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Birefringence in diamond is an optical phenomenon related to strain and various defects in crystal lattices. Despite extensive investigations being done to characterize and quantify it, there is still controversy about its origin in diamond lattices. Here we report the relationship between the distribution of birefringence patterns observed under cross-polarized light, strain features analyzed by Raman mapping, and the impurity characteristics revealed by Fourier transform infrared spectroscopy (FTIR) mapping in natural mixed-habit diamonds. It was deduced that the plastic deformation was enhanced with higher tensile residual stress, and nitrogen and VN 3 H defects were more enriched as a result of the temperature increase during crystallization, at growth bands showing straight birefringence patterns and the relative enrichment of graphite inclusions. These results provided solid data and insights for birefringence-related properties in diamond and correlated the occurrence of birefringence with diamond spectroscopic properties, which promoted the understanding of the formation of birefringence in natural diamonds and would be helpful for the synthesis of high-quality, birefringence-free diamonds. [ABSTRACT FROM AUTHOR]

Hydrogen-related infrared absorption bands in natural diamonds have been extensively investigated and widely used to identify natural, treated, and synthetic diamonds grown by high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) techniques. However, the evolutional behavior of the hydrogen-related defects and the relationship between the hydrogen-related and nitrogen-related defects in natural and HPHT-treated Ib diamonds are unclear. In this article, the hydrogen-related defects, particularly the infrared absorption bands of 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds and HPHT-treated natural diamonds, were systematically investigated using spectroscopic techniques. It was found that the 1405 cm−1 absorption intensity was directly proportional to the 3107 cm−1 absorption intensity; the 3143 cm−1 absorption intensity increased with the increase in the 3107 cm−1 absorption intensity, but there was no strict linear relationship between them. The 3143 cm−1 band was not only related to the intensity of the 3107 cm−1 but also related to the value of NC/NA in natural diamonds. When the value of NC/NA was less than one, the 3143 cm−1 band was more pronounced. After high-temperature annealing, the absorption intensities of the 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds became stronger. However, in HPHT synthetic diamonds, only a 3107 cm−1 defect was introduced with the increase in the A centers in the diamonds. The difference and the detectability of the 3143 cm−1 and 3107 cm−1 bands investigated could be efficiently used to identify natural type Ib diamonds from their counterparts, including the synthetic diamonds and the HPHT-treated diamonds. [ABSTRACT FROM AUTHOR]

Gem-grade twinned high-pressure high-temperature (HPHT) synthetic diamond crystals are rare. Hence, few investigations on their morphological features and formation have been reported. In this article, the morphological and surface microtopographic features of HPHT synthetic-diamond crystals contact twinning is detailed and investigated. It indicates that twins of diamond forming and nucleating during the early stages of the growth and the development of {100} and {111} growth sectors on either side of such boundaries proceeds independently, which affects the final morphology of the diamond crystals. According to the different features of crystal macroscopic morphological properties, two kinds of twin model have been established. The formation of twin crystals changed the lattice of diamonds with face-centered cubic dimensions. The type of diamond lattice at the twin boundary is hexagonal and closely packed, which has potential for further developing the application of synthetic diamond twin crystals. [ABSTRACT FROM AUTHOR]

Chinese HPHT diamonds have improved dramatically in recent years. However, this brings a challenge in identifying type IIa colorless diamonds. In this study, eleven HPHT and three natural, colorless, gem-quality IIa diamonds were analyzed using magnified observation, Raman, PL and chemical element analysis. The results show that only HPHT samples possessed kite-like inclusions and lichenoid inclusions, as verified by their complex Raman spectra (100–750 cm−1). Through PL mapping, HPHT and natural IIa diamonds were distinguished by their growth environments, which were reflected by PL peaks at 503, 505, 575, 637, 693, 694 and 737 nm. The chemical components of HPHT IIa diamond carbide inclusions are mainly Fe, Co, Ni and Mn, but those of Natural IIa are mainly Fe and Ni. As a result, the chemical components can be used to distinguish a natural colorless IIa diamond from a synthetic diamond. [ABSTRACT FROM AUTHOR]

Trigons on the surface of diamonds are correlated with defects in their crystal lattices. However, due to the rarity of HPHT diamond octahedrons. Few studies have focused on surface features of them. Here, we made detailed observation and description of as-grown surface features on 27 HPHT diamond octahedrons produced from China, and reported new features of jagged steps of trigons, 90° oriented trigons, and residual hillocks on diamonds. The formation of these features was discussed, and the relationships between parameters of trigons and hillocks were thoroughly investigated. It was found that the depth of trigons on these HPHT diamond octahedrons was smaller than 1 μm, and most positive f/b trigons showed the depth limit of 0.2 μm. Besides, correlations between the diameter, depth, and inclination angle of trigons demonstrated that the development of trigons displayed distinctive characteristics in different stages: In the beginning, when the trigons were relatively small (diameter < 5 μm), the increasing rate of depth was larger than that of diameter, while when the trigons enlarged to some extent (diameter > 20 μm), their diameter would develop faster than their depth in the following process. This study expanded our cognition of surface features on diamond, provided solid systematic data for trigons on HPHT diamond octahedrons, and furthered comprehension of the formation process of trigons on the surface of diamonds, which has reference significance for evaluating and improving the quality of synthetic diamond crystals. [Display omitted] • Jagged steps of trigons and trigons with the orientation perpendicular to {111} surface planes were observed. • Residual triangular hillocks with trigons in them were reported. • Relationships between parameters of trigons and hillocks were discussed. • Different developing trends of trigons with different size were determined. [ABSTRACT FROM AUTHOR]

The article focuses on a test conducted to 21 samples of black-and-white diamond jewelry using Fourier transform infrared (FTIR) and Raman spectroscopy. It is said that about 10 of the jewelry samples were found to have black synthetic moissanite. Raman spectroscopy revealed that the inclusions in black synthetic moissanite were determined as crystalline silicon. The research "Synthetic Moissanite: A New Diamond Institute" by K. Nassau et al. noted that such moissanites were not developed through a so-called seeded sublimation process.

The article presents abstracts on gems which include a description of a valuation model for cut diamonds, presentation of a dataset for conflict diamonds and a study on disease status of gem worker's silicosis.