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BACKGROUND In order to quickly identify and screen high pressure and high temperature (HPHT) grown synthetic diamonds, a lot of research about their luminescent and spectral characteristics has been done. However, the comparative analysis is lacking, and less attention is paid to electrical and magnetic properties. OBJECTIVES To summarize the spectral characteristics and investigate the electrical and magnetic properties of HPHT synthetic diamonds systematically. METHODS Conventional gemological observation, high precision spectroscopy and electrical conductivity and magnetism testing were used for comparative analysis of 49 colorless and yellow samples. RESULTS The residual metal catalysts, including iron, cobalt, and nickel, caused the ferromagnetism of diamonds. All of the HPHT synthetic diamond samples could be attracted by the magnetic bar with magnetic intensity up to 12000Gs. The colorless samples were type Ⅱa+Ⅱb diamonds. The presence of boron led to its good conductivity, and the conductivity increased with increased boron content. The yellow samples were Ib+IaA type diamonds, and about one-third of the single nitrogen was converted into A aggregate. The synthetic diamond had undergone high temperature annealing treatment after growth. The ubiquitous presence of boron, and the presence of nitrogen mainly as single atoms and A aggregates led to the characteristic infrared spectra of HPHT synthetic diamonds. HPHT synthetic diamonds often contained crystal lattice defects caused by impurity elements such as nitrogen, nickel and silicon, which led to characteristic photoluminescence spectra. Colorless samples showed strong blue-green fluorescence and phosphorescence, whereas yellow samples had green fluorescence, with obvious cube-octahedron patterns. CONCLUSIONS Spectral and luminescent characteristics are still an important basis for screening and identification of HPHT synthetic diamonds. HPHT synthetic diamonds under the current growth technology also have obvious differences from natural diamonds in both conductivity and magnetism, which can be used as an auxiliary basis for rapid identification.

BACKGROUND Spectroscopic characteristics for brown colored Type Ⅱa diamonds treated by high pressure high temperature (HPHT) processes have been investigated extensively. However, almost no reports are available on the variation of the spectroscopic features for the type Ⅰa Cape series brown colored diamonds treated by HPHT processes. OBJECTIVES To help the laboratory to resolve the origin of yellow diamonds. METHODS The ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy were used to analyze the spectral features for the samples before and after each treatment. RESULTS The color of the diamonds changed from grayish brown to brownish yellow after the HPHT process. Meanwhile, the FTIR/UV-Vis absorption, as well as the photoluminescence was also greatly changed. Besides the 415nm and the 477nm absorption peaks, the treated diamonds also display H3 defect (503.2nm) and the gradually increasing absorption from 550nm to shortwave, resulted in the color changing from grayish brown to brownish yellow. In the mid-infrared region, the three peaks of 1498, 1520 and 1547cm-1 become a broad band centered at 1498cm-1 after treatment, and the photoluminescence spectrum displayed two distinct defects-H3 (503.2nm) and H2 (986.2nm). CONCLUSIONS The spectroscopic features provide a basis for accurate identification of HPHT-treated type Ⅰa Cape series brown diamonds in gem laboratories, and increase understanding of the variation mechanism of the nitrogen and hydrogen related lattice defects in the diamonds during the HPHT processes.

BACKGROUND As the world's largest producer of synthetic diamonds, China accounts for more than 90% of the world's total production, of which high pressure-high temperature (HPHT) synthetic diamonds are dominant. Previous scholars have conducted many studies on analytical methods and property analysis of HPHT synthetic diamonds. However, the research on the pickling process after the growth of HPHT synthetic diamonds and the internal and external micro-structures after pickling is still insufficient. OBJECTIVES To characterize 118 synthetic diamonds produced in China by high temperature and high pressure method. METHODS The HPHT synthetic diamonds were observed by laser scanning confocal microscopy (LSCM) and ultra-depth-of-field 3D microscopy, and the dark inclusions in these micro-structures were qualitatively analyzed by laser Raman spectroscopy. RESULTS Three structure types were found. Step-like growth structures with certain angles revealed the crystallographic characteristics of HPHT synthetic diamond poly-crystals. Near-parallel linear scratches reflected the contact relationship between diamond grains in the growth chamber. The 'rope-tied' structures reflected the growth rate of HPHT synthetic diamonds. CONCLUSIONS The micromorphology of these diamond surfaces reflects the growth conditions and environment of HPHT synthetic diamond gradient high temperature and continuous high pressure, which is of significance for the identification of HPHT synthetic diamonds.

BACKGROUND Overgrowth diamond refers to the product of thick CVD synthetic diamond layer grown on a natural diamond with the whole appearance. Since overgrown diamonds contain information on the nitrogen impurities of natural diamonds, traditional synthetic diamond screening methods and testing procedures are no longer applicable to the detection of overgrown diamonds. OBJECTIVE To gemologically test an overgrowth diamond sample in order to investigate the full identification features and to propose the optimum detection strategy. METHODS Minspecting, screening instruments testing, UV-Vis/FTIR/PL spectra examinations, as well as fluorescence and phosphorescence observation under deep UV excitation are carried out. RESULTS The sample cannot be identified by traditional microscopic observation, diamond instrument screening, and infrared spectra measurement. The sample has a distinct boundary that is separated by different luminescence under DiamondViewTM. The upper layer displays red fluorescence and greenish blue phosphorescence, while the lower layer shows deep blue fluorescence and no phosphorescence. Infrared spectroscopic analysis shows that the upper layer is type Ⅱa and the lower layer is type Ⅰa diamond. The UV-Vis absorption and photoluminescence spectra confirmed the coexistence of N3 centers and a high level of[Si-V]- defects in the diamond. CONCLUSIONS It was confirmed that the lower part of the sample is natural and the upper part of the sample is CVD synthetic layer with a thickness around 740μm. The first overgrowth diamond reported domestically was compared to the same type of samples reported abroad. The existence of a boundary are missing and the thickness of the CVD layer increased significantly in this sample. The innovative application of the multidirectional luminescence imaging and spectroscopic analyses is the key to laboratory testing of overgrowth diamond.

BACKGROUND The Omixia nephrite deposit is located in the middle West Kunlun Orogenic belt. The deposit is hosted in Mg-skarn between granite and magnesian marble. The deposit is large and has a long exploration and large scale, but the research on ore genesis and age remains lacking. OBJECTIVES To understand the genesis and upper age of the Omixia nephrite deposit by collecting and analyzing typical samples. METHODS Petrological and bulk rock methods are used to investigate the ore genesis, whereas the age of the deposit is constrained by LA-ICP-MS U-Pb zircon dating of nephrite. RESULTS Petrographic observation shows that nephrite formed at multiple stages. The REE patterns of the nephrite indicate low REE concentration with the average ∑REE of 7.228 μg/g, and strong negative Eu anomalies (δEu=0.58-0.73) with declined LREE and flat HREE. Zircon in nephrite has 206Pb/238U ages ranging from 411.1±5.3 Ma to 489.6±10.5 Ma. CONCLUSIONS Omixia nephrite deposit is a typical contact metasomatic Mg-skarn nephrite deposit. The formation of gem-grade nephrite jade has undergone multiple processes, tremolite mineralization, diapolitization, fine granulation, and recrystallization. The formation age of this nephrite deposit is similar to other nephrite deposits in West Kunlun, and they are formed at the Late Caledonian and Early Hercynian. This study is helpful to understand the formation mechanism of nephrite in West Kunlun area of Xinjiang and provides new basic data for geological research in the West Kunlun.

Research on different types of brown diamonds under high temperature and high pressure and their structural characteristics is one of the most difficult and important issues in diamond research. Previous studies on hydrogen-rich diamond mainly focused on its special growth structure and the formation environment, but rarely on the characteristics of hydrogen-rich diamond after high temperature and high pressure treatment. The spectral characteristics of the hydrogen-rich diamonds before and after high temperature and high pressure treatment, including Infrared Spectra, UV-vis Absorption Spectra, and Photoluminescence Spectra were compared and their identification characteristics were studied. Results show that the spectroscopic features are different for the samples before and after the high temperature and high pressure treatment, epecially for infrared spectra. Absorption peaks related to H and N at 3310 cm-1, 3232 cm-1, 3189 cm-1 weakened obviously or even disappeared. Moreover, the absorption peak at 2688 cm-1 related to isolated nitrogen appeared. In the UV-Vis absorption spectrum, the non-selective absorption in treated brown diamonds became the typical isolated nitrogen absorption, which means that the absorption of 550 nm to shortwave and the absorption of the center of N3 (415 nm) increased obviously. Therefore, the diamond changed from the original brown to yellow. The photoluminescence spectra before and after treatment of diamonds also vary with the types of nitrogen-related defects, peak intensities, and defect combinations. The spectral characteristics obtained not only provide a basis for the accurate identification of yellow, hydrogen-rich diamonds treated by high temperature and high pressure, but also provide a theoretical basis for explaining the change mechanism of hydrogen-and nitrogen-related lattice defects under high temperature.

Jade-like cryptocrystalline-microcrystalline vein quartzite is called quartzite jade in the jewel business of China. Color is the main criteria for the value of quartzite jade, and therefore studying the coloration mechanism is very important for the color evaluation index and ore genesis. Previous studies have shown that the accurate information of color causing minerals cannot be acquired. The synchrotron radiation techniques, BL15U1 in SSRF equipped with μ-XRF and μ-XRD at SSRF were used for studying the color causing minerals in vein quartzite and are reported in this paper. It was found that yellow vein quartzite is colored by goethite (characteristic diffraction peaks at 0.49574, 0.41594, 0.26887, 0.25705, 0.25189, 0.24510, 0.21806, 0.17133 nm), whereas red quartzite is colored by hematite (characteristic diffraction peaks at 0.36774, 0.27091, 0.25200 nm). Yellow-red quartzite is colored by both goethite and hematite and hematite has a stronger coloration ability than goethite. This study provides direct data of the color causing minerals in quartzite jade, which is useful for discussing the crystallization conditions and the coloration mechanism, and also helpful for the quality evaluation of quartzite jade.

Natural diamonds commonly contain polymeric nitrogen and have complex growing textures, whereas synthetic diamonds do not contain nitrogen or do contain single nitrogen and have typical growing textures related to the synthetic process. Using these characteristics, natural and synthetic diamonds can be distinguished. However, effective identification on melee-sized diamonds or mounted jewelry is not feasible by conventional instruments. A multi-spectral induced luminescence imaging system, GV5000 has been invented, and is described in this paper. Through improving the excitation light source, the light filter, the device configuration, and testing methods, the fluorescence and phosphorescence features of multiple melee-sized diamonds (≥0.002 ct) can be observed simultaneously. An efficient and precise method to identify colorless melee-sized natural and synthetic diamonds on the basis of the luminescent characteristics has also been established. 9015 samples were analyzed by GV5000 and screening results were checked by infrared spectroscopy, and photoluminescence spectroscopy, 97% of the natural diamonds display blue fluorescence without phosphorescence. Moreover, the luminescence of synthetic diamonds is different from that of natural ones. This new method erases the influences of size and shape of samples and increases the accuracy and efficiency of the identification on melee-sized diamonds. The screening rates of natural and synthetic diamonds are as high as 97% and 100%, respectively.

Melee-sized colorless HPHT synthetic diamonds mixed with natural diamonds in jewellery have been reported by gem testing laboratory. It was noted that the differences of the fluorescence and phosphorescence between natural and synthetic diamonds are the key features for quick screening in mixed diamonds. However, it is difficult to completely distinguish the two only by the differences of fluorescence and phosphorescence. In this paper, 5 colorless gem-quality HPHT synthetic diamonds were systematically investigated and characterized using mutiple spectroscopic techniques, together with traditional gem testing techniques. It was found that 5 samples display no, or weak, 270 nm absorption band at the UV-Vis spectra, and the lower the color grade, the stronger the 270 nm absorption band. Infrared absorption spectra showed that all samples contain boron. The photoluminescence spectra revealed that the colorless HPHT synthetic diamonds contain N, Ni or Si-related lattice defects. Under irradiation of the ultra-short wavelength light, all samples phosphoresced strongly with blue-green color. Typical octahedral and cubic growth patterns can be clearly observed under the DiamondViewTM imaging system. Although there are some differences between the samples, the HPHT synthetic diamonds can be accurately identified through careful analysis combining all features, particularly the spectral charateristics of phosphorescence and fluorescence, FTIR, UV-Vis, and photoluminescence spectra.

Quartzite jade is composed of α-quartz and another silica phase, moganite, which forms under low pressure and low temperature conditions. At present, there are few studies on the relationship between the relative content of moganite and the crystallinity of quartzite jade. In this study, some quartzite jade samples from four locations in China(Longling, Yunnan province; Huoshan, Anhui province; Hezhou, Guangxi Zhuang Autonomous Region, and Alxa League, Inner Mongolia Autonomous Region), were analyzed by Raman Scattering Spectroscopy, Infrared Absorption Spectroscopy and X-ray Powder Diffraction techniques. The results showed a negative correlation between the relative content of moganite and the crystallinity of quartzite jade. The higher the relative content of moganite, the lower is the crystallinity index of quartzite jade. The relationship of the intensity ratio of 502 cm-1/465 cm-1 in the Raman scattering spectrum and the crystallinity index of quartzite jade, could be expressed by the equation of Y=-0.36X+6.93(the correlation coefficient is-0.94). This research could not only offer some new ideas about qualitatively estimating the crystallinity of quartzite jade by non-destructive testing methods, but also provide some scientific evidence and theoretical restrictions for qualitatively evaluating quartzite jade.

The key parameter to determine whether jadeitite can be named gem grade jadeitite 'jadeite jade' or not is the content (the mass fraction) of jadeite in jadeitite. So far, most methods to determine the mass fraction of mineral in rock are destructive, which is not suitable in gem detection. Based on the changes of mineral composition and mass fraction of mineral in jadeitite, a non-destructive method by measuring the relative density of jadeitite was established in order to get the mass fraction of jadeite. By Static Water Density Method, 186 pieces of jadeitite samples with relative densities of 3.30-3.24 were divided into groups according to different densities. The main mineral composition and mass fraction of minerals in jadeitite were analyzed by X-ray Powder Diffraction, Manual Heavy-sand Analysis, Electron Probe Microanalysis, Infrared Spectrometry and Raman Spectrometry. The linear relationship between the mass fraction of jadeite and the relative density of jadeitite was statisticstically analyzed. Results show that the main minerals in jadeitite are jadeite, albite, and analcite. As the mass fraction (wA) of jadeite decreases, those of albite and analcime increase, and the measured specific gravities (SG) of jadeitite change accordingly. The relationship between them is wA=1.3454 SG-3.4531 (r=0.9814), showing a good linear dependence relation. Because the measured specific gravity of jadeitite is approximately equal to the theoretical one, mass fraction of jadeite is obtained by measuring the specific gravity of jadeitite. This non-destructive method applies to jadeitite with a specific gravity of 3.3-3.0, jadeite content of 95%-60%, and sum mass fractions of jadeite and albite of 90%-97%.

Surface tension is one of the important physical and chemical parameters of the solid surface, which is closely related to temperature and properties of the phases between the boundaries. Based on the Young function, the contact angle measurement method to calculate the solid surface tension has been widely used in surface science and engineering Comparing to other solid materials with inhomogeneous surface, most gemstones have a smooth surface, making it easy to measure the contact angle. In this study, the contact angle of 15 different types of natural and synthetic gemstones including diamond, moissanite, CZ, tourmaline, topaz, jade, amber. And some coated gemstones and fissure filled gemstones have been measured and compared using a dynamic contact angle testing device (FTA200). It was found that the differences in the contact angle for different types of natural and synthetic gemstones are suitable to be used in gemstone identification. For example, contact angle value of diamond and CZ is 56.68° and 37.79°, respectively. Furthermore, the contact angle values between the gemstone and gems with coating process have significant differences, such as the contact angle value of amber is 92.49°, while coated amber is 66.49°. Due to the limitations of the droplet size control restricted by experimental conditions, the contact angle of the fissure-filled gemstones cannot be measured accurately. Herein, this method is not suitable to identify gemstones with artificial fillings. Research shows that contact angle and surface tension values can be used as the basis of supplementary identification of gem species, especially for coated gems. Compared with the conventional gem identification methods (e.g. Infrared Spectrum, the refractive index measurement), contact angle measurement method has higher measuring accuracy, simple operation without destroying the sample, and conforms to the basic principles of gemstone nondestructive identification, especially for high refractive index gem. Contact angle measurement can solve the detection problems for surface-coated gems and related surface property.

Recently, a variety of nephrite with emerald green spots appeared in the nephrite market. There is no report on the mineral composition and green spots for this type of nephrite. Under a higher magnification optical microscope, the complete crystal shape, microstructure and the distribution of the green spots in nephrite were observed. The chemical compositions and mineral phases have been identified using Raman scattering spectrometer and Energy-Dispersive X-ray Fluorescence Spectrometer (ED-XRF) techniques. It was found that the main mineral composition of nephrite is tremolite and the green spots are grossularite. The main coloring element in grossularite is Cr. Therefore, the Cr-bearing grossularite is the main reason for the green spots occurring in the nephrite. It differs from the colouration of traditional green nephrite (jasper) and Qinghai CuiqingYu. The green garnets usually have been observed in jasper, and never found previously in other varieties of nephrite. A certain number of green grossularites with crystal shapes in the nephrite is very important for the study on the origin of this nephrite deposit and the place of its origin.

The geographic locality determination of diamonds is of great significance in understanding the mantle evolution, restricting the illegal trade of conflict diamonds, etc. In the present article, the in-situ analysis of micro-FTIR surface scan technique was first applied to analyze 14 IaAB natural diamond specimens from China's three commercial localities. According to the FTIR spectra of diamonds, the nitrogen contents were calculated (1616 data points of FTIR) and used for mapping tracer. Th results showed that the nitrogen contents and its aggregation often varied in the process of diamond growth, and the nitrogen contents in initial nucleation stage could be higher or lower than in other stages. It is not an unidirectional variation for nitroge contents in different growth stages, indicating that the carbon and nitrogen had a complex exchange with mantle fluid during the diamond's crystallization course. It was regionally different between the diamonds from the three localities in the frequency distribution of nitrogen contents and NB%/N(T). Micro-FTIR mapping is more intuitive than the method of selecting discontinuous points, and it can trace the heterogeneous growth of nitrogen impurities in natural diamonds consecutively.