Photoluminescence spectroscopy of Cr3+ shows considerable potential for probing local cation arrangement in MgAl2O4 spinel while undergoing order-disorder phase transition. The PL spectrum consists ...of R peaks (caused by ordered PL centers) and N peaks (caused by disordered PL centers). The peak dominating in the PL spectra dramatically switched from R peaks to N peaks around 850 °C and showed rather few changes above 900 °C. We defined the percent ratio of the integrated area of N peaks to the total integrated area under all peaks as a parameter to monitor the degree of disordering. This parameter can quantitatively indicate the variation of neighboring atom arrangement around Cr3+ during the order-disorder transition. A thermodynamic model based on this spectroscopic parameter can be built, and we can model the transition with an activation energy of 254 ± 49 kJ/mol. This study also attempted to determine the ability to restore the ordering of heated spinels by annealing them at 650 °C up to 8 days. Our results clearly indicated that the spectra cannot be fully restored back to the ordered state within our experimental time span, thus makes PL spectroscopy a reliable method to distinguish natural spinel from heated ones.
•Photoluminescence spectroscopy.•Local order-disorder transition of MgAl2O4: Cr3+.•New parameter.•Spectroscopic model.
Diaspore, is related to bauxite in terms of its formation mechanism. Diaspore is one of the gemstone quality stones used in jewelry and jewelry making. It is possible to come across gemstones in ...various regions of the world. In our country, there are gemstone deposits in all regions. In these deposits, diaspore crystals are considered very valuable. Within the scope of this study, it was aimed to determine the gemological features of the diaspore formations in Sodra (Milas-Mugla) and its surroundings, as well as to determine other minerals and their formation conditions. Main oxide, trace, and rare earth element analyses were performed on seven collected samples. The classification was made using the Al
2
O
3
-SiO
2
-Fe
2
O
3
triangular variation and it was determined that bauxite samples were in the “ferric bauxite” and “bauxite” areas. SEM imaging and EDS analyzes were performed on the samples and according to this result, it was determined that the samples mainly contained O, Al, and Si. The data obtained as a result of Raman Spectroscopy were matched with the device’s own data library and it was determined that the samples taken from the Sodra region were diaspore. In addition, according to the results of the FTIR analysis performed on the faceted sample taken from the Sodra region, it was seen that the samples were compatible with the reference standards and it was scientifically proven to be a diaspore crystal with gemstone quality. During the field studies carried out in the study area, diaspore crystals were encountered in the Milas-Sodra region, together with chloritoid and muscovite, within the metabauxite formations and in the altered zones close to the metabauxite limestone contact. Rock were classified as “muscovitequartzschist,” “quartzschist” with grano-lepidoblastic texture, “micaquartzschist” with lepidoblastic texture, “phyllite” with lepidoblastic texture, and “chlorite-epidote fels” with nematoblastic texture as a result of petrographic analyzes performed on the country rock samples. It is predicted that these gemstone-quality diaspore crystals can be evaluated economically.
Gemology is one of the mineralogical science and is facing a great challenge to identify various natural, synthetic and simulant gem materials, especially the geographic origin determination of high ...value gemstones is strongly required by gem trade and consumer. However, gemologist and research scientist in gemological laboratories must improve on their experience in identification skills, geological field studies, collecting available samples and establish an informative data base by combination of traditional gemological observations and advanced analytical instrumentations. It is very important to understand the new finding gemstone deposits and gemstone treatment procedures and development of advance sophisticated instrumentation to support the difficulties of gemological identification.
The production and trade of objects manufactured from the skeletal axis of coralid precious corals is a historically, culturally and economically important global industry. Coralids are members of ...the diverse Coralliidae family, which contains several species complexes and morphospecies. For most precious coral found in the jewelry trade, the color remains the sole clue and link to the taxonomic identity of the individual. Different coralid species have however similar or overlapping colors resulting in difficulty to taxonomically identify jewelry objects, including four species listed by the Convention on the International Trade of Endangered Species (CITES) whose international transport and trade requires species-specific and country of origin documentation. We aimed at developing a reliable method to taxonomically identify coralid material with the objective of distinguishing CITES protected species from their non-protected counterparts. We present Coral-ID, a genetic assay to taxonomically classify coralid objects using quasi non-destructive sampling. The assay classifies the analyzed sample in one of six taxonomic categories and performs at least presumptive separation of CITES-listed and non-listed species in all cases. Developmental validation experiments prove that Coral-ID is a specific, accurate and very sensitive method. As the first attempt to randomly sample corals in the trade to identify them, we applied Coral-ID on 20 precious coral objects seized by custom authorities upon import to in Switzerland. Thirteen (65%) of these samples could be analyzed; three of these were found to be presumptively CITES-listed, and 10 of them have proven to originate from non-CITES-listed species.
•A genetic assay to separate CITES listed non-CITES-listed precious coral species.•Forensically validated, highly sensitive and specific system.•A method suitable for “quasi non-destructive” samples taken from of valuable objects.•A first attempt to randomly sample corals in the trade to identify them.
The color of most garnets is derived from multiple color‐producing elements (chromophores). In this study we selectively isolate the ultraviolet–visible–near infrared (UV–Vis–NIR) spectra of four ...major chromophores (Fe2+, Mn2+, Cr3+ and V3+) by collecting and extrapolating the spectra of four representative pyrope‐almandine‐spessartine (pyralspite) garnets. In order to study the color strength of these isolated chromophores and their impact on color change in garnet, we have proposed a new quantitative definition of strength of a chromophore. With the isolated garnet chromophore spectra, hypothetical garnet spectra with various chemical compositions can be simulated. By using these hypothetical garnet spectra, the impact of each chromophore on the color change behavior in pyralspite garnet was also quantitatively studied. Most pyralspite garnets can be successfully modeled using these four chromophores, however, this model cannot adequately describe those garnets containing the Fe3+/Fe2+ intervalence charge‐transfer transitions. Finally, a comprehensive excel data processing template (Appendix 3) written with VBA macro code was generated to help other researchers calculate colorimetric parameters and color panels from UV–Vis–NIR spectrum. In the template, we provided multiple types of conversion matrices and power distribution curves of different illuminants, so that different colorimetric parameter conversion and color panel calculation from UV–Vis–NIR spectrum can be selected with different combinations based on people's preference. The user guide of the excel template can be found in Appendix 4. The detailed calculation procedures and formulae used for the excel template can be found in Appendix 5.
Figure 1. (A) The Euclidean distances between these color panels and the absolute white point (L* = 100, a* = 0, b* = 0) are all the same, which means these color panels have the same color strength. (B) Different chromophores (Mn2+ and V3+) can have different impact on the color change phenomenon in pyralspite garnets.
Turquoise is a well-known gemstone that has been used in artefacts across many cultures throughout history. However, due to its porosity it is often treated to enhance its color and beauty. One ...appreciated treatment is the patented Zachery process, although its details remain publicly undisclosed. Previous studies indicated that only a high K content distinguishes Zachery-treated from natural turquoises. In this study, natural and Zachery-treated turquoise samples from the famous Kingman mine, Arizona, USA, were analysed by means a multi-methodological approach, including standard gemological testing, electron microprobe (EMPA), scanning electron microscope with energy dispersive spectrometer (SEM–EDS) and X-ray diffraction (XRD), Fourier-Transform InfraRed (FTIR), non-destructive External Reflection-Fourier-Transform InfraRed (ER-FTIR) spectroscopy and X-ray computed microtomography (μCT). The results revealed new chemical–mineralogical and microstructural features that distinguish the Zackery-treated from the natural turquoise: higher specific gravity and lower porosity, associated with high and uneven concentrations of Cu, K and Na, the occurrence of tenorite (CuO), the presence and extension of reaction edges in the entire volume are distinctive of treated samples. Moreover, Cu-rich seeds and feldspar crystals may be interpreted as additional components used during the treatment. The hypothesis is that the Zachery treatment induces the re-crystallization of a new turquoise-like phase, which differs from the natural one from a chemical and microstructural point of view.
Gemstones are minerals of gem qualities used for adornment and decoration with the attributes of beauty, durability and rarity. Traditionally, although China has been regarded as the most important ...source for nephrite, over the past decades, a large variety of gemstone resources have been newly discovered in China owing to continuous exploration works. The vast land with various geological and geochemical backgrounds is rich in gemstone resources with potential for new deposits discoveries. In pegmatites, gemstones are related to granitic magma events and mainly occur in pegmatitic cavities, such as tourmaline, aquamarine, spodumene, spessartine, moonstone, quartz, apatite, and topaz. The eruption of Tertiary basaltic magma provides gem-quality sapphire, spinel, olivine, garnet, and zircon. The supergene oxidation zones of some copper and iron deposits in Hubei and Anhui province host gem-quality turquoise and malachite. Moreover, the formation of the nephrite deposit in China is mostly related to the carbonatite and serpentinite rocks involved in the metamorphic-metasomatic processes. This paper comprehensively introduces the distribution of gemstones deposits, as well as the gemological and mineralogical characteristics of gemstones in China. Our present investigation provides insights into the gemstone potential of China for further exploitation.
PDF
