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Gemstone Analysis by Spectroscopy and Microscopy, Volume II

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Crystallography and Physical Chemistry of Minerals & Nanominerals".

Deadline for manuscript submissions: closed (15 May 2023) | Viewed by 9651

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Special Issue Editor

Dr. Thomas Hainschwang

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Guest Editor

GGTL Laboratories Liechtenstein, Gnetsch 42, 9496 Balzers, Liechtenstein
Interests: fancy colour diamonds (spectroscopy and imaging; treatments); gemstone spectroscopy; gem testing instrument developments; gem treatments
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The analysis of gemstones used to be a task mostly performed on basic optical instruments such as refractometers by gemmologists. This has changed significantly over the past several decades, and gem testing has become a highly sophisticated field of science that combines mineralogy, geology, chemistry, and physics. Gem materials are typically split into diamonds (colourless and coloured), coloured stones (all other gemstones) and organic materials such as pearls, amber and coral. Gemstone analysis involves a range of tasks including identification, treatment detection, country of origin detection, the determination of colour-causing mechanisms, the analysis of impurities and defects, plus the analysis of the growth mechanisms responsible for the specific physical characteristics of gem materials.

This Special Issue focusses on the spectroscopic and microscopic analysis of gemstones, including all types of spectroscopic and microscopic techniques used in the characterisation of gem materials. Papers are welcome that cover new analytical results obtained from testing gem materials by spectroscopy and/or microscopy, including new or little-exploited methods. Such results may include—amongst others—the characterization of specific gem materials, defect characterization of gemstones, the characterization and identification of gem treatments, and the application of new or little-exploited spectroscopic or microscopic analytical techniques. Submitted papers may cover any type of gem material, including natural, synthetic and artificial gemstones, untreated and treated.

Dr. Thomas Hainschwang
Guest Editor

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. Minerals 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 2400 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

defect characterization
gem material characterization
treatment characterization
colour origin
spectroscopy
microscopy

Related Special Issue

Gemstone Analysis by Spectroscopy and Microscopy in Minerals (10 articles)

Published Papers (6 papers)

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Research

23 pages, 9485 KiB

Open AccessArticle

Evaluation of the Gemological Properties of Datolites from the Campotrera Deposit in the Northern Apennines (Italy)

by Luigi Marinoni, Franca Caucia, Mattia Gilio and Maurizio Scacchetti

Minerals 2023, 13(8), 1057; https://doi.org/10.3390/min13081057 - 11 Aug 2023

Viewed by 801

Abstract

This work investigates the gemological properties of the datolite from the famous field of Campotrera near Reggio Emilia in Italy, for a possible commercial use in the market. This mineral occurs in widespread multi-centimeter veins, together with calcite and prehnite, within polygenic breccias in basaltic ophiolites. The most common form for this datolite is the double wedge with a prism (110) and a pinacoid (001). The gems obtained are mixed or carré cut, colorless or salmon pink, transparent, with a vitreous luster and weight between 1 to 5 carats. They have high brilliance, transparency and birefringence, glassy luster, absence of cleavage. The major chromophore is probably Fe, which occurs as inclusion of hematite and ilmenite. Raman investigations highlighted different fluid inclusions. The primary are randomly distributed or, in some cases, follow the growth zones, while the secondary form aligned tracks along the microcracks. Fluid inclusions can be biphasic and made up by liquid + gas (L + G), generally >10 mm in size, and more rarely, monophasic, composed only by liquid (L) generally <10 mm. The gems extracted from the rough sample are very valuable but their delicacy requires attention in the cutting and preparation of the jewels. Full article

(This article belongs to the Special Issue Gemstone Analysis by Spectroscopy and Microscopy, Volume II)

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14 pages, 4166 KiB

Open AccessArticle

Nature of Pigments in Orange and Purple Coloured Chinese Freshwater Cultured Pearls: Insights from Experimental Raman Spectroscopy and DFT Calculations

by Chaoyang Chen, Jing Yu, Chuting Zhang, Xu Ye and Andy H. Shen

Minerals 2023, 13(7), 959; https://doi.org/10.3390/min13070959 - 18 Jul 2023

Cited by 1 | Viewed by 1391

Abstract

Pearls, a well-known organic gemstone, are popular for their attractive lustre and rich colour. The pigmentation and colour of pearls have never been clearly explained. Understanding the pigments and colour origin of pearls can be a guide for artificial cultivation and rational conservation. In this study, Chinese freshwater cultured pearls were collected as research samples. The appearance and colour characteristics of pearls were characterised using D65 standard light source photography and UV–Vis spectroscopy, the molecular structure of the pigments in the pearls was characterised using Raman spectroscopy, and Density Functional Theory (DFT) calculations were used to reveal the characteristics of the pigments in the pearls in terms of molecular structure and electronic excitation. It was proposed that freshwater pearls are coloured with polyene pigments, with the chain length of the polyene determining the type of colour and the concentration of the polyene determining the colour intensity of the pearl. The HOMO–LUMO transition of conjugated polyenes is intrinsically responsible for the colour of pearls. Many colour-rich biominerals also have similar Raman spectral features to pearls, and this study has wider implications for understanding the nature of pigments and their colour origins. Full article

(This article belongs to the Special Issue Gemstone Analysis by Spectroscopy and Microscopy, Volume II)

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14 pages, 7237 KiB

Open AccessArticle

Deciphering the Color Origin of Pink Conch Pearl Using Nondestructive Spectroscopies and DFT Calculations

by Chaoyang Chen, Jing Yu, Xu Ye and Andy H. Shen

Minerals 2023, 13(6), 811; https://doi.org/10.3390/min13060811 - 14 Jun 2023

Cited by 1 | Viewed by 1095

Abstract

Conch pearl is a calcareous concretion produced by the Queen conch mollusk and is of extremely high economic value. Its attractive pink color has remained a mystery for hundreds of years. This difficulty limits the development of cultivation and preservation technology of conch pearl. Due to its super-high value, it is generally impossible to use destructive chemical analysis methods. Here, various nondestructive spectroscopic analysis methods and theoretical calculations were used to reveal the color origin of pink conch pearl. The experimental Raman and UV-Vis spectroscopies were used to characterize the color and pigments. We further discuss the pigments in conch pearl by comparing the Raman spectral characteristics and pigments of the red coral. Based on the characteristics of the experimental spectra, we speculate that the carotenoids color the conch pearl. The theoretical Raman and UV-Vis spectra of all-trans polyene and carotenoids were simulated using DFT calculations. According to the results, we proposed that the pigments in pink conch pearl are polyenes containing 11 shortened C–C bonds with multiplicities > 1.5, which may be demethylated carotenoids. Full article

(This article belongs to the Special Issue Gemstone Analysis by Spectroscopy and Microscopy, Volume II)

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9 pages, 2522 KiB

Open AccessArticle

Development of Mid-Infrared Absorption Spectroscopy for Gemstone Analysis

by Zhen Wang and Hiroshi Takahashi

Minerals 2023, 13(5), 625; https://doi.org/10.3390/min13050625 - 29 Apr 2023

Viewed by 1631

Abstract

Absorption spectroscopy has been widely used in gemstone societies as it enables the identification of the origin and post-treatment of gemstones in a non-destructive way. The infrared (IR) range is critical for studies of gemstones such as corundum, emerald, and diamond. Regarding the corundum sample, absorption peaks related to the -OH bond could be used as an index for heat-treatment detection, and different types of inclusions could be identified by analyzing the IR absorption spectrum. The most widely used method for measuring IR absorptions is Fourier-transform infrared spectroscopy (FTIR), which was designed based on the working of the Michelson interferometer. However, FTIR has a few limitations, such as a long measurement time and difficulty in sample placement, which limits its full automation capability. In this study, a mid-infrared (MIR) spectrometer relying on the upconversion phenomenon of non-linear crystals was used to measure the absorption spectra. Corundum with heat treatment features and/or with different common types of inclusions were measured by both transmission and reflection modes. After comparison with the FTIR spectra captured on the same sample set, the same target peaks could be captured with a shorter measurement time and easier operation. The developed MIR spectrometer could directly measure the absorption spectrum in the 2–4.5 µm (2200–5000 cm⁻¹) range within a few seconds. Meanwhile, as both transmission and reflection modes were available, both loose and mounted gemstones could be measured, supporting the widespread use of this device in large-scale production and its ability to achieve full automation. Full article

(This article belongs to the Special Issue Gemstone Analysis by Spectroscopy and Microscopy, Volume II)

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11 pages, 4257 KiB

Open AccessArticle

Gemological and Luminescence Characteristics of Taaffeites from Mogok, Myanmar

by Bihan Lin, Xingtong Li, Longbo Zhang, Xiaojing Lai and Qian Zhang

Minerals 2023, 13(3), 346; https://doi.org/10.3390/min13030346 - 28 Feb 2023

Viewed by 2024

Abstract

Taaffeite is a rare gem that has been found in different localities such as Tanzania, Sri Lanka, China, and Mogok, Myanmar. In this study, thirty-two taaffeite samples from Mogok, Myanmar, were investigated by conventional gemological testing, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), Raman spectrometry, and fluorescence spectrometry. Through microscopic observations, various types of inclusions were observed in these taaffeites, including irregular inclusions, orange and brown intrusions, black dotted and flake inclusions, healed fissures, tubular inclusions, fingerprint inclusions, and multi-phase inclusions. The Raman spectra demonstrated that the inclusions were mainly calcite, forsterite, celestite, graphite, dolomite, and transparent tubular or columnar inclusions filled with CO₂. In previous studies, taaffeite showed inert or chalky fluorescence under long-wave ultraviolet (LWUV) light and inert fluorescence under short-wave ultraviolet (SWUV) light. In this study, the taaffeite samples revealed different fluorescence phenomena under ultraviolet light. Thirty-two taaffeite samples were classified into four categories according to their fluorescence under LWUV: orange-red, pink, green, and blue-white fluorescence. Under SWUV, all samples presented inert to bright pink fluorescence. Two-dimensional fluorescence spectra were obtained through a fluorescence spectrometer. For the samples with orange-red and pink fluorescence under LWUV, two-dimensional fluorescence spectra showed that peaks at 686 nm and 690 nm (in the red region) were strong. For the samples with green and blue-white fluorescence under LWUV, peaks at 439 nm and 464 nm (in the blue region) were strong, peaks at 507–515 nm (in the green region) were relatively weak, and peaks at 686 and 690 nm (in the red region) were very weak. Combined with the data from LA-ICP-MS, it is speculated that Cr³⁺ was responsible for samples having orange-red and pink fluorescence, that Mn²⁺ was responsible for samples having green fluorescence, and that Fe inhibited the generation of fluorescence. Full article

(This article belongs to the Special Issue Gemstone Analysis by Spectroscopy and Microscopy, Volume II)

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13 pages, 3873 KiB

Open AccessArticle

Gemological and Spectroscopic Characteristics of “Jedi” Spinel from Man Sin, Myanmar

by Longpei Zhao, Geng Li and Liqun Weng

Minerals 2022, 12(11), 1359; https://doi.org/10.3390/min12111359 - 26 Oct 2022

Cited by 4 | Viewed by 2007

Abstract

The price of spinel has sharply risen in recent years, and its market acceptance is extending. Among the many sources of spinel, Man Sin in Myanmar is the most famous for its bright neon pinkish red to reddish pink color, named “Jedi” spinel commercially. In this paper, spinel samples with the bright neon pinkish red to reddish pink from Man Sin in Myanmar were studied non-destructively with X-ray fluorescence spectrometer (EDXRF), Fourier transform infrared spectrometer (FTIR), fluorescence spectroscopy, a UV-Vis spectrophotometer and Raman spectroscopy. The results show that the samples from Man Sin in Myanmar are the magnesia-alumina spinels. The high content of the red-chromogenic element Cr, an intermediate content of V and Zn, and a low content of the chromogenic element Fe may be responsible for the distinctive neon color of the spinel samples. The presence of Ti may also serve as a basis for the identification of its origin in Man Sin in Myanmar. The fluorescence spectrum analysis of spinels shows them to have multiple excitation peaks in the region 600–800 nm, which are caused by the jump of Cr³⁺ between the ²E→⁴A₂ inter-energy band lattice. The amount of Zn affects the fluorescence spectrum intensity of spinels. The higher the Zn content, the stronger the fluorescence intensity. The spinel structure is uncomplicated and four more obvious absorption peaks appear in the IR spectrum, and the direction of the absorption peaks is shifted if a homogeneous substitution of the AB₂O₄ structure occurs; the Raman spectra of spinel samples have four vibrational peaks at 100–2000 cm⁻¹, 310 cm⁻¹, 407 cm⁻¹, 665 cm⁻¹ and 763 cm⁻¹, which has spinel species-identification significance. Full article

(This article belongs to the Special Issue Gemstone Analysis by Spectroscopy and Microscopy, Volume II)

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