickness is greater than 2 mm, exhibiting the typical Usambara effect. To investigate the gemological and spectroscopic characteristics of Yuanjiang andradite, this study conducted basic gemological tests, microscopic observation, electron probe microanalysis (EPMA), ultraviolet–visible (UV-Vis) absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and laser Raman spectroscopy on the collected samples. Tests show that Yuanjiang andradite has a lower specific gravity than typical andradite, which is due to the presence of epidote inclusions inside. EPMA results indicate that the samples contain a certain amount of Cr element. The crystal chemical formula of the samples calculated from the EPMA results is (Ca_2.89–2.93, Mn_0.01–0.02, Fe_0.15–0.10)(Fe_1.69–1.95, Al_0.00–0.23, Cr_0.00–0.23, Si_0.05–0.08)(SiO₄)₃. UV-Vis tests show that the samples have transmission windows in both the green- and red-light regions, with Fe³⁺ and Cr³⁺ acting as the main chromogenic ions, among which Cr³⁺ is crucial for the occurrence of the Usambara effect. The FTIR and Raman test results are basically the same as previous research results, but some peak positions related to metal cations differ from the theoretical values, which may be caused by the presence of a certain amount of Cr³⁺ in the samples. Full article

Africa hosts numerous emerald deposits, among which Sumbawanga, located at the junction of Tanzania, Zambia, Congo, and Malawi, stands out as one of the significant localities. This study presents a comprehensive analysis of the gemological, spectroscopic, and inclusion characteristics of Sumbawanga (Tanzania) emerald samples utilizing techniques such as gem microscopy, UV-Vis-NIR spectroscopy, Raman spectroscopy, GEM-3000, and EPMA, etc. These emerald crystals look like rolled pebbles and display a bluish-green coloration. They contain fingerprint-like fluid inclusions, which occasionally encompass a circular bubble (the gas phase is CO₂). Sumbawanga emeralds are characterized by abundant mineral inclusions, including quartz, apatite, anhydrite, diaspore, chrysoberyl, rutile, hematite, and magnetite. Particularly diagnostic are the mineral inclusion of chrysoberyl twins and the assemblages of quartz and diaspore. Full article

Maw-sit-sit jade resembles kosmochlor-jadeitite in appearance and is spatially associated with it in the Myanmar Jade Belt. However, the mineral composition, microstructure, and petrogenesis of this type of jade remain unclear. To address this gap, this study investigated high-quality Maw-sit-sit jade using a range of analytical techniques, including conventional gemological tests, infrared spectroscopy, petrographic observations, electron probe microanalysis (EPMA), and backscattered electron (BSE) imaging. Results show that Maw-sit-sit jade primarily consists of albite and chromium-omphacite, with minor amphibole (eckermannite and richterite). Jadeite and relict chromite are absent in the studied samples. Its high albite content gives it lower refractive index (RI: 1.55–1.56) and specific gravity (SG: 2.69–2.73) compared to kosmochlor-jadeitite and jadeite jade. Additionally, Maw-sit-sit jade exhibits punctate or banded fluorescence under ultraviolet (UV) light, distinguishing it from kosmochlor-jadeitite and jadeite jade (both inert). Petrographically, euhedral albite fills interstices between early-formed Cr-omphacite and eckermannite, which is textural evidence of its late-stage origin. Eckermannite and Cr-omphacite occur as enclosed grains with embayed boundaries and dissolution pores, indicating they experienced mechanical disruption and chemical dissolution during subsequent geological processes. Petrogenetically, Maw-sit-sit jade (defined as “Cr-omphacite-albitite”) forms via a two-stage process: (1) Under high-pressure/low-temperature (HP/LT) conditions in the subduction zone, Na-Al-Si-rich fluids metasomatize chromite-bearing serpentinite protoliths, generating an early assemblage of jadeite, Cr-omphacite and amphiboles; (2) During subsequent plate exhumation and decompression, jadeite underwent retrograde metamorphism under low-pressure/low-temperature (LP/LT) conditions involving residual Na-Al-Si fluids, resulting in the formation of albite. This process led to the replacement of early-formed minerals by euhedral albite, ultimately generating the Ab+Cr-Omp+Eck symplectic texture. This study elucidates the mineralogical, gemological identity and petrogenesis of high-quality Maw-sit-sit jade, advancing our understanding of fluid evolution within a subduction zone. Full article

A recently discovered turquoise deposit in the Fangshankou area of Dunhuang, Gansu Province, has been relatively understudied compared to turquoise from other sources due to its short mining history. Currently, no relevant research literature on this deposit has been identified. Therefore, a systematic mineralogical and spectroscopic study of Dunhuang turquoise samples was conducted using conventional gemological testing methods, combined with techniques such as X-ray powder diffraction (XRD), electron probe microanalysis (EPMA), Fourier transform infrared spectroscopy (FTIR), laser Raman spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), and X-ray fluorescence (XRF) mapping. The test results indicate that the turquoise samples from this area have a density ranging from 2.40 to 2.77 g/cm³ and a refractive index between 1.59 and 1.65. The samples generally exhibit a cryptocrystalline structure, with some displaying spherulitic radial and radial fibrous structures. The texture is relatively dense and hard, with particle diameters less than 10 μm. Chemically, the turquoise samples from this region are characterized by high Fe and Si content and relatively low Cu content. Samples contain, in addition to the turquoise mineral, other minerals such as quartz, goethite and alunite, etc. The oxide content ranges are as follows: w(P₂O₅) between 23.83% and 33.66%, w(Al₂O₃) between 26.47% and 33.36%, w(CuO) between 5.26% and 7.91%, w(FeO) between 2.46% and 4.11%, and w(SiO₂) between 0.97% and 10.75%. In the infrared absorption spectra of Dunhuang turquoise, the bands at 3510 cm⁻¹ and 3464 cm⁻¹ are attributed to ν(OH)⁻ stretching vibrations, while the bands near 3308 cm⁻¹ and 3098 cm⁻¹ are assigned to ν(M-H₂O) stretching vibrations. The infrared absorption bands near 1110 cm⁻¹ and 1058 cm⁻¹ are due to v[PO₄]³⁻ stretching vibrations, and the bands near 651 cm⁻¹, 575 cm⁻¹, and 485 cm⁻¹ are attributed to δ[PO₄]³⁻ bending vibrations. A clear correlation exists between the Raman spectral features and the infrared spectra of this turquoise. The hue and chroma of the turquoise from this area are primarily influenced by the mass fractions of Fe³⁺, Cu²⁺, and Fe²⁺, as well as their bonding modes with water molecules. The ultraviolet-visible spectra are attributed to O²⁻–Fe³⁺ charge transfer, the ⁶A₁–⁴E_g + ⁴A₁ transition of Fe³⁺ ions (D⁵ configuration) in hydrated iron ions [Fe(H₂O)₆]³⁺, and the spin-allowed ²E_g–²T_2g transition of Cu²⁺ ions in hydrated copper ions [Cu(H₂O)₄]²⁺. Associated minerals include goethite, alunite, jarosite, and quartz. Fine-grained quartz often exists as secondary micron-sized independent mineral phases, which have a certain impact on the quality of the turquoise. Full article

The Jingbaoer Grassland Jade Mine situated approximately 20 km northwest of Mazongshan Town in Gansu Province, China, represents an important source of nephrite dating back to the pre-Qin period. In this study, 58 representative nephrite samples were analyzed to investigate their mineralogical and geochemical characteristics using polarized light microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The mine is situated near the contact zone between the Silurian Gongpoquan Group and Devonian granite, with surrounding rocks primarily consisting of Precambrian dolomitic marble. The nephrite displays diverse colors—white, bluish-white, sugar-white, and cyan—with darker tones and abundant manganese-stained dendritic and flocculent inclusions. It shows a relative density of 2.82–2.99, a refractive index of 1.60–1.62, and a vitreous to greasy luster. Texturally, the jade is predominantly composed of micro-fibrous interwoven tremolite, occasionally exhibiting oriented recrystallization textures. Minor minerals include diopside, apatite, titanite, chlorite, epidote, allanite, rutile, and graphite. Chemically, the samples are rich in SiO₂, MgO, and CaO, with trace amounts of FeO, MnO, Al₂O₃, and Na₂O. Notably, Sr and Sm are enriched, Nb is slightly depleted, and Eu shows a distinct negative anomaly. The average total rare earth content is 4.25 µg/g. The study suggests that the deposits in the research area are typical of the contact-metasomatic type, formed through multi-stage hydrothermal metasomatism between acidic granitic intrusions and dolomitic marble, creating favorable conditions for the formation of high-quality tremolite jade. Comparative analysis with jade artifacts excavated from the Tomb of Marquis Yi of Zeng suggests a possible provenance link to the Jingbaoer deposit, providing valuable evidence for the historical mining and distribution of nephrite during the Warring States period. Full article

Gemstone samples, as objects of study in gemology, carry rich geological information and cultural value, playing an irreplaceable role in teaching, research, and public science communication. In the current age of big data, machine learning and artificial intelligence techniques based on gemstone databases have emerged as a cutting-edge area of gemology. However, traditional gemstone databases have three major limitations: an absence of standardized data schemas, incomplete core datasets (e.g., records of synthetic and treated gemstones and inclusion characteristics), and poor data interoperability. These deficiencies hinder the application of advanced technologies, such as machine learning (ML) and AI techniques. This paper reviews gemstone data and applications, as well as existing gem-related sample databases, and proposes a framework for a new gemstone database based on standardization (FAIR principles), integration (blockchain technology), and dynamism (real-time updates). This framework could transform the gemstone industry, shifting it from “experience-driven” to “data-driven” practices. Powered by big data technology, this novel database will revolutionize gemological research, jewelry authentication, market transactions, and educational outreach, fostering innovation in academic research and practical applications. Full article

The newly discovered multi-colored corundum (gem quality) alluvial deposit in Malipo, Yunnan Province, is one of the most famous sapphire deposits in China. However, the coloration mechanism and genesis of red-blue colored corundum (RBCC) remain enigmatic. In this study, conventional gemological techniques such as ultraviolet–visible (UV-vis) spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were employed on an RBCC suite, with a view to unravel its coloration mechanism and compositional characteristics. The results show that the element pairs of Cr³⁺, Fe²⁺-Ti⁴⁺, and Fe³⁺-Fe³⁺ in principle contribute to the red coloration, while the blue color in corundum is predominantly caused by the Fe²⁺-Ti⁴⁺ pair, and subordinately by Cr³⁺ and Fe³⁺. Cr is likely the cause of the purple color. The Cr content in the red zone is significantly higher than that in the blue zone, while the Ti and V contents in the red zone are notably lower than in the blue zone. High Cr/Ga and (V + Cr)/Ga values of the Malipo RBCC suggest a metamorphic origin. All color zones of RBCC demonstrate stability in Ga content and an extremely low content of Mg, with minor fluctuations in Fe content, indicating that the formation process of the Malipo RBCC was influenced by magma mixing. Full article

Diamond traceability has been a major challenge for the gemological industry in recent decades. In this context, this paper presents new studies using UV-VIS-NIR spectroscopy to identify the traceability and geographical origin of diamonds. The aim of the work is to identify characteristic centers of fancy-color diamonds collected from Cullinan Mine, Democratic Republic of Congo (DRC), and the geographical regions with unknown origin. Depending on the origin of the diamonds, the UV-VIS-NIR spectra can be differentiated as follows: (i) the diamonds collected from Cullinan Mine show absorption bands assigned to N₁⁰, NV⁰, NV⁻, N₃V⁰, N₄V₂, and N₄V centers, which are accompanied by a vibronic structure localized between 415 and 394 nm (2.987–3.147 eV) and (ii) the diamonds from DRC show absorption bands attributed to N₁⁰, NV⁻, N₃V⁰, N₁⁺, and NVH centers. Using Raman spectroscopy, nitrogen concentration values of diamonds collected from the Cullinan mines and DRC between 41 and 185 ppm and 204–336 ppm, respectively, were reported. We prove that the simultaneous applicability of UV-VIS-NIR spectroscopy and Raman scattering as comparative tools for assessing diamond provenance can be a valuable strategy for an initial attribution of diamonds with unknown geographical origin, knowing the optical features of diamonds collected from Cullinan Mine and DRC. Full article

Zibai Jade is a recently identified hydrogrossular-dominant jade originating from Shaanxi Province, China. It constitutes a polymineralic aggregate composed predominantly of hydrogrossular, with minor proportions of vesuvianite, diopside, chlorite, uvarovite, and calcite. A multi-method analytical approach was employed to characterize this jade, incorporating conventional gemological testing, polarizing microscopy, SEM, XRD, BSE, XRF, and EPMA, as well as UV-Vis and infrared (IR). These techniques enabled a detailed examination of its mineralogy, surface features, and color origin. The stone displays a heterogeneous color distribution, featuring a base hue of light green to yellowish-green, accompanied by distinct occurrences of emerald-green spots, dark green spots, mossy green inclusions, white patches, white veinlets, and a black dot with a green ring. Microanalytical results indicate that the emerald-green spots are principally composed of uvarovite; the dark green spots are dominated by hydrogrossular, diopside, and chlorite; fibrous green inclusions consist mainly of chlorite and Cr-bearing grossular; white patches and veinlets are primarily composed of calcite; and the black dot with a green ring predominantly comprises chromite and uvarovite. Coloration is attributed to the combined influence of Fe and Cr³⁺. The formation of Zibai Jade involved three mineralization stages: deposition of a carbonate protolith, high-temperature metasomatism, and retrograde alteration. The metasomatism was driven by hydrothermal fluids derived from granodioritic and ultramafic rocks, which provided Si, Al, and the essential Cr, respectively. The interplay of these processes resulted in the development of Zibai Jade, which exhibits a dense texture and attractive coloration. Full article

This study investigates the mechanism behind the heat-induced color change (brown to yellowish green) in Mn- and Fe-rich elbaite tourmaline under reducing atmosphere at 500 °C. A combination of analytical techniques including gemological characterization, electron microprobe analysis (EMPA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and ultraviolet–visible (UV-Vis) spectroscopy was employed. Chemical analysis confirmed the samples as intermediate members of the elbaite–fluorelbaite series, with an average formula of ^X(Na₀.₆₆ □₀.₂₆ Ca₀.₀₈) _Σ1.₀₀^Y(Li₁.₂₉Al₁.₁₀Mn₀.₃₁ Fe²⁺₀.₁₅Ti₀.₀₁Zn₀.₀₁) _Σ2.₈₇ ^ZAl₆^T[Si₆O₁₈] (BO₃)₃^V(OH)₃.₀₀^W(OH₀.₅₁F₀.₄₉) _Σ1.₀₀, enriched in Mn (17,346–20,669 μg/g) and Fe (8396–10,750 μg/g). Heat treatment enhanced transparency and induced strong pleochroism (yellowish green parallel c-axis, brown perpendicular c-axis). UV-Vis spectroscopy identified the brown color origin in the parallel c-axis direction: absorption bands at 730 nm (Fe²⁺ d–d transition, ⁵T_2g → ⁵E_g), 540 nm (Fe²⁺→Fe³⁺ intervalence charge transfer, IVCT), and 415 nm (Fe²⁺→Ti⁴⁺ IVCT + possible Mn²⁺ contribution). Post-treatment, the 540 nm band vanished, creating a green transmission window and causing the color shift parallel the c-axis. The spectra perpendicular to the c-axis remained largely unchanged. The disappearance of the 540 nm band, attributed to the reduction of Fe³⁺ to Fe²⁺ eliminating the Fe²⁺–Fe³⁺ pair interaction required for IVCT, is the primary color change mechanism. The parallel c-axis section of the samples shows brown and yellow-green dichroism after heat treatment. A decrease in the IR intensity at 4170 cm⁻¹ indicates a reduced Fe³⁺ concentration. The weakening or disappearance of the 4721 cm⁻¹ absorption band of the infrared spectrum and the near-infrared 976 nm absorption band of the ultraviolet–visible spectrum provides diagnostic indicators for identifying heat treatment in similar brown elbaite–fluorelbaite. Full article

Freshwater bead-cultured pearls (FWBCPs) from Zhuji, China, have gained significant market prominence due to their large size, unique pearl luster, and diverse color. This study systematically investigated the mineral compositions and organic color-related compounds of twelve representative freshwater cultured pearls through a multi-analytical approach integrating Fourier transform infrared spectroscopy (FTIR), Laser Raman spectroscopy (LRS), ultraviolet–visible spectroscopy (UV-Vis), cathodoluminescence (CL), micro-infrared spectroscopy, and differential thermal–thermogravimetric analysis (TGA-DTA). Key findings reveal that FWBCPs from Zhuji primarily consist of aragonite, organic matter and adsorbed water, occasionally containing vaterite. No obvious correlation was observed between the mineral compositions and the quality of the pearls. Raman spectra exhibit characteristic bands of polyenes near 1525 cm⁻¹ (attributed to the stretching vibration of C=C, ν₁) and near 1131 cm⁻¹ (attributed to the stretching vibration of C-C, ν₂). The different colors are formed by various polyenes with the exact position of the characteristic bands determined by the concentrations of C=C in the polyenes. FWBCPs and freshwater non-bead-cultured pearls (FWNBCPs) exhibit essentially the same mineral compositions and organic color-related compounds, but can be distinguished from each other based on their internal structures. These results advance the understanding of freshwater pearl formation mechanisms and establish a scientific foundation for quality evaluation in the gemological industry. Full article

This study quantitatively analyses how light sources, polishing methods, and backgrounds affect the color of “Tang yu”. Twenty-four samples were tested with three different light sources (D50, A, D65), two polishing methods, and nine Munsell neutral gray backgrounds. Testing 24 samples revealed that main coloring elements exhibit low concentrations with no linear relationship to color intensity. Light sources selectively alter chromaticity: D65 maintains color balance (recommended for grading), while A enhances red tones. Polishing methods significantly impact color perception, with glassy polishing markedly increasing Lightness (L*↑11.41%) and Chroma (C*↑42.11%) while shifting hues toward red-yellow. Background luminance (γ_b) critically influences color results: Lightness L* and Chroma C* increase via distinct power functions as γ_b rises, though Hue angle (h°) remains stable. Sample color can be predicted through γ_b based equations, with Munsell N9 background proving optimal for grading. Cluster and discriminant analyses effectively classified colors into three distinct groups, establishing a foundation for a reliable grading system. Full article

The Nujiang region of Yunnan is by far the richest tourmaline-producing mining area in China. Since the discovery of the tourmaline-bearing deposit in Yunnan Province in 1980, there have been few comprehensive gemmological studies of this deposit. Therefore, the results of tests on 32 tourmaline samples from the Fugong and Gongshan regions of Yunnan are reported in this paper. The chemical composition of the Yunnan tourmalines was analyzed, and the contents of major trace elements were compared with those of tourmaline samples from different localities reported in the literature to highlight their specific provenance characteristics. Microscopic observation revealed the presence of liquid, gas, and solid inclusions; Raman spectra indicated the presence of constitutional water and CH₄-C₂H₆ dihydrate in the Yunnan tourmalines and also pointed to the influence pattern of the Fe content. The infrared spectrum in the range of 4000–4800 cm⁻¹ showed the frequency of metal cations and hydroxyl groups. Based on the characteristic peaks at 4343 cm⁻¹ and 4600 cm⁻¹, a quick distinction between elbaite and dravite could be made. UV–Vis absorption spectroscopy analysis showed that in yellow tourmalines, Mn²⁺-Ti⁴⁺ IVCT is the main cause of color, while green coloration occurs due to Fe²⁺–Fe³⁺ interactions or Cr³⁺ and V³⁺, and the pink color is caused by Mn³⁺ d-d transitions. The three-dimensional fluorescence spectra revealed the presence of the main fluorescence peaks at λex280/λem320 nm and λex265/λem510 nm in the tourmaline samples analyzed and the fluorescence intensity with Ti and Fe contents. Full article

A new type of vesuvianite jade has recently been discovered in Hanzhong City, Shaanxi Province, China. However, a systematic investigation into its mineralogical characteristics and the origin of its color is currently lacking. In this study, the gemological, mineralogical, and spectroscopic properties of the Hanzhong vesuvianite jade were comprehensively analyzed using a suite of modern analytical techniques, including standard gemological testing, polarizing microscopy, X-ray powder diffraction, Fourier-transform infrared spectroscopy, laser Raman spectroscopy, UV-visible absorption spectroscopy, and X-ray fluorescence spectroscopy. The origin of the jade’s color was also preliminarily investigated. The results indicate that the samples are primarily composed of vesuvianite, with associated minerals including minor amounts of grossular, chlorite, and diopside, and trace amounts of calcite, epidote, chromite, and titanite. The pale green patches consist mainly of chlorite and grossular, the dark green bands are predominantly chlorite, and the dark brown patches are composed of abundant, disseminated microcrystalline chromite intermixed with uvarovite (calcium chromium garnet). The major chemical components of the vesuvianite jade matrix are SiO₂, Al₂O₃, and CaO. Specifically, SiO₂ ranges from 37.01 to 38.54 wt.%, Al₂O₃ from 18.48 to 22.84 wt.%, and CaO from 37.16 to 40.04 wt.%. Minor amounts include MgO (0.76–4.39 wt.%) and FeO_T (total iron expressed as FeO, 0.56–2.09 wt.%). The yellowish-green color of the matrix originates from a combination of ligand-to-metal charge transfer of Fe³⁺, crystal field transitions of Fe³⁺, and intervalence charge transfer between Fe²⁺ and Fe³⁺ in vesuvianite. The emerald-green color of the patches results from the synergistic effect of Fe and Cr; Fe provides a yellowish-green background color, upon which the crystal field transitions of Cr³⁺ (indicated by a doublet at 686/696 nm) impose strong absorption in the red region, resulting in a more vivid green hue. Full article