Study on the Influence of Porosity of the Nacre Layer on the Luster and Surface Roughness of Chinese Large Freshwater Nucleated Pearl

The Chinese large freshwater nucleated pearl has become popular for its unique appearance throughout the international jewelry market in recent years. However, its quality evaluation mostly depends on appearance observations, and the influence of the nacre layer’s internal microstructure on the gemstone’s appearance needs further investigation. In this study, light reflectivity, surface height unevenness parameters and porosity of the nacre layer were measured by chroma meter, laser scanning confocal microscope and X-ray computed tomography (μ-CT), which quantitatively described the characteristics of luster, surface roughness and structure compactness of the nacre layer. It was found that the porosity of the nacre layer had a significant influence on appearance features, with an increase of porosity showing more surface blemishes (higher surface roughness parameters) and weaker luster (lower reflectivity). Related results can provide reference for the scientific and quantitative evaluation of pearl quality

Identification of Jadeite Filled with Inorganic Materials Using UV Fluorescence, Infrared Spectroscopy and LIBS Techniques

BACKGROUND: Through visiting the jadeite market, the existence of inorganic material-filled jadeite is known, but there is a lack of identification basis due to rare references.OBJECTIVES: To understand the identification characteristics of inorganic material-filled jadeite.METHODS: Two types of inorganic materials, water glass and silica sol, were used to fill low-grade jadeite in the simulation experiment. Conventional gemological tests, fluorescence image observation with DiamondViewTM, Fourier transform infrared (FTIR) spectroscopy, and laser-induced breakdown spectroscopy (LIBS) were used to test the inorganic filled jadeite samples.RESULTS: The transparency, color, density and structure of jadeite were improved after filling. Under the DiamondViewTM, the jadeite particles in the sample showed green fluorescence, and the filling around the cracks and between the particles displayed blue fluorescence with non-uniform distribution. Mid-infrared reflectance spectrum analysis showed that the spectra of silica sol and water-glass were slightly different from each other. The absorption peaks of the samples filled with inorganic materials at 1162cm-1, 1070cm-1, 949cm-1, 579cm-1, 529cm-1 and 470cm-1 gradually weakened, and the peak shape gradually became smooth or disappeared. In addition, the differences between the jadeite and inorganic filled jadeite can be determined by the near-infrared spectral morphology and the shape of the absorption peak changed in the range of 7062cm-1, 5204cm-1 and 4537cm-1. The laser-induced breakdown spectroscopy demonstrated that the content of the silicon in the jadeite filled with silicon sol or sodium and potassium water-glass was higher. The high potassium content was an important feature for the jadeite filled by sodium and potassium water-glass.CONCLUSIONS: The samples effect of the simulation experiment needs to be improved, but the identification characteristics of the filled jadeite with inorganic materials are recognized, which has caused a further breakthrough in the enhancement and treatment of jadeite identification

Analysis of Abnormal Birefringence and Graphite Inclusions in Zimbabwean Diamonds

BACKGROUND: The Marange diamond deposit in Zimbabwe is characterized by producing mixed-habit (octahedral and cuboid) diamonds. Graphite inclusions in these diamonds only exist in cuboid sectors. The morphological and distributional characteristics of graphite inclusions and the abnormal birefringence and strain characteristics of diamonds can reflect the geological process experienced by diamonds from the beginning of crystallization to being transported to the Earth's surface. Therefore, the study of diamonds and graphite inclusions in Zimbabwe can provide comparative data for diamonds from other deposits. Besides, due to the peculiarity of growth habits, detailed analysis would be of great value to help understand the behavioral differences of diamonds with different growth habits in geological processes.[LM]OBJECTIVES: To determine if graphite inclusions in Zimbabwean diamonds are syngenetic or epigenetic, and to reveal the relationship between graphite inclusions and the infrared absorption spectrum, Raman scattering spectrum as well as birefringence and strain characteristics of diamonds.METHODS: The growth structure and growth sectors of Zimbabwean diamonds were observed by DiamondViewTM image system. The morphological and distributional characteristics of graphite inclusions and abnormal birefringence in diamonds were analyzed by scanning electron microscopy (SEM) and polarized light microscopy. Analysis of distribution and relative concentration of impurity elements in different growth sectors was conducted by infrared spectroscopy. Strain characteristics of diamonds in different growth sectors were analyzed by Raman spectroscopy and projection diagram of corresponding results.RESULTS: Graphite inclusions in cuboid sectors of Zimbabwean diamonds were syngenetic-epigenetic inclusions located in directional elliptical cracks. According to infrared spectra of different growth sectors, cuboid sectors showed stronger infrared absorption related to elemental hydrogen, while octahedral sectors showed stronger absorption related to elemental nitrogen. This enrichment of different impurity elements leading to abnormal birefringence was mainly related to cracks and different growth sectors in diamond. The Raman shift of LO=TO band in octahedral sectors was 1332.05-1332.20cm-1, the FWHM was 4.21-4.37cm-1, which corresponded to stress of 0.06-0.27GPa. The Raman shift of LO=TO band in cuboid sectors was 1331.93-1332.47cm-1, the FWHM was 3.67-4.08cm-1, which corresponded to stress of 0.01-0.64GPa. In general, the residual stress and strain were greater in cuboid sectors.CONCLUSIONS: The determination of the orientation of graphite inclusions in mixed-habit diamonds in Zimbabwe, provides new evidence to prove their syngenetic-epigenetic nature, and reveal the difference in the strain characteristics of diamonds in the two growth regions. This research is helpful for understanding the formation environment of diamonds in Zimbabwe and of different diamonds. The differences in physicochemical properties are of great significance

Spectroscopic Identification of Amber Imitations: Different Pressure and Temperature Treatments of Copal Resins

Copal resins can be treated with heat and/or pressure to imitate ambers in the gem market. To explore the effects of different modification conditions on post-treatment spectral changes, five experimental methods with different temperature–pressure parameters were designed to modify two types of copal resins. The treated copal resins were examined by infrared, Raman and nuclear magnetic resonance spectroscopy. Results indicate that all the treatment methods simulate the maturation process, with spectral characteristics becoming more similar to those of ambers. Multi-stage heat–pressure treatment has the most significant effect on Colombia and Madagascar copal resins, with their spectra being similar to those of Dominican and Mexican ambers. Rapid high-temperature treatment at 180 °C modified the Borneo copal resin, with its infrared spectrum developing a “Baltic shoulder” resembling that of heat-treated Baltic amber. Even though there are many similarities between treated copal resins and natural ambers, they can still be distinguished by spectroscopic methods

Spectroscopic Study of the 3107 cm−1 and 3143 cm−1 H-Related Defects in Type Ib Diamonds

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

Morphological and Surface Microtopographic Features of HPHT-Grown Diamond Crystals with Contact Twinning

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

Spectroscopic Study of the 3107 cm⁻¹ and 3143 cm⁻¹ H-Related Defects in Type Ib Diamonds

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

Study on the Microstructure and Spectra of Regrown Quartz Crystals from Chinese Jewelry Market

Regrown quartz crystals consist of the natural section and the synthetic section grown by hydrothermal technique, which has become popular on the Chinese jewelry market in recent years. Similar gemological properties to those of natural quartz have brought challenges to gem identification and also new questions to scientific research. In this study, microstructure and spectral characteristics of the two sections of regrown quartz crystals were investigated by three dimensional computed tomography system and infrared spectroscopy. Results showed that the natural section has a higher porosity and there are also many micron- to millimeter-sized pores on the interface of the two sections. Different infrared absorption peaks of the two sections at the 3300–3600 cm−1 range were mainly attributed to the different existence state of OH groups. The distinction of microstructure and spectral characteristics between the natural and synthetic sections indicate their different growth condition. Compared with natural quartz, a relatively stable growth environment during the synthetic process leads to a lower porosity and the alkali growth solution could result in the change of the existence state of OH groups in the regrown quartz crystals

Chinese Colorless HPHT Synthetic Diamond Inclusion Features and Identification

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