Update on Purple Spinel from Afghanistan

Hänsel, Sebastian; Lhuaamporn, Thanapong; Seneewong-Na-Ayutthaya, Montira; Suphan, Cheewaporn

doi:10.15506/jog.2021.37.7.678

Cited by 2 publications

(1 citation statement)

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“…However, there is little research on purple-violet spinel specifically. Until relatively recently with the new finding of attractive purple spinels in Afghanistan and new deposits in Vietnam [17][18][19][20], purple spinel was often marginalized commercially and has been gradually pursued by consumers. Geologically, gem-quality spinels from Asia and eastern Africa are recovered from various geological settings, mainly marble-hosted deposits.…”

Section: Introductionmentioning

confidence: 99%

Purple-Violet Gem Spinel from Tanzania and Myanmar: Inclusion, Spectroscopy, Chemistry, and Color

Wu¹,

Sun²,

Ma³

et al. 2023

Minerals

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Purple-violet gem spinels from Tanzania and Myanmar have been investigated for their gemological, spectroscopic, chemical, and colorimetric characteristics. Samples TS and MS both had a purple hue with a pinkish or brownish secondary tone and medium–strong saturation. We identified a number of inclusions, including dolomite, phlogopite, and forsterite in Tanzanian spinel and magnesite, apatite, baddeleyite, anhydrite, pyroxene, and graphite in Myanmar spinel. Tanzanian spinels have slightly lower FWHM (full width at half maximum) values of the 406 cm−1 line in the Raman spectrum and the Cr3+ zero phonon line in the PL spectrum compared to samples from Myanmar. Fe, Mn, Cr, V, and Zn are proved as useful discriminators to distinguish these two geographic locations. UV-Vis-NIR spectra and CIE L*a*b* parameters are compared with trace element chemistry. Both samples are colored by Fe2+, with minor Fe3+, Cr3+, and V3+. Cr, V, and Fe are combined to influence the hue angle and lightless of purple spinels from Tanzania. However, due to the relatively stable content in Myanmar samples, Fe shows a minor effect on these two parameters. It is worth noting that all inclusion scene, spectral, and chemical characteristics, as well as the comparison presented in this study are of a limited number of samples from Tanzania and Myanmar.

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Section: Introductionmentioning

confidence: 99%

Purple-Violet Gem Spinel from Tanzania and Myanmar: Inclusion, Spectroscopy, Chemistry, and Color

Wu¹,

Sun²,

Ma³

et al. 2023

Minerals

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Gemological and Chemical Characterization of Varicolored Gem-Grade Spinel from Mogok, Myanmar

Zhao

et al. 2023

Crystals

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Spinel is a precious gem with a long history, but people are far less familiar with it. Previous studies on Mogok spinel from Myanmar focused on inclusion analysis, chromogenic mechanism with a single-color gemstone and heat treatment, whereas systematic studies on varicolored gem-grade spinel are lacking. In this study, the gemological and geochemical analysis of four colors of spinel samples from Mogok were carried out for basic gemology, inclusion morphology and identification, spectroscopy and geochemistry. The aim was to explore the occupation of elements of spinels in the crystal structure, as well as the chromogenic mechanism of varicolored spinels and the geological and geodynamic conditions of the formation. Mogok spinel samples are characterized by octahedral negative crystals filled with calcite and chondrodite inclusions, indicating that they are derived from a marble metamorphic-type deposit. The spinel samples of four colors are magnesia–alumina spinel (MgAl2O4). The contents of V and Cr in Mogok spinel are generally high, with a significant high content of Zn being the most characteristic, and trace elements vary greatly. The infrared spectra of spinel samples in different colors are basically similar. According to the UV–Vis spectrum, pink and red samples are mainly colored by Cr and/or V, whereas orange samples are mainly colored by V. Two wide absorption bands in the range 300~600 nm are mainly attributed to the spin-allowed transition and spin-forbidden transition of Cr3+ and/or V3+. The purple samples are mainly colored by Fe and the UV–Vis spectrum is mainly attributed to the spin-forbidden transition of TFe2+. This study is a favorable supplement to the research on Mogok spinels of various colors from multiple perspectives.

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Update on Purple Spinel from Afghanistan

Cited by 2 publications

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Purple-Violet Gem Spinel from Tanzania and Myanmar: Inclusion, Spectroscopy, Chemistry, and Color

Purple-Violet Gem Spinel from Tanzania and Myanmar: Inclusion, Spectroscopy, Chemistry, and Color

Gemological and Chemical Characterization of Varicolored Gem-Grade Spinel from Mogok, Myanmar

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