Gem Crystals

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Mineralogical Crystallography and Biomineralization".

Deadline for manuscript submissions: closed (18 February 2022) | Viewed by 94632

Special Issue Editors


E-Mail Website
Guest Editor
National Gemstone Testing Center, Dongcheng, Beijing, China
Interests: gem identification; gemstone origin, synthesis and treatment
Institute of Geology, Chinese Academy of Geological Sciences, Xicheng District, Beijing, China
Interests: diamond-hosted in ophiolite and kimberlite; gem geology
Special Issues, Collections and Topics in MDPI journals

E-Mail Website
Guest Editor
1. Gemological Institute of America, 50 W 47th St, New York, NY 10036, USA
2. EAPS, 550 Stadium Mall Drive, West Lafayette, IN 47907, USA
Interests: diamonds and color stones; mineral and rock physics; theoretical simulations; geochemistry

Special Issue Information

Dear Colleagues,

We are pleased to announce the forthcoming “International Gems & Jewelry Academic Conference” organized by the National Gemstone Testing Center (NGTC), China, which will be held in Beijing on November 2021, and to invite you to contribute to the present joint Special Issue of Crystals entitled “Gem Crystals”.

Gem crystals, the most fascinating treasures conceived by our mother Earth under extremely high temperatures and pressurized deep regions or through biological procedures, possess the three essential virtues of rarity, durability, and beauty. Not only do gem crystals provide information on culture and human history before language was written, they also shed light on the hidden story of our planet in a way recorded by their crystal structures, defects, textures, morphologies, chemistry, etc. Inclusions in gem crystals play a critical role in the Earth sciences, which unveil the forming conditions of their host stones and inform on the inner working of Earth’s interior. Simulations of the natural conditions not only gave birth to the synthetic gemstones, they have also been applied to renovate the appearances of both natural and synthetic gems for aesthetic reasons. Their chemical and physical properties are essential to gemologists in developing criteria for impartial evaluation and identification, which are the cornerstones of the gem industry.

We invite researchers to contribute to this Special Issue on Gem Crystals, which is intended to serve as a unique multidisciplinary forum covering broad aspects of the science, technology, and application of gemstones.

The potential topics include, but are not limited to:

  • Genesis of inorganic and organic gems;
  • Synthesis and treatment of gemstones;
  • Structures and defects of synthetic and natural gemstones;
  • Gemstone morphology and texture;
  • Characterization and identification of gemstones by advanced techniques;
  • Geological messages unlocked by gemstones through their inclusions or physical properties.

The submission of original research papers or reviews to this Special Issue of Crystals is open for both participants of the conference and other researchers working in the field of gem crystals.

Dr. Taijin Lu
Dr. Fei Liu
Dr. Tingting Gu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Diamonds and color stones
  • Gem synthesis and treatment
  • Defects
  • Characterization
  • Identification
  • High pressure/high temperature
  • Inclusions

Published Papers (32 papers)

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Research

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12 pages, 3195 KiB  
Article
Gemological Characteristics and Chemical Composition of a New Type of Black Jadeite and Three Imitations
by Beiqi Zheng, Ke Li and Yuyang Zhang
Crystals 2022, 12(5), 658; https://doi.org/10.3390/cryst12050658 - 4 May 2022
Cited by 1 | Viewed by 2102
Abstract
Because of the increasing price of jadeite, many fake species have appeared on the market. We recognized three pieces of fake black jadeite that had been placed among real black jadeite. In this study we conducted a mineralogical investigation of the three fakes [...] Read more.
Because of the increasing price of jadeite, many fake species have appeared on the market. We recognized three pieces of fake black jadeite that had been placed among real black jadeite. In this study we conducted a mineralogical investigation of the three fakes and the real jadeite by using FTIR and XRD techniques; in addition, we performed in situ major, minor and trace element chemical characterization based on EPMA-WDS and LA-ICP-MS techniques. The three imitations have different components, dominated by katophorite (97%), augite (66%) and anorthite (97%). In contrast, the real jadeite sample contains more than 99% jadeite. Unlike previous reports on black jadeite, the dark omphacite exsolution around the jadeite cleavage is the chromogenic factor in the present study, whereas the black color of the imitations comes from light absorption by major melanocratic minerals and widespread fine graphite. We propose that 2–4 sharp bands between 600 and 800 cm−1 of FTIR and the 2.42 and 2.49 Å peaks of XRD can be used to discriminate black jadeite from imitations. Even though natural jadeite deposits are being exhausted, materials of the three natural imitations were determined not to be suitable for jewelry due to low hardness, widespread occurrence and unknown injury of the radioactive elements thorium and uranium. Otherwise, they could enhance value and be ideal for large-sized ornaments of fine design. Full article
(This article belongs to the Special Issue Gem Crystals)
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14 pages, 4787 KiB  
Article
Gemology, Mineralogy, and Coloration Mechanism of Pinkish-Purple Cobaltoan Dolomite from the Democratic Republic of Congo
by Ying Yan and Xiao-Yan Yu
Crystals 2022, 12(5), 639; https://doi.org/10.3390/cryst12050639 - 29 Apr 2022
Cited by 1 | Viewed by 2278
Abstract
A pinkish-purple cobaltoan dolomite from the Democratic Republic of Congo (DRC) has appeared on the Chinese gemstone market recently. In this study, Raman analysis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, electron probe micro-analysis (EPMA), scanning electron microscopy (SEM), energy-dispersive X-ray fluorescence (EDXRF), and [...] Read more.
A pinkish-purple cobaltoan dolomite from the Democratic Republic of Congo (DRC) has appeared on the Chinese gemstone market recently. In this study, Raman analysis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, electron probe micro-analysis (EPMA), scanning electron microscopy (SEM), energy-dispersive X-ray fluorescence (EDXRF), and fiber optic spectrometry were used to explore the gemology, mineralogy, and coloration mechanism of cobaltoan dolomite. Results indicate that cobaltoan dolomite is a mineral aggregate with a granular texture. The degree of fineness and luster differs due to mineral (quartz) impurities in the texture. The cobaltoan dolomites are typically associated with carbonates, such as azurite, malachite, spherocobaltite, and the rare species kolwezite, which were documented in this study. The natural presence of magnesite-spherocobaltite solid solution with distinct chemical zoning occurs as crystals in the country rock. The pinkish-purple dolomites are mainly colored by CoO, whose concentrations ranged from 0.966 to 6.111 wt.%. Based on UV-Vis spectroscopy, cobaltoan dolomite showed broad characteristic absorption bands at 531.5 nm, which varied as the concentrations of CoO increased. The origin of the color is related to the electronic transition of Co2+ and charge transfer between the ions. Full article
(This article belongs to the Special Issue Gem Crystals)
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14 pages, 5169 KiB  
Article
A Comparative Study of the Gemological Characteristics and Inclusions in Spinels from Myanmar and Tajikistan
by Yi Zhang, Jing-Ran Zhu and Xiao-Yan Yu
Crystals 2022, 12(5), 617; https://doi.org/10.3390/cryst12050617 - 27 Apr 2022
Cited by 3 | Viewed by 2512
Abstract
Currently, most of the popular spinels in the jewellery market come from Myanmar and Tajikistan. It is well known that provenance is one of the main factors affecting the value of a gemstone, and the geographic origin of a gemstone can be determined [...] Read more.
Currently, most of the popular spinels in the jewellery market come from Myanmar and Tajikistan. It is well known that provenance is one of the main factors affecting the value of a gemstone, and the geographic origin of a gemstone can be determined by examining its gemological and inclusion characteristics. This study systematically characterized the conventional gemology of spinels from Myanmar and Tajikistan and compared the inclusions in the spinels from these two countries by means of gemological microscopy and Raman spectroscopy. The results showed that most red and pink Myanmarese spinels were octahedral or contact twins, while Tajikistani spinels are slabbed or octahedral distorted crystals. Columnar zircon is frequently found in Tajikistani spinels but rare in Myanmarese spinels, appearing as tiny accessory inclusions. There are three types of carbonate inclusions (magnesite, dolomite, and calcite) in Myanmarese spinels, but Tajikistani spinels have only one (magnesite). In addition, spinels of different origins include special inclusions. Myanmarese spinels contain pyrite inclusions; Tajikistani spinels contain rutile and talc inclusions. Full article
(This article belongs to the Special Issue Gem Crystals)
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13 pages, 2102 KiB  
Article
Mineralogy and Geochemistry of JingFenCui (Rhodonite Jade) Deposit from Beijing, China
by Zhi-Juan Kang, Guang-Hai Shi, Wei-Yan Lei, Cai-Xiu An, Lu Liu, Shu-Hong Liu, Feng Lu and Lin Xu
Crystals 2022, 12(4), 483; https://doi.org/10.3390/cryst12040483 - 31 Mar 2022
Viewed by 1882
Abstract
JingFenCui is a type of rhodonite jade from the Changping district of Beijing, China, which is a manganese skarn deposit formed through the metasomatism of the granite aplite and Cambrian limestone. The pink color of JingFenCui is richer and brighter than that of [...] Read more.
JingFenCui is a type of rhodonite jade from the Changping district of Beijing, China, which is a manganese skarn deposit formed through the metasomatism of the granite aplite and Cambrian limestone. The pink color of JingFenCui is richer and brighter than that of rhodonite jade from other deposits. The surface of JingFenCui exhibits dendritic iron and manganese oxides, which is the outstanding advantage of rhodonite jade for carving works. The zoning pattern of mineralogy between the contact zone with the wallrock is obvious. The main skarn minerals consist mainly of spessartine, diopside, augite, manganotremolite, clino-suenoite, rhodonite, galena, etc. Compared with rhodonite jade from the Makeng in Fujian and the Luziyuan in western Yunnan, vittinkiite (MnSiO3) is more concentrated in the rhodonite of the JingFenCui Deposit as a Mn-Ag-Pb-Zn-Fe polymetallic deposit. There is a good agreement among the rhodonite, amphibole, and galena in the spider diagrams of the trace elements. The results of trace elements and REE analysis show that the metallogenic fluids of the JingFenCui deposit are mainly from magma related to the Heixiongshan granite. It is suggested that the JingFenCui deposit is a manganese skarn deposit formed through the metasomatism of the manganese-bearing limestone and fine-grained granite of the Heixiongshan. Full article
(This article belongs to the Special Issue Gem Crystals)
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13 pages, 2821 KiB  
Article
Color Genesis and Compositional Characteristics of Color-Change Sapphire from Fuping, China
by Hui Wang, Xiao-Yan Yu, Fei Liu, Masroor Alam and Gai-Chao Wu
Crystals 2022, 12(4), 463; https://doi.org/10.3390/cryst12040463 - 27 Mar 2022
Cited by 3 | Viewed by 2057
Abstract
The color-change sapphire occurs in sillimanite-biotite gneiss in Fuping County Hebei province, China, is one of most famous sapphire deposits in China. However, the color genesis, mechanisms of color changing and compositional characteristics of the sapphire remain enigmatic. In this contribution, the coloration [...] Read more.
The color-change sapphire occurs in sillimanite-biotite gneiss in Fuping County Hebei province, China, is one of most famous sapphire deposits in China. However, the color genesis, mechanisms of color changing and compositional characteristics of the sapphire remain enigmatic. In this contribution, the coloration in the Fuping sapphire, color changing mechanisms and, compositional characteristics were studied by conventional gemological instruments in conjunction with ultraviolet-visible spectroscopy and Laser ablation inductively coupled plasma mass spectrometer. The results show that the Fuping sapphire is characterized by purple-blue-to-purple-red changed effect and column-shaped, waist drum-shaped with higher degree of euhedral crystal. Reddish brown rutile inclusions with 120° crossed cleavage are commonly observed. The dominant coloring element of the Fuping sapphire is Fe3+, and subordinate elements are Fe2+, Cr3+ and V3+. The color-change effect is caused by trace elements Cr3+ and V3+. The chemical compositions of Fuping color-change sapphires are analogous to those of metamorphic blue sapphires. When geochemically compared with sapphires from Isalo/Ilakaka deposit in Madagascar, Ratnapura deposit in Sri Lanka and Mogok in Myanmar, the Fuping color-change sapphires have distinctly higher rare element contents of Fe, Cr and Ga. Full article
(This article belongs to the Special Issue Gem Crystals)
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21 pages, 3861 KiB  
Article
A Study on Apatite from Mesozoic Alkaline Intrusive Complexes, Central High Atlas, Morocco
by Pengyu Yuan, Bo Xu, Zixuan Wang and Daiyue Liu
Crystals 2022, 12(4), 461; https://doi.org/10.3390/cryst12040461 - 25 Mar 2022
Cited by 6 | Viewed by 2218
Abstract
There are abundant phosphate mines in the High Atlas Mountains of Morocco. Gem-quality apatite is produced at the Anemzi deposit, but its associated gem mineralogy is relatively poorly studied. In this study, apatite from the Anemzi mine in Morocco was analysed using standard [...] Read more.
There are abundant phosphate mines in the High Atlas Mountains of Morocco. Gem-quality apatite is produced at the Anemzi deposit, but its associated gem mineralogy is relatively poorly studied. In this study, apatite from the Anemzi mine in Morocco was analysed using standard gemmological characterisation methods, including basic tests (hardness, relative density, microscopy, etc.), spectroscopic tests (infrared, Raman, and ultraviolet–visible spectroscopy), and chemical analyses (electron probe and laser ablation inductively coupled plasma mass spectrometry). This paper explores the gemmological characteristics of Moroccan apatites and the information on diagenesis recorded for apatites by comparing them with apatites from other sources. Apatite from the Anemzi deposit is an igneous fluorapatite. The relatively high Cl content of the apatite suggests that the magma in the area has a high Cl content, whereas the high Cl/F ratio may indicate that the deposit formed in a slab subduction environment. The characteristics of the major and trace elements indicate high oxygen and sulphur escapes in the apatite-forming magma. Full article
(This article belongs to the Special Issue Gem Crystals)
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22 pages, 4036 KiB  
Article
Color Genesis of Brown Diamond from the Mengyin Kimberlite, China
by Gai-Chao Wu, Xiao-Yan Yu, Fei Liu, Hai-Bo Li, Zheng-Yu Long and Hui Wang
Crystals 2022, 12(4), 449; https://doi.org/10.3390/cryst12040449 - 23 Mar 2022
Cited by 5 | Viewed by 2337
Abstract
The Mengyin diamondiferous kimberlite cluster in Shandong province is one of the three major sources of natural diamond in China, where many brown diamonds are mined, but the genesis of their color is still controversial. In this paper, studies including microscopic examination, optical [...] Read more.
The Mengyin diamondiferous kimberlite cluster in Shandong province is one of the three major sources of natural diamond in China, where many brown diamonds are mined, but the genesis of their color is still controversial. In this paper, studies including microscopic examination, optical properties of orthogonal polarization, low temperature photoluminescence spectra, infrared spectra, Raman spectra, ultraviolet-visible absorption spectra, luminescence of cathodoluminescence, and transmission electron microscopy have been carried out on the uncut brown diamonds and their slice samples to constrain on the color genesis of brown diamond from the Mengyin deposit. The results show that the brown color is dominantly caused by plastic deformation, and some samples are also caused by non-deformation-related defects and inclusions. Full article
(This article belongs to the Special Issue Gem Crystals)
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11 pages, 2172 KiB  
Article
New Insights into Coloration Mechanism in Violet-Red Pyrope-Almandine
by Puyue Yang and Ying Guo
Crystals 2022, 12(3), 379; https://doi.org/10.3390/cryst12030379 - 11 Mar 2022
Cited by 4 | Viewed by 2262
Abstract
The most common type of garnet is pyrope-almandine, whose color varies from red to violet. In this study, 36 faceted gem-quality samples are used for electron microprobe, infrared spectrum, and UV-Visible spectrum test to find the coloration mechanism and spectroscopic characters in red-violet [...] Read more.
The most common type of garnet is pyrope-almandine, whose color varies from red to violet. In this study, 36 faceted gem-quality samples are used for electron microprobe, infrared spectrum, and UV-Visible spectrum test to find the coloration mechanism and spectroscopic characters in red-violet pyrope-almandine. The gradually increasing content of Mg2+ at the X position in the lattice is connected to the variation in the infrared spectrum. The wavenumber increases with the decrease of cationic radius, which makes the distance between C and D bands further. The color mechanism is mainly affected by Fe2+, and Mn2+. We discuss the change in colors with the assumption of a certain MnO content. When it is above or below the standard of 1 wt%, the absorption intensity of the UV-Visible spectrum is completely different in the purple zone, which determines the color to be red or violet. Therefore, the effect of Mn2+ and Fe2+ should be combined instead of being considered respectively. The results show that the MnO content can be quickly inferred by the light purple/fancy purple color. To avoid harming the value, this new insight makes it possible to quickly classify the gem quality in mining as well as in the market. Full article
(This article belongs to the Special Issue Gem Crystals)
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17 pages, 4456 KiB  
Article
Water Molecules in Channels of Natural Emeralds from Dayakou (China) and Colombia: Spectroscopic, Chemical and Crystal Structural Investigations
by Yu-Yu Zheng, Xiao-Yan Yu, Bo Xu, Ting-Ya Zhang, Ming-Ke Wu, Jia-Xin Wan, Hong-Shu Guo, Zheng-Yu Long, Lin-Yan Chen and Li-Jie Qin
Crystals 2022, 12(3), 331; https://doi.org/10.3390/cryst12030331 - 27 Feb 2022
Cited by 3 | Viewed by 2298
Abstract
H2O molecules in emerald channels have been extensively discussed over the past half century. Recent studies paid attention to their classification and coordination, but have mostly focused on the type related to Na+. There are few works on the [...] Read more.
H2O molecules in emerald channels have been extensively discussed over the past half century. Recent studies paid attention to their classification and coordination, but have mostly focused on the type related to Na+. There are few works on the other types, and the related infrared (IR) absorption bands are rather controversial. This paper investigated natural emeralds from China and Colombia by means of micro-Fourier transform infrared (μ-FTIR) spectroscopy, micro-confocal Raman spectroscopy, and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). The results suggested that doubly (IId) and singly (IIs) coordinated H2O molecules were incorporated in natural emerald channels. Type IId H2O predominated in those emeralds with relatively low alkali content. As the alkali content increased, the proportion of type IIs H2O rose, stemming from the decrease of the H2OII/Na+ apfu ratio. Moreover, IR bands of H2O corresponding to Li+ and Cs+ were tentatively ascribed here. IR bands for D2O and HDO in Colombian sample were observed in the range of 2600–2850 cm−1 and preliminarily assigned, which might be a potential tool for emerald origin determination. Our work expanded the existing classification of water molecules in emerald channels and redefined the controversial IR absorption bands. Full article
(This article belongs to the Special Issue Gem Crystals)
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15 pages, 5676 KiB  
Article
Comparison of Natural and Dyed Fire Opal
by Jinlin Wu, Hong Ma, Ying Ma, Peiying Ning, Na Tang and Huihuang Li
Crystals 2022, 12(3), 322; https://doi.org/10.3390/cryst12030322 - 25 Feb 2022
Cited by 2 | Viewed by 4571
Abstract
Fire opal is much sought after for its flame-like red-orange-yellow body-color. With consumers’ enthusiasm for fire opals, dyed fire opal has gradually entered the jewelry market, which has made an impact on consumer perception and trade. In this work, we present a combined [...] Read more.
Fire opal is much sought after for its flame-like red-orange-yellow body-color. With consumers’ enthusiasm for fire opals, dyed fire opal has gradually entered the jewelry market, which has made an impact on consumer perception and trade. In this work, we present a combined spectroscopic (FTIR, Raman, UV-Vis) investigation and chemical analysis of four natural fire opals from Mexico and Ethiopia and four dyed samples. Ultra-depth microphotographs revealed uniform color distribution in the natural fire opal, while patches of color were observed in the dyed fire opal. The main infrared peak around 1099 cm−1 indicated the hydrophane origin of all the dyed materials. The color of natural fire opals is related to the presence of Fe oxides and hydroxides (hematite, goethite) as confirmed by the Raman spectra, the first derivative of the UV-Vis spectral curves, and the relatively high Fe content by chemical analysis. By contrast, dyeing opals created several Raman peaks produced by external materials, and an extremely low Fe content was detected. The first derivative of the UV-Vis spectral curves can aid in detecting the use of a dyeing treatment in red and yellow opal. Full article
(This article belongs to the Special Issue Gem Crystals)
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13 pages, 16231 KiB  
Article
Identification of Heat-Treated Sapphires from Sri Lanka: Evidence from Three-Dimensional Fluorescence Spectroscopy
by Yuyang Zhang and Meihua Chen
Crystals 2022, 12(2), 293; https://doi.org/10.3390/cryst12020293 - 19 Feb 2022
Viewed by 3811
Abstract
Heat treatment is an important method used to improve the value of sapphires. The identification of heat-treated sapphires is a significant and challenging subject in gemology. In this study, natural sapphire samples from Ratnapura, Sri Lanka, were heated at different temperatures from 900 [...] Read more.
Heat treatment is an important method used to improve the value of sapphires. The identification of heat-treated sapphires is a significant and challenging subject in gemology. In this study, natural sapphire samples from Ratnapura, Sri Lanka, were heated at different temperatures from 900 °C to 1500 °C. Then, the samples were examined by FTIR and three-dimensional fluorescence spectrometry. When excited by 450 nm light, most natural samples emitted a fluorescence band between 540 nm and 560 nm. This fluorescence disappeared after low-temperature heat treatment. Therefore, the presence of fluorescence between 540 nm and 560 nm is evidence of unheated sapphires from Sri Lanka. Almost all of the samples emitted fluorescence centered at 470 nm after high-temperature treatment. Therefore, fluorescence at 470 nm indicates that the sapphires from Sri Lanka were treated at a high temperature. Three-dimensional fluorescence spectroscopy can serve as a method to identify heat-treated sapphires. Full article
(This article belongs to the Special Issue Gem Crystals)
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20 pages, 8538 KiB  
Article
Mineralogy and Geochemistry of “Laoshan Jade” from Shandong Province, China: Implications for Petrogenesis
by Xiaomin Yu, Yingxin Liu and Chuqi Cao
Crystals 2022, 12(2), 243; https://doi.org/10.3390/cryst12020243 - 11 Feb 2022
Cited by 1 | Viewed by 1749
Abstract
“Laoshan Jade” is located in the Yangkou area of the Sulu UHP metamorphic belt. This is the first time a systematic research study is performed on its conventional gemological characteristics, mineral compositions, geochemical characteristics, and petrogenesis using a polarized light microscope, an electron [...] Read more.
“Laoshan Jade” is located in the Yangkou area of the Sulu UHP metamorphic belt. This is the first time a systematic research study is performed on its conventional gemological characteristics, mineral compositions, geochemical characteristics, and petrogenesis using a polarized light microscope, an electron probe microanalyzer (EMPA), an X-ray fluorescence spectrometer (XRF), and a Raman spectrometer. The gemological characteristics of “Laoshan Jade” are consistent with serpentine jade. It can be named serpentinite, mainly composed of serpentine (antigorite), chlorite (clinochlore), and magnetite. Some samples contain magnesite and chromite. Only small amounts of unaltered forsterite, chrysolite, and diopside can be found in poor-quality serpentine jade. The protolith of “Laoshan Jade” is metamorphic peridotite. Antigorite is altered from olivine. Clinochlorite is altered from the diopside. Disseminated magnetite is the metamorphic product. Unaltered olivine and diopside belong to protolith. Chromite with zonal texture also belongs to protolith. The average temperature and pressure of its core are calculated to be 1348 °C and 3.1 GPa, which indicates that the protolith comes from the mantle asthenosphere. The formation temperature of its edge is lower than 500 °C, with metamorphic origin. XRF experiments show that “Laoshan Jade” samples are relatively rich in Mg and more depleted in fusible elements (Al, Ca) than the original mantle peridotite, indicating that serpentinite protolith has undergone a certain degree of partial melting. Combined with EPMA results, the findings of this study reveal that protolith belongs to the depleted mantle peridotite in the subduction zone, partially melted in the mantle wedge, and reacted with subduction zone fluid. Pyroxene is altered into chlorite, olivine is altered into serpentine, and magnet is generated. The edge of chromite in the protolith is altered by the iron-rich fluid into magnetite. Finally, serpentinite is formed. Full article
(This article belongs to the Special Issue Gem Crystals)
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13 pages, 4713 KiB  
Article
The Effect of Munsell Neutral Value Scale on the Color of Yellow Jadeite and Comparison between AP and K-Means Clustering Color Grading Schemes
by Ziyuan Liu and Ying Guo
Crystals 2022, 12(2), 241; https://doi.org/10.3390/cryst12020241 - 10 Feb 2022
Cited by 11 | Viewed by 2181
Abstract
Yellow jadeite is a kind of jadeite caused by secondary leaches. With a certain degree of transparency, its color is usually influenced by the objective conditions including light source and background. In this paper, 19 Munsell neutral value scales were selected to study [...] Read more.
Yellow jadeite is a kind of jadeite caused by secondary leaches. With a certain degree of transparency, its color is usually influenced by the objective conditions including light source and background. In this paper, 19 Munsell neutral value scales were selected to study the impact caused by background under the standard light source D65, where we found that the N9.5 Value Scale is suitable for color grading. All 33 yellow jadeites were tested by UV-VIS spectrophotometer and colorimetric analysis, and the colors were graded by the affinity propagation (AP) and K-means clustering methods. According to the result, the yellow jadeite color was classified into Fancy, Fancy Intense, Fancy Deep, and Fancy Light. It is also concluded that AP is more feasible to provide the color grading scheme, while K-means can be applied to the optimization of choosing clustering center. Full article
(This article belongs to the Special Issue Gem Crystals)
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6 pages, 1637 KiB  
Article
Study on the Influence of Porosity of the Nacre Layer on the Luster and Surface Roughness of Chinese Large Freshwater Nucleated Pearl
by Danyi Zhou, Taijin Lu, Ruoduan Sun and Jian Zhang
Crystals 2022, 12(2), 234; https://doi.org/10.3390/cryst12020234 - 9 Feb 2022
Viewed by 1618
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Gem Crystals)
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13 pages, 3739 KiB  
Article
The Chemical Composition of Trapiche-like Quartz from Huanggangliang Area, Inner Mongolia, China
by Ling Jiang, Zhu Chen and Yingxin Liu
Crystals 2022, 12(1), 122; https://doi.org/10.3390/cryst12010122 - 17 Jan 2022
Cited by 2 | Viewed by 2064
Abstract
Trapiche-like quartz, which is found in Huanggangliang area, Chifeng City, Inner Mongolia, China, has a short columnar euhedral shape. Arms of trapiche-like phenomena are formed by six radial dark bands located along the a-axis of crystals, and their cores are formed by [...] Read more.
Trapiche-like quartz, which is found in Huanggangliang area, Chifeng City, Inner Mongolia, China, has a short columnar euhedral shape. Arms of trapiche-like phenomena are formed by six radial dark bands located along the a-axis of crystals, and their cores are formed by color zones. Various methods were used to investigate the conventional gemological characteristics, trapiche pattern features, chemical compositions, and spectral characteristics of the trapiche-like quartz. CL images and EPMA results reveal they were formed at high temperature conditions and originated from pegmatite. The hexagonal darker zones with high FeO and very little TiO2 contents indicate the trapiche-like patterns are due to spatial distribution of color-inducing elements. According to the position and interpenetration relationship between inclusions, fibrous and spherical inclusions are identified as protogenetic inclusions, which were respectively identified to be ferro-actinolite and iron oxide by EPMA and Raman spectra. Full article
(This article belongs to the Special Issue Gem Crystals)
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16 pages, 3521 KiB  
Article
Correlations between Garnet Species and Vibration Spectroscopy: Isomorphous Substitution Implications
by Weiwei Li, Jinyu Zheng, Jingcheng Pei, Xing Xu and Tao Chen
Crystals 2022, 12(1), 104; https://doi.org/10.3390/cryst12010104 - 13 Jan 2022
Cited by 7 | Viewed by 4909
Abstract
Garnet has many species because of its common isomorphism. In this study, a suite of 25 natural gem-quality garnets, including pyrope, almandine, spessartine, grossular, and andradite, were examined by standard gemological testing, LA-ICP-MS, FTIR, and Raman analysis. Internal stretching and bending vibrations of [...] Read more.
Garnet has many species because of its common isomorphism. In this study, a suite of 25 natural gem-quality garnets, including pyrope, almandine, spessartine, grossular, and andradite, were examined by standard gemological testing, LA-ICP-MS, FTIR, and Raman analysis. Internal stretching and bending vibrations of the SiO4-tetrahedra of garnet exhibit correlate with the type of cations in garnet’s dodecahedral position (A site) and octahedral position (B site). FTIR and Raman spectra showed that with the increase of the radius of Mg2+, Fe2+, Mn2+, and Ca2+ in A site, or the unit cell volumes of pyrope, almandine, spessartine, and grossular, the spectral peaks of Si–Ostr and Si–Obend modes shift to low wavenumber. Because of the largest cations both in A site (Ca2+) and in B site (Fe3+), andradite exhibited the lowest wavenumber of Si–Ostr and Si–Obend modes of the five garnet species. Therefore, garnet has correlations between chemical composition and vibration spectroscopy, and Raman or IR spectroscopy can be used to precisely identify garnet species. Full article
(This article belongs to the Special Issue Gem Crystals)
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15 pages, 6306 KiB  
Article
Gem Elbaite as a Recorder of Pegmatite Evolution: In Situ Major, Trace Elements and Boron Isotope Analysis of a Colour-Zoning Tourmaline Crystal
by Beiqi Zheng and Meihua Chen
Crystals 2021, 11(11), 1363; https://doi.org/10.3390/cryst11111363 - 8 Nov 2021
Cited by 2 | Viewed by 1693
Abstract
Few studies have focused on gem-quality tourmaline acting as a petrogenetic recorder, and the colour genesis of pink elbaite is still controversial. We carry out in situ major, trace element and boron isotope composition analyses on a single tourmaline crystal. This crystal is [...] Read more.
Few studies have focused on gem-quality tourmaline acting as a petrogenetic recorder, and the colour genesis of pink elbaite is still controversial. We carry out in situ major, trace element and boron isotope composition analyses on a single tourmaline crystal. This crystal is characterized by sudden transformation from colourless to pink, which can represent full pegmatite magma evolution. According to the analysis results, all spots are divided into alkali groups according to X-site occupancy and subdivided into elbaite series. The pink part accommodates higher concentrations of volatile and incompatible elements. The result is most consistent with successive pegmatite evolution in which the colourless part crystallized from the early stage, while the pink part crystallized from the late stage. The relatively consistent δ11B value between the colourless and the pink part suggests no fluid exsolution occurred during pegmatite evolution. The slight increase of δ11B values within the pink part and the colourless part may be due to mica crystallization. The combination of (Li++Mn2+) (Al3++Xvac)-1 and the exclusive positive linear relationship of Mn2+ vs. Ti4+ indicate that Mn2+ is the main cause of pink, while Mn2+-Ti4+ intervalence charge transfer also plays an important role. Full article
(This article belongs to the Special Issue Gem Crystals)
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11 pages, 2383 KiB  
Article
Microdiamonds in Alkalic Dolerites from the North China Craton: FTIR and C Isotopic Characteristics
by Yitao Cai, Zhengqi Cao, Fei Liu, Kan Li, Long Li and Jingsui Yang
Crystals 2021, 11(11), 1325; https://doi.org/10.3390/cryst11111325 - 29 Oct 2021
Viewed by 1635
Abstract
Most of the diamond deposits in China are in the North China Craton. In addition to gem diamonds in kimberlite, a large number of microdiamonds have also been discovered in alkaline dolerites. These microdiamonds show very different characteristics from those recovered in kimberlite. [...] Read more.
Most of the diamond deposits in China are in the North China Craton. In addition to gem diamonds in kimberlite, a large number of microdiamonds have also been discovered in alkaline dolerites. These microdiamonds show very different characteristics from those recovered in kimberlite. Here, we report the morphology, colour, nitrogen contents, and carbon isotopic compositions of the diamonds recovered from the alkalic dolerites in eastern China. The microdiamonds are mainly cube and rhombic dodecahedron with diameters of 0.2 to 0.6 mm. Infrared spectrum analysis shows that these microdiamonds are mostly type Ib with a small amount of type Ia. The Y centre is obvious in type Ib diamond. Modelling mantle residence times for the IaAB diamonds is about 550 Ma. Nitrogen contents of the diamonds range from 4.5–503 ppm, with a median value of 173 ppm. The total δ13C range of the microdiamonds varies between −18.6 and −21.1‰ and are similar to those of ophiolite diamond. Full article
(This article belongs to the Special Issue Gem Crystals)
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12 pages, 3067 KiB  
Article
Beryl Reference Materials for In Situ Oxygen Isotope Determination
by Xiaoxiao Ling, Qiuli Li, Lianjun Feng, Di Zhang, Yu Liu, Guoqiang Tang, Jiao Li, Shitou Wu, Liangliang Huang, Tiejun Li, Yan Liu, Ronald Werner and Xianhua Li
Crystals 2021, 11(11), 1322; https://doi.org/10.3390/cryst11111322 - 29 Oct 2021
Cited by 2 | Viewed by 1796
Abstract
The mineral beryl (Be3Al2(SiO3)6) has the most abundant phase with industrial value for extracting a critical metal—beryllium. Due to multi-stage, fluid-induced growth, individual beryl grains may yield complex geochemical records, revealing variations in the oxygen [...] Read more.
The mineral beryl (Be3Al2(SiO3)6) has the most abundant phase with industrial value for extracting a critical metal—beryllium. Due to multi-stage, fluid-induced growth, individual beryl grains may yield complex geochemical records, revealing variations in the oxygen isotopes of the fluids from which they crystallize. Secondary ion mass spectrometry (SIMS) with high sensitivity and high spatial resolution represents a good tool for in situ isotopic analysis. SIMS oxygen analyses require matrix-matched reference materials to calibrate instrumental mass fractionations during measurement. In this work, the oxygen isotope homogeneities of six beryl samples with different compositions (BS1, BS2, BS3, BS4, BS5, and BS6) were documented by SIMS. These samples’ recommended oxygen isotope compositions were characterized by laser fluorination isotope ratio mass spectrometry (IRMS). This study suggests that there is no matrix effect related to composition variation in beryl SIMS oxygen isotope analysis. The recommended δ18O values of the four reference materials, BS1, BS2, BS4, and BS5, were 15.01 ± 0.34‰ (2 standard deviations, 2 SD), 7.53 ± 0.16‰ (2 SD), 2.38 ± 0.14‰ (2 SD), and 10.72 ± 0.44‰ (2 SD), respectively. Therefore, BS1, BS2, BS4, and BS5 are recommended as suitable reference materials for in situ mineral beryl oxygen isotope microanalysis. Full article
(This article belongs to the Special Issue Gem Crystals)
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9 pages, 5691 KiB  
Article
Discovery of Disulfane (H2S2) in Fluid Inclusions in Rubies from Yuanjiang, China, and Its Implications
by Wenqing Huang, Pei Ni, Jungui Zhou, Ting Shui, Junying Ding, Renzhi Zhu, Yitao Cai and Mingsen Fan
Crystals 2021, 11(11), 1305; https://doi.org/10.3390/cryst11111305 - 27 Oct 2021
Cited by 1 | Viewed by 1405
Abstract
Raman spectra of fluid inclusions in gem rubies from Yuanjiang deposit (China) within the Ailao Shan-Red River (ASRR) metamorphic belt showed the presence of compounds such as CO2, COS, CH4, H2S, and elemental sulfur (S8), [...] Read more.
Raman spectra of fluid inclusions in gem rubies from Yuanjiang deposit (China) within the Ailao Shan-Red River (ASRR) metamorphic belt showed the presence of compounds such as CO2, COS, CH4, H2S, and elemental sulfur (S8), accompanied by two bands at approximately 2499 and 2570 cm−1. These two frequencies could be assigned to the vibrations of disulfane (H2S2). This is the second case of the sulfane-bearing fluid inclusions in geological samples reported, followed by the first in quartzite from Bastar Craton of India. The H2S2 was likely in situ enclosed by the host rubies rather than a reaction product that formed during the cooling of H2S and S8, suggesting sulfanes are stable at elevated temperatures (e.g., >600 °C). By comparing the lithologies and metamorphic conditions of these two sulfane-bearing cases (Bastar and Yuanjiang), it is suggested that amphibolite facies metamorphism of sedimentary sequence that deposited in a continental platform setting might favor the generation of sulfanes. Sulfanes may play an important role in the mobilization of Cr that is essential for ruby crystallization. Full article
(This article belongs to the Special Issue Gem Crystals)
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14 pages, 44266 KiB  
Article
The Different Inclusions’ Characteristics between Natural and Heat-Treated Tanzanite: Evidence from Raman Spectroscopy
by Shuqi Yang, Huijuan Ye and Yingxin Liu
Crystals 2021, 11(11), 1302; https://doi.org/10.3390/cryst11111302 - 26 Oct 2021
Cited by 3 | Viewed by 2810
Abstract
In this paper, Raman spectroscopy experiments were used to distinguish the characteristics of inclusions (calcite, anatase, graphite etc.) between natural and heat-treated tanzanite. These characteristics were preliminarily divided according to their pleochroism. In natural unheated tanzanite (N5), calcite inclusion is often interspersed with [...] Read more.
In this paper, Raman spectroscopy experiments were used to distinguish the characteristics of inclusions (calcite, anatase, graphite etc.) between natural and heat-treated tanzanite. These characteristics were preliminarily divided according to their pleochroism. In natural unheated tanzanite (N5), calcite inclusion is often interspersed with dolomite and has Raman shifts around 156, 283, 710, and 1087 cm−1. In other high temperature treatment samples, the baseline of calcite increased and their Raman peaks gradually shifted towards lower frequencies. Anatase inclusions in natural tanzanite (N5) have four characteristic Raman peaks around 146, 394, 514, and 641 cm−1. Because of the longer Ti-O bond and the wider bond angle distribution caused by high temperature, fewer Raman peaks were observed and the peaks’ intensities were weakened in the heat-treated T7 sample. The black graphite inclusions are often scattered or have a dotted distribution. The most obvious difference between natural and heat-treated samples is that the latter lack the characteristic 1350 cm−1 Raman peak of graphite, thus representing the order and structural incompleteness of graphite. In addition, there are other inclusions in natural unheated tanzanite, such as lead-grey molybdenite with strong metallic luster, randomly scattered prehnite with white dots, orange-yellow rounded rutile, and metallic luster hematite. Full article
(This article belongs to the Special Issue Gem Crystals)
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12 pages, 10883 KiB  
Article
In-Situ Infrared Spectra of OH in Pakistan Forsterite at High Temperature
by Xiao-Guang Li, Wen Su, Yu-Yu Zheng and Xiao-Yan Yu
Crystals 2021, 11(11), 1277; https://doi.org/10.3390/cryst11111277 - 21 Oct 2021
Cited by 1 | Viewed by 1443
Abstract
The hydroxyl of the gem-grade forsterite from Pakistan was measured by the polarized spectra at room temperature to 1000 °C, showing four unambiguous absorption bands at 3612, 3597, 3579, and 3566 cm−1. Here, we report angle-resolved polarized IR spectroscopy of the [...] Read more.
The hydroxyl of the gem-grade forsterite from Pakistan was measured by the polarized spectra at room temperature to 1000 °C, showing four unambiguous absorption bands at 3612, 3597, 3579, and 3566 cm−1. Here, we report angle-resolved polarized IR spectroscopy of the crystal-oriented forsterite, which were heated at 1 bar up to 1000 °C in situ to investigate the hydrogen diffusion character. The peak positions of the IR absorbance at 3579 cm−1, 3597 cm−1, and 3566 cm−1 of forsterite decreased linearly depending on the temperature, while the 3612 cm−1 is stable. We discuss that the dipole orientation of the hydroxyl is analyzed by a pleochroic scheme of the integrated absorbance vs. sample to polarizer angle. Our data suggest that the temperature effect cannot be ignored since the absorption coefficients and absorbance band positions of OH may alter. Full article
(This article belongs to the Special Issue Gem Crystals)
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11 pages, 4335 KiB  
Article
Study on Gemological Characteristics of Blue Sapphires from Baw-Mar Mine, Mogok, Myanmar
by Siming Chen, Honglin Tan, Cun Zhang, Yajun Teng and Endong Zu
Crystals 2021, 11(11), 1275; https://doi.org/10.3390/cryst11111275 - 21 Oct 2021
Cited by 6 | Viewed by 5089
Abstract
This paper employs an X-ray powder crystal diffractometer (XRD), an X-ray fluorescence spectrometer (XRF), an ultraviolet-visible-near infrared spectrometer (UV-Vis-NIR), a Fourier infrared spectrometer (FTIR), and a laser Raman spectrometer to systematically investigate the gemological characteristics of blue sapphires from Baw-mar mine, Mogok, Myanmar. [...] Read more.
This paper employs an X-ray powder crystal diffractometer (XRD), an X-ray fluorescence spectrometer (XRF), an ultraviolet-visible-near infrared spectrometer (UV-Vis-NIR), a Fourier infrared spectrometer (FTIR), and a laser Raman spectrometer to systematically investigate the gemological characteristics of blue sapphires from Baw-mar mine, Mogok, Myanmar. The results show that the FTIR spectra and UV-Vis-NIR spectra of the sapphire from this mine are significantly different from those of sapphires from other origins, which can be used to identify sapphires from this mine. The main crystal structure of the mineral sapphire from Baw-mar mine is corundum. The predominant chemical elements are Al and O, and the color-causing elements are Fe, Ti, V, and Ni. The characteristic ultraviolet absorption peak appears at 418 nm, which is mainly caused by the d-d transition of V3+ ions. The intensity change of the 946 nm ultraviolet absorption peak indicates that the presence of Ni2+ ions may aggravate the gray tone of sapphire and reduces its transparency. Compared with sapphires from other origins, sapphires from this mine have three characteristic infrared peaks of kaolinite at 930, 1025, and 1110 cm−1, of which the single peak at 930 cm−1 is attributed to -OH translation, and the double peaks at 1025 and 1110 cm−1 are attributed to the Si-O stretching vibration. The peaks at 369, 410, 437, 565, 633, and 739 cm−1 in the Raman spectra are attributed to [AlO6] octahedron vibration. Our work provides insight into detailed spectroscopy data of blue sapphires from this mine and the identification of sapphires from different origins through spectroscopic characteristics. Full article
(This article belongs to the Special Issue Gem Crystals)
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17 pages, 6849 KiB  
Article
Spectroscopic Identification of Amber Imitations: Different Pressure and Temperature Treatments of Copal Resins
by Ting Zheng, Haibo Li, Taijin Lu, Xiaoming Chen, Bowen Li and Yingying Liu
Crystals 2021, 11(10), 1223; https://doi.org/10.3390/cryst11101223 - 11 Oct 2021
Cited by 3 | Viewed by 2198
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Gem Crystals)
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7 pages, 2483 KiB  
Article
Study on the Microstructure and Spectra of Regrown Quartz Crystals from Chinese Jewelry Market
by Danyi Zhou, Taijin Lu, Huiru Dai, Jieran Lv, Shouming Chen, Zhonghua Song and Jian Zhang
Crystals 2021, 11(9), 1145; https://doi.org/10.3390/cryst11091145 - 19 Sep 2021
Cited by 1 | Viewed by 2644
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Gem Crystals)
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11 pages, 2075 KiB  
Article
Near-Infrared Spectroscopy Study of Serpentine Minerals and Assignment of the OH Group
by Shaokun Wu, Mingyue He, Mei Yang, Biyao Zhang, Feng Wang and Qianzhi Li
Crystals 2021, 11(9), 1130; https://doi.org/10.3390/cryst11091130 - 17 Sep 2021
Cited by 10 | Viewed by 2751
Abstract
Three different kinds of serpentine mineral samples were investigated using Fourier transform near-infrared spectroscopy (FTNIR). The results show that there are obvious differences in the characteristic infrared spectra of the three serpentine group minerals (lizardite, chrysotile, and antigorite), which can easily be used [...] Read more.
Three different kinds of serpentine mineral samples were investigated using Fourier transform near-infrared spectroscopy (FTNIR). The results show that there are obvious differences in the characteristic infrared spectra of the three serpentine group minerals (lizardite, chrysotile, and antigorite), which can easily be used to identify these serpentine minerals. The combination of weak and strong peaks in the spectrum of lizardite appears at 3650 and 3690 cm−1, while the intensities of the peaks at 4281 and 4301 cm−1 (at 7233 and 7241 cm−1, respectively) are similar. A combination of weak and strong peaks in chrysotile appears at 3648 and 3689 cm−1 and at 4279 and 4302 cm−1, and a single strong peak appears at 7233 cm−1. In antigorite, there are strong single peaks at 3674, 4301, and 7231 cm−1, and the remaining peaks are shoulder peaks or are not obvious. The structural OH mainly appears as characteristic peaks in four regions, 500–720, 3600–3750, 4000–4600, and 7000–7600 cm−1, corresponding to the OH bending vibration, the OH stretching vibration, the OH secondary combination vibration, and the OH overtone vibration, respectively. In the combined frequency vibration region, the characteristic peak near 4300 cm−1 is formed by the combination of the internal and external stretching vibrations and bending vibrations of the structural OH group. The overtone vibrations of the OH stretching vibration appear near 7200 cm−1, and the practical factor is about 1.965. The near-infrared spectra of serpentine minerals are closely related to their structural differences and isomorphous substitutions. Therefore, near-infrared spectroscopy can be used to identify serpentine species and provides a basis for studies on the genesis and metallogenic environment of these minerals. Full article
(This article belongs to the Special Issue Gem Crystals)
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7 pages, 9499 KiB  
Article
Thermal Process of Rock Crystal: Cause of Infrared Absorption Band at 3585 cm−1
by Jianjun Li, Yuyu Zheng, Xuesong Liu, Guihua Li, Xiaoyan Yu, Yue Wang, Hejun Li, Haibin Liu, Guangqi Shan, Ting Li, Xiuyun Ding, Xiaoxue Zhao, Zhun Huang, Ran Du, Minmin Tian, Fei Yan and Bing Sun
Crystals 2021, 11(9), 1083; https://doi.org/10.3390/cryst11091083 - 6 Sep 2021
Cited by 1 | Viewed by 1759
Abstract
Synthetic rock crystals often show a typical infrared (IR) absorption band at 3585 cm−1. However, the authors recently found this band in a natural rock crystal with blue coating. The origin of this IR band is controversial as yet. In this [...] Read more.
Synthetic rock crystals often show a typical infrared (IR) absorption band at 3585 cm−1. However, the authors recently found this band in a natural rock crystal with blue coating. The origin of this IR band is controversial as yet. In this paper, the infrared spectra of several natural and synthetic rock crystal samples which were heated to 673 K and 1073 K were measured after these samples returned to room temperature. Comparing the infrared spectra of samples before and after heating, we found the absorption band at 3585 cm−1 was induced by the thermal process, which indicates that this band cannot be used as diagnostic evidence for synthetic rock crystal alone. In addition, the LiOH bands decreased while AlOH bands increased upon thermal processing. And the negative correlation between the LiOH bands and the 3585 cm−1 band was also distinct. The above results reveal that the thermal process destroyed the LiOH defects, leading to the formation of a new AlLi defect. And the isolated OH defect inside dislocations generated upon thermal processing is considered to be the exact cause of the 3585 cm−1 band. Full article
(This article belongs to the Special Issue Gem Crystals)
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11 pages, 42244 KiB  
Article
Identification of Pink-Coloured CVD Synthetic Diamonds from Huzhou Sino-C Semiconductor Co. in China
by Zhonghua Song, Huiru Dai, Bo Gao and Wenfang Zhu
Crystals 2021, 11(8), 872; https://doi.org/10.3390/cryst11080872 - 27 Jul 2021
Cited by 1 | Viewed by 3360
Abstract
In recent years, increasing numbers of pink-coloured CVD synthetic diamonds have appeared on the market. One of the major sources is Huzhou SinoC Semiconductor Science and Technology Co., Ltd., Zhejiang province of China. In this article, seven pink-coloured CVD-grown diamonds produced in the [...] Read more.
In recent years, increasing numbers of pink-coloured CVD synthetic diamonds have appeared on the market. One of the major sources is Huzhou SinoC Semiconductor Science and Technology Co., Ltd., Zhejiang province of China. In this article, seven pink-coloured CVD-grown diamonds produced in the last two years by Huzhou have been investigated and identified, including their gemological and spectroscopic characteristics. In DiamondView, they fluoresced orange–red, with an obscure striated growth structure, which is common for CVD synthetics. The mid-IR absorption spectra of these samples showed some single nitrogen and hydrogen-related features (1130, 1344, 3123, 3323 cm−1), which indicated that the diamonds were type Ib and were CVD-grown diamonds. The H1a defect annealed out at approximately 1400 °C, whereas the 3107 cm−1 defect was produced by annealing above 1700 or 1800 °C. This implied that the samples had undergone two separate heat treatments: first, a high-temperature anneal (possibly an HPHT treatment to reduce any brown colour), which would have produced the 3107 cm−1 defects and a small number of A centres, followed by irradiation, followed by annealing above 800 °C to make the vacancies mobile. The UV–Vis–NIR absorption spectra showed distinct NV-related features (575 and 637 nm), the main reason for the pink colour. Photoluminescence spectra obtained at liquid nitrogen temperature recorded radiation-related emissions (388.9, 503.5 nm), a strong N-V centre, H3 and H2 defects, and many unassigned emissions. These pink CVD products can be separated from natural and treated pink-coloured diamonds by a combination of optical spectroscopic properties, such as fluorescence colour, and absorption features in the infrared and UV–Vis regions. Full article
(This article belongs to the Special Issue Gem Crystals)
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23 pages, 4359 KiB  
Article
A Study on Beryl in the Cuonadong Be-W-Sn Polymetallic Deposit, Longzi County, Tibet, China
by Jia-Qi Shen, Zhi-Kang Hu, Shi-Yuan Cui, Yu-Fei Zhang, En-Qi Li, Wei Liang and Bo Xu
Crystals 2021, 11(7), 777; https://doi.org/10.3390/cryst11070777 - 2 Jul 2021
Cited by 6 | Viewed by 2629
Abstract
Recently, aquamarine was discovered in the Cuonadong Be-W-Sn Polymetallic Deposit, Longzi County, Tibet. Longzi aquamarine is being extracted and is expected to be available over the next decade. This study provides a full set of data through standard gemmological properties, including scenes, color [...] Read more.
Recently, aquamarine was discovered in the Cuonadong Be-W-Sn Polymetallic Deposit, Longzi County, Tibet. Longzi aquamarine is being extracted and is expected to be available over the next decade. This study provides a full set of data through standard gemmological properties, including scenes, color characteristics and advanced spectroscopic and chemical analyses, including micro ultraviolet–visible–near-infrared (UV–Vis–NIR), Raman and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The main inclusions in Longzi aquamarine are gas–liquid inclusions and a great number of quartz inclusions. The content of type I H2O is greater than that of type II H2O because of the low-alkali metal content, and “tetrahedral” substitutions and “octahedral” substitutions exist at the same time. Full article
(This article belongs to the Special Issue Gem Crystals)
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11 pages, 4253 KiB  
Article
Study of the Preferred Orientation of Hydroxyapatite in Ivory from Zimbabwe and Mammoth Ivory from Siberia
by Xueying Sun, Mingyue He and Jinlin Wu
Crystals 2021, 11(5), 572; https://doi.org/10.3390/cryst11050572 - 20 May 2021
Cited by 1 | Viewed by 2303
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Gem Crystals)
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Review

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24 pages, 4704 KiB  
Review
Diamond and Other Exotic Mineral-Bearing Ophiolites on the Globe: A Key to Understand the Discovery of New Minerals and Formation of Ophiolitic Podiform Chromitite
by Fei Liu, Dongyang Lian, Weiwei Wu and Jingsui Yang
Crystals 2021, 11(11), 1362; https://doi.org/10.3390/cryst11111362 - 8 Nov 2021
Cited by 3 | Viewed by 2966
Abstract
Ophiolite-hosted diamond from peridotites and podiform chromitites significantly differs from those of kimberlitic diamond and ultra-high pressure (UHP) metamorphic diamond in terms of occurrence, mineral inclusion, as well as carbon and nitrogen isotopic composition. In this review, we briefly summarize the global distribution [...] Read more.
Ophiolite-hosted diamond from peridotites and podiform chromitites significantly differs from those of kimberlitic diamond and ultra-high pressure (UHP) metamorphic diamond in terms of occurrence, mineral inclusion, as well as carbon and nitrogen isotopic composition. In this review, we briefly summarize the global distribution of twenty-five diamond-bearing ophiolites in different suture zones and outline the bulk-rock compositions, mineral and particular Re-Os isotopic systematics of these ophiolitic chromitites and host peridotites. These data indicate that the subcontinental lithospheric mantle is likely involved in the formation of podiform chromitite. We also provide an overview of the UHP textures and unusual mineral assemblages, including diamonds, other UHP minerals (e.g., moissanite, coesite) and crustal minerals, which robustly offer evidence of crustal recycling in the deep mantle along the suprasubduction zone (SSZ) and then being transported to shallow mantle depths by asthenospheric mantle upwelling in mid-ocean-ridge and SSZ settings. A systematic comparison between four main genetic models provides insights into our understanding of the origin of ophiolite-hosted diamond and the formation of podiform chromitite. Diamond-bearing peridotites and chromitites in ophiolites are important objects to discover new minerals from the deep earth and provide clues on the chemical composition and the physical condition of the deep mantle. Full article
(This article belongs to the Special Issue Gem Crystals)
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22 pages, 3528 KiB  
Review
Overview of Gemstone Resources in China
by Xiao-Yan Yu, Zheng-Yu Long, Yi Zhang, Li-Jie Qin, Cun Zhang, Zhi-Rong Xie, Yu-Rui Wu, Ying Yan, Ming-Ke Wu and Jia-Xin Wan
Crystals 2021, 11(10), 1189; https://doi.org/10.3390/cryst11101189 - 29 Sep 2021
Cited by 18 | Viewed by 12190
Abstract
Gemstones are minerals of gem qualities used for adornment and decoration with the attributes of beauty, durability and rarity. Traditionally, although China has been regarded as the most important source for nephrite, over the past decades, a large variety of gemstone resources have [...] Read more.
Gemstones are minerals of gem qualities used for adornment and decoration with the attributes of beauty, durability and rarity. Traditionally, although China has been regarded as the most important source for nephrite, over the past decades, a large variety of gemstone resources have been newly discovered in China owing to continuous exploration works. The vast land with various geological and geochemical backgrounds is rich in gemstone resources with potential for new deposits discoveries. In pegmatites, gemstones are related to granitic magma events and mainly occur in pegmatitic cavities, such as tourmaline, aquamarine, spodumene, spessartine, moonstone, quartz, apatite, and topaz. The eruption of Tertiary basaltic magma provides gem-quality sapphire, spinel, olivine, garnet, and zircon. The supergene oxidation zones of some copper and iron deposits in Hubei and Anhui province host gem-quality turquoise and malachite. Moreover, the formation of the nephrite deposit in China is mostly related to the carbonatite and serpentinite rocks involved in the metamorphic-metasomatic processes. This paper comprehensively introduces the distribution of gemstones deposits, as well as the gemological and mineralogical characteristics of gemstones in China. Our present investigation provides insights into the gemstone potential of China for further exploitation. Full article
(This article belongs to the Special Issue Gem Crystals)
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