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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]

Natural blue sapphire is a gem species of corundum, which has high economic value due to its beauty and rarity. Color is the most important factor affecting the price of sapphire and mainly caused by trace elements. However, there is little quantitative data currently available to demonstrate the correlation between trace elements and colorimetric parameters of natural blue sapphire. In this study, the UV‐Vis‐NIR spectra and colorimetric parameters were collected by UV‐Vis‐NIR spectrophotometer while the chemical composition was analyzed by laser‐ablation inductively coupled plasma mass spectrometry. The results show that the content ratio of (FeOT + TiO2)/MgO has negative correlation with b* but positive correlation with Cab*, illustrating its obvious effect on the blue color saturation of natural blue sapphire. In addition, the existence of Cr can produce purple hue and the content of Cr shows positive correlation with hue‐angle hab only in the low range (5‐15 ppm), which implies the content of Cr has a limited influence on the hue of natural blue sapphire and the effect may be more complicated as the content of Cr increases above 15 ppm. This investigation can provide quantitative data for scientific color grading and additional applications of natural blue sapphire. [ABSTRACT FROM AUTHOR]

Zultanite is the commercial name of a gem‐quality transparent diaspore that exhibits an obvious color change when exposed to different light sources. It usually appears green under daylight and red under incandescent light. This optical feature makes zultanite valuable, and the study of the spectral characteristics, as well as chemical composition, of zultanite can increase our understanding of the associated color change mechanism. Spectral transmittance curves for zultanite exposed to nonpolarized light emitted by CIE standard illuminants D65 and A show that the color change phenomenon is related to the optical characteristics of light sources. The colorimetric parameters in the CIE 1976 L*a*b* uniform color space system illustrate that the color change exhibited by zultanite is an example of the alexandrite effect, which can be quantitatively described by the significant change of a* and h° parameters. These findings and the results of chemical element analysis by X‐ray fluorescence and X‐ray photoelectron spectroscopy imply that electron transitions between different energy levels involving the 3d orbitals of the trace elements Fe3+ and Cr3+ in zultanite give rise to the relatively high transmittance observed in the green region (around 500 nm) and the orange‐red region (600‐780 nm) of visible light. Thus, the difference in the spectral power distributions of different ambient light sources greatly influence the color of zultanite, making zultanite show green under daylight which is richer in the green light and turns red under incandescent light in which the orange‐red light dominates. Summary: The main contributions of this article can be summarized as follows: The colorimetric parameters of zultanite illustrate that its color change phenomenon is an example of the alexandrite effect.The trace elements Fe3+ and Cr3+ are the essential factors that cause the alexandrite effect, which give rise to the relatively high transmittance observed in the green and orange‐red regions of visible light.This article will inspire deeper research on the optical properties and application of hydroxides. [ABSTRACT FROM AUTHOR]

The combustion characteristics of municipal sewage sludge samples with five different initial water contents (5.02, 8.21, 17.33, 27.45 and 37.85%) were assessed by using a thermogravimetric analysis approach. The ignition temperatures of the samples increased with increasing the heating rates and their initial moisture content. Ignition, burnout and comprehensive performance indices of the samples increased with decreasing their initial moisture contents. Between heating rates of 20 and 80 K min, the average ignition, burnout and comprehensive performance indices of the sample with initial moisture content of 5.02% were about 1.2, 2.2 and 0.9 times more than those of the sample with initial moisture content of 37.85%. The average activation energies for the samples with 5.02, 8.21, 17.33, 27.45 and 37.85% moisture contents were 146.59, 148.02, 155.13, 156.70 and 168.39 kJ mol. There were certain linear relations among two main kinetic parameters for the samples with different moisture contents and their main combustion stages. [ABSTRACT FROM AUTHOR]

This study investigates nonisothermal co-drying kinetics of two typical biomasses (cornstalk and red pine) with lignite in the presence of a nitrogen atmosphere using a thermal gravimetric analysis technique. The drying rate can be increased by either decreasing the blending ratio of biomass or increasing the heating rate. The activation energies of cornstalk/lignite blends and red pine/lignite blends in the two falling rate periods are less than that of their parent samples. In the first falling rate period, the dominant mechanisms of drying for lignite are described by the Avrami–Erofeev equation (n = 1.5), while the mechanisms for the cornstalk, red pine, and mixture samples are fitted to the Mample equation (n = 1.0). In the second falling rate period, the mechanisms are described by the Avrami–Erofeev equation (n = 1.5 orn = 2.0). The general kinetic compensation effect correlations are obtained for all samples within heating rates of 10–30°C/min. Significant synergistic interactions between the Chinese lignite and cornstalk or red pine are detected during co-drying. [ABSTRACT FROM AUTHOR]

The impurity transition element chromium Cr3+ in ruby can be excited to high energy levels by absorbing visible light. When the excited Cr3+ returns to ground state through an intermediate energy level, the ruby emits red light as fluorescence. The fluorescence of ruby is actually caused by visible light, not by ultraviolet. The color of ruby is attributed to both the absorption and the fluorescence. The spectrum of a natural ruby under visible light is directly measured by a dual integrating sphere spectrometer. The measured spectrum includes both the spectral reflectance and the fluorescence caused by visible light. This study confirmed that the red fluorescence of ruby is indeed caused by visible light, not by ultraviolet radiation. In addition, average color of the ruby is calculated from the measured spectrum, and true color grade is also obtained by the artificial intelligent software of the spectrometer. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 328-333, 2013 [ABSTRACT FROM AUTHOR]

The components and evolution of subcontinental lithospheric mantle beneath the North China Craton and the Yangtze Craton is a current topic in the geological study of China and the carbon isotopic composition of diamond is one of the most direct probes into cratonic lithospheric mantle processes. In this paper, in-situ SIMS (Secondary Ion Mass Spectrometry) techniques were used to analyze the carbon isotope compositions at different internal growth zones of diamonds from Shandong and Liaoning in the North China Craton and Hunan in the Yangtze Craton. It was found that the carbon isotopic range of diamonds from the North China Craton are rather distinct from those of the Yangtze Craton; the former has a range of −6.0/‰ to −2.0‰ (relative to VPDB) with an average value of −3.0‰ in their core areas, which is consistent with global peridotitic diamonds; the diamonds from the Yangtze Craton, however, have a carbon isotopic range from −8.6‰ to −3.0‰ with an average value of −7.4‰ in their core areas, being more consistent with global eclogitic diamonds. The variations of carbon isotope ratios between different internal growth zones in individual diamonds were different in the three diamond localities studied. There was a clear correlation between changes in carbon isotopic composition and phases of diamond dissolution and new growth, while no correlation was observed between δC and internal inclusions. The variations suggest that the carbon isotopic compositions of mantle fluids were changing during the process of diamond crystallization, and that the heterogeneity of the carbon isotopic composition in mantle carbon reservoirs was a more important factor than carbon isotope fractionation in controlling the carbon isotopic compositions and their variation in diamonds. In addition, the preliminary results of in-situ nitrogen analyses demonstrated that the variation of carbon isotopic compositions between the core and outer growth zones does not correlate with nitrogen abundances, implying either that diamonds crystallized in an open environment or that the carbon isotopic composition and nitrogen contents in mantle fluids were controlled by other, not yet understood factors. The experimental results provide hints that the isotopic composition of carbon and its original sources were different in metasomatic fluids controlling diamond formation in the mantle beneath the North China Craton and the Yangtze Craton. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, the pole figures plotted from X-ray diffraction data are employed to analyze the orientation of hydroxyapatite in ivory and mammoth ivory for the first time. The results present evidence of the lamellar structure and the hydroxyapatite appeared as tabular. A preferred orientation of hydroxyapatite was revealed in terms of the calculated orientation factor and the characteristics found in the pole figures. The c-axes of hydroxyapatite are mainly oriented along the growth direction. Both a-axes are on the left of the angle bisector of Retzius. Approximately 25–30° separates the a-axes and the angle bisector of Retzius in ivory, whereas the figure is approximately 10–15° in mammoth ivory. Our work is significant in providing more accurate knowledge of the shapes and organizational state of bio-mineral crystals and providing insight into crystal formation and development in bio-mineralization. [ABSTRACT FROM AUTHOR]