http://www.gia.edu/gems-gemology/fall-2015-colombian-trapiche-emeralds-recent-advances-understanding-formationInternational audienceColombia is the traditional source of the world’s finest emeralds, including the famed trapiche crystals, with their distinctive texture resembling a wheel with six spokes. This gemological curiosity, found exclusively in the black shales of the country’s western emerald zone, is linked to the peculiar structural geology of the deposits. The study presents a review and update on Colombian trapiche emeralds, followed by a three-dimensional examination of the crystals combined with spectroscopic and chemical analyses. The proposed formation model incorporates the structural geology of the deposits with the formation of trapiche and non-trapiche emeralds. The fluid accumulation at the faults’ tip in the black shales leads to maximum fluid overpressure and sudden decompression and formation of the emerald-bearing vein system. The authors show that trapiche emerald growth starts at the beginning of the decompression that is responsible for local supersaturation of the fluid. The hydrothermal fluid comes in contact with the black shale matrix, favoring the formation of emerald seed crystals. During the growth of these seeds, textural sector zoning occurs, sometimes associated with chemical sector zoning, along with displacement of the matrix. Displacement growth occurs because the emeralds continue their growth, pushing the matrix material away from the growing faces. An overgrowth, generally of gem quality, can form after decompression, surrounding the core, the arms, and the dendrites, restoring the emeralds’ euhedral habit
Diamond BZ270 derives from within a 30 km radius of the small Rio São Luiz, near the town of Juina. The sampling site for diamond JUc4 can be more precisely constrained to 261000 m E and 8708000 m N in WGS84 UTM-projected Zone 21S (Agrosi et al. 2017; Figure DR1). METHODS Micro-Computed X-ray Tomography Micro-Computed X-ray Tomography (Cnudde and Boone, 2013) was carried out using a Scyscan 1172 microtomograph, located at the University of Bari (Italy). A 45-kV X-ray source was used with a current of 218 µA. A total of 1200 absorption radiographs were acquired over a 360 ° rotation with an angular step of 0.3 °. Random movement of the vertical axis and multiple-frame averaging were used to minimize the Poisson noise in the projection images. Beam hardening was reduced by the presence of a 0.5 mm Al-filter between the source and the detector. The nominal spatial resolution for the resulting model was 4.75 µm. The raw data were reconstructed into two-dimensional slice images using the software "NRecon, Skyscan, Belgium". Corrections for the beam-hardening effect and ring artifacts were also applied during the reconstruction process. Micro-CT data were analyzed using the software "CT-analyser, Skyscan, Belgium". Cathodoluminescence Cathodoluminescence images were collected on a Centaurus detector attached to a Hitachi S-3500N scanning electron microscope (SEM; School of Earth Sciences, University of Bristol). Samples were carbon coated prior to imaging. Accelerating voltages were varied between 10 and 20 kV to obtain the best quality images.
Despite recent advances, mineralization site, its microarchitecture, and composition in calcific heart valve remain poorly understood. A multiscale investigation, using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectrometry (EDS), from micrometre up to nanometre, was conducted on human severely calcified aortic and mitral valves, to provide new insights into calcification process. Our aim was to evaluate the spatial relationship existing between bioapatite crystals, their local growing microenvironment, and the presence of a hierarchical architecture. Here we detected the presence of bioapatite crystals in two different mineralization sites that suggest the action of two different growth processes: a pathological crystallization process that occurs in biological niches and is ascribed to a purely physicochemical process and a matrix-mediated mineralized process in which the extracellular matrix acts as the template for a site-directed nanocrystals nucleation. Different shapes of bioapatite crystallization were observed at micrometer scale in each microenvironment but at the nanoscale level crystals appear to be made up by the same subunits.
Three samples of (Tl,Sb,As)-rich pyrite from the ore deposits of southern Apuan Alps (Tuscany, Italy) 15were studied through a multi-technique approach in order to constrain the speciation and incorporation 16 mechanism of thallium in pyrite. High concentrations of Tl, Sb, and As were detected in all the studied 17 samples through laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). Average 18 Tl contents were 1,299 ppm, 1,967 ppm, and 2,623 ppm in samples from Sennari, Canale della Radice, 19 and Fornovolasco, respectively. The LA-ICP-MS time-resolved down-hole ablation profiles were 20 smooth indicating that Tl, Sb, and As are dissolved in the pyrite matrix, or occur in homogeneously 21 distributed nanoparticles (NPs). X-ray absorption spectroscopy (XAS) data revealed that Tl, Sb, and As 22 occurs as Tl + , Sb 3+ , As 3+ , and As 1-. In all the studied samples, bond distances and coordination numbers 23 for Sb 3+ and As 3+ are constant, whereas Tl displays a range of coordination numbers (~3 to ~6),
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