Gemological Institute of America

The growing interest in the spectroscopic properties of Type Ib diamonds has revealed several complexities associated with nitrogen (N)-related defects that have yet to be identified. One defect in particular, the Y-center, produces a characteristic spectrum in the N-region (∼1000-1400 cm−1) that is extremely common in the IR spectra of diamonds with a dominant Type Ib component. In this study, a suite of 178 Type Ib + IaA diamonds with variable N-aggregation states (%IaA) and N contents is examined to evaluate the effect of Y-center absorbance on the results obtained from standard deconvolution of the N-region. To do this, a new deconvolution routine is developed that incorporates the Y-center spectrum (obtained by decomposition of Type Ib spectra) and an updated spreadsheet (Caxbd_Inherit_2024-Ib) for processing the IR spectra of Type Ib diamonds is provided. It is shown here that neglecting Y-center absorption during least squares fitting of the IR spectra of Type Ib + IaA diamonds results in poor quality fits of the N region that may result in erroneous C- and A-center contents. The identity of the Y-center, and the relevant absorption coefficient, have not been constrained. However, several studies have shown that Y-centers are structurally related to single-substitutional N (called NS0 or C-centers), thus the Y-center contents are calculated using the C-center absorption coefficient. Using the new deconvolution method, it is shown that neglecting Y-centers may result in N-aggregation states that may vary by ±10 %IaA and total N contents (Ntot) that may be overestimated by >100 at.ppm. The samples studied here have an average Ntot of ∼100 at.ppm and errors in %IaA and Ni may be much larger for diamonds with higher Ni. Such errors translate to potentially significant discrepancies in the calculated mantle residence times on the order of hundreds of millions of years. Comparisons of the normalized Y-center content and %IaA show that Y centers are an intermediate defect that is produced from 0 to 40 %IaA at the expense of C-centers and then consumed from 40–100 %IaA to produce A-centers. A strong linear correlation with some IR peaks observed between 1400 and 1350 cm−1 (e.g., 1358 cm−1) is observed. Evidence supporting the assignment of such peaks to defects containing interstitial carbon and nitrogen (Ci and Ni) is described and suggests that the formation of Y-centers is driven by interstitial-assisted aggregation. Moreover, the Y-center itself may be an intermediate form of NS0 linked to Ci or Ni or larger interstitial complexes that become unstable with increasing N-aggregation (mantle residence time/temperature). Evidence for alternative hypotheses for the identity of the Y-center involving O- and Ni-related defects and X-centers are also discussed.

A calcite reference material (CCMb) derived from Carrara marble was developed for calibrating in situ mass fraction measurements of selected minor and trace elements (Mg, Sr) and the isotope ratios of carbon (δ 13 C) and oxygen (δ 18 O). Chemical and isotopic properties were characterised by bulk solution and in situ techniques, with ten laboratories participating in an analytical round‐robin. Grains of CCMb were analysed by ion microprobe (SIMS) against a suite of calcite reference materials, including international reference material IAEA‐603, to evaluate the influence of minor amounts of Mg on the instrumental mass fractionation of δ 18 O values. CCMb consists of an assemblage of tightly interlocking calcite crystallites measuring 100–300 μm across. Fluid‐inclusion trails are abundant along crystallite grain boundaries. An offset was observed between δ 18 O values of CCMb determined by gas‐source isotope ratio mass spectrometry (GS‐IRMS) and SIMS measurement. The results of this study indicate the offset could be related to the presence of isotopically light calcite material in grain boundary regions and micro‐fissures, domains only several micrometres thick. When used for calibrating SIMS measurements, CCMb should be assigned a reference δ 18 O value of +28.81 ± 0.15‰ (VSMOW, 2 s, based on SIMS results), representative of the integrated crystallite volume less the contribution of the inferred low δ 18 O phase occupying intercrystalline space. Measurements of δ 13 C by ion microprobe reproduced the bulk‐grain, GS‐IRMS derived value of +1.95 ± 0.06‰ (VPDB, 2 s ). This study did not find evidence for matrix effects related to Mg‐substitution at mass fractions ≤ 3000 μg g ‐1 . The preferred reference values for the Mg and Sr mass fractions in CCMb are 0.36 ± 0.05% m/m (2 s ) and 156 ± 8 μg g ‐1 (2 s ), respectively.

NeuXtalViz (Neutron Single-Crystal Visualization) is a Python-based software package developed at Oak Ridge National Laboratory to provide interactive three-dimensional visualization and analysis tools for single-crystal neutron diffraction experiments. Built on the Mantid framework for data reduction, and leveraging PyVista and Matplotlib within a Python Qt environment, NeuXtalViz adopts a model-view-presenter architecture that separates the user interface from the core processing components. The software provides a unified interface for tasks central to single-crystal diffraction, including UB-matrix determination, experiment planning, visualization of normalized reciprocal-space volumes, and real-space crystal-structure calculations. It also integrates with widely used community tools and has been deployed on instrument and analysis servers, where it is now being adopted by instrument teams and users. By embedding advanced three-dimensional visualization directly into the experimental workflow, NeuXtalViz enhances the planning, execution, and analysis cycle for single-crystal neutron diffraction experiments, while providing a flexible framework for future development.

Over the past two decades, the Gemological Institute of America (GIA) has documented an exponential increase in the quantity, size, and quality of gem diamonds grown by chemical vapor deposition (CVD) and, therefore, these products’ ability to be commercialized on a large scale. This talk is intended to provide a comprehensive overview of these developments and summarize novel CVD-grown diamonds that may become more common in the future. During the last five years, there have been relatively few changes in laboratory-grown diamonds indicating that developments have largely stabilized for now. We’ll explore the major trends observed by GIA since 2007, the year the laboratory began issuing synthetic diamond grading reports. These trends include the shift towards larger and colorless stones. CVD products now dominate the supply of laboratory-grown diamonds submitted for grading reports, with the majority of these also undergoing post-growth high-pressure, high-temperature (HPHT) treatment to reduce their color. This talk will discuss methods and strategies employed by gemological laboratories for identifying CVD-grown diamonds and distinguishing them from their natural and HPHT-grown counterparts. Finally, we present an array of CVD-grown gem diamonds that are currently unusual; however, these may become more common in the future.