Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions

Belley, Philippe M.; Palke, Aaron C.

doi:10.5741/gems.57.3.228

Cited by 6 publications

(6 citation statements)

References 11 publications

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“…The T Fe 2+ spin-forbidden transitions 5 E (D)→ 3 E (D) and 5 E (D)→ 3 T2 (G) are responsible for the absorption bands around ~372 nm and ~386 nm, respectively. Moreover, these absorption bands may be amplified by T Fe 2+ -M Fe 3+ ECP transitions [6,20]. Two broad bands at ~458 nm and ~476 nm may be assigned principally to spin-forbidden…”

Section: Uv-vis-nir Spectroscopymentioning

confidence: 99%

“…Two broad bands at ~458 nm and ~476 nm may be assigned principally to spin-forbidden 6 A 1g → 4 A 1g , 4 E g transitions of isolated M Fe 3+ ions, possibly intensified by ECP interactions and by spin-forbidden transitions of T Fe 2+ [6]. The absorption around ~540 nm may be caused by spin-allowed d-d transitions 3 T 1 (F)→ 3 T 2 (F) in V 3+ at the M sites or spin-allowed electronic d-d transitions 4 A 2g → 4 T 2g (F) in Cr 3+ at the M sites [6,9,20,[36][37][38][39][40][41]. (2)…”

Section: Uv-vis-nir Spectroscopymentioning

confidence: 99%

“…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%

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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: Uv-vis-nir Spectroscopymentioning

confidence: 99%

Section: Uv-vis-nir Spectroscopymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Wu¹,

Sun²,

Ma³

et al. 2023

Minerals

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“…The Fe content of purple spinel is obviously higher than that of Cr + V (Figure 17b), and Fe plays a dominant role in purple spinels. Belley et al (2021) found that the relatively low Fe content in Vietnamese purple spinels (<2437 ppm) may be the key to create attractive saturated colors [61]. The Fe content of purple spinel ranges from 1364.84 to 14,237 ppm, with an average value of 5748 ppm.…”

Section: Chromogenic Mechanism Of Spinelmentioning

confidence: 99%

Characterization of Red, Pink, Orange, and Purple Gem-Quality Spinel from Four Important Areas

Xu,

Gao

et al. 2023

Crystals

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Spinel is a precious stone with a long history. In ancient societies spinel was considered to be an imitation of ruby. With the depletion of ruby mineral resources, gem—grade spinel has attracted more and more attention from consumers. In the last decade, as the popularity of spinel in the global colored gem market continues to rise, plenty of domestic and foreign jewelry brands have launched spinel based jewelry. This study takes spinels from Burma, Vietnam, Sri Lanka, and Tanzania as its research objects and performs a series of tests to obtain their gemological characteristics, spectral characteristics, and chemical composition, with the aim of comparing the differences between spinels with different colors from different areas and exploring the chromogenic mechanism of spinels. Only Burmese red spinels have a typical Cr spectrum. The types of inclusions and the contents of trace elements are the main differences between spinels from the four areas. Burmese spinel is characterized by an octahedral negative crystal filled with dolomite or a mixture of dolomite and calcite. Magnesite is present in Sri Lankan spinels, and dolomite is present in Tanzanian spinel. Dislocation systems and the presence of titanite and talc inclusions are strongly indicative features of Vietnamese spinel. Sri Lankan spinel is characterized by abundant gas–liquid inclusions, such as the beaded healing fissure. The trace element contents of the four areas are different. Burmese spinel is poor in Fe and Zn (Fe: 135.68–3925 ppm; Zn: 338.58–1312 ppm), while Burmese red spinel is rich in Cr (up to 7387 ppm). Vietnamese spinel is rich in Fe (3669.63–19,425 ppm) and poor in Ti content (<89 ppm), while Tanzanian spinel is rich in Zn (5129.96–7008 ppm). High content of Cr + V can lead to the red color in spinel, and the contents of Cr and V change obviously with color. Spinels appear red when Cr content is higher than V, while spinels appear orange when V content is higher than Cr. The red, pink, and orange spinels are colored by Cr3+ and V3+, showing a wide absorption band centered at 400 nm and 550 nm. Fe plays a dominant role in purple spinels. The purple spinel is colored by Fe3+ and Fe2+.

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“…Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation, and it is utilized as a valuable tool in mineralogical sciences. There are many researches about the significant effects of fluorescence on the color appearance in minerals in the past decades, such as diamond 8 , ruby 9 , opal 10 , amber 11 , and spinel et al Natural gem-quality spinels are found all over the globe, such as Myanmar 12 , Vietnam 13 – 15 , Afghanistan 15 , Sri Lanka 14 , Tajikistan, and Tanzania 16 . According to the report by Vincent Pardieu, a special variety of natural spinel (typically use as “Jedi spinel” as a commercial name) with a bright neon pinkish-red color was found in Mogok and Mansin in Myanmar 12 .…”

Section: Introductionmentioning

confidence: 99%

Colorimetry characteristics and color contribution of fluorescence in natural Cr-containing spinel

Tang

Guo

Zhang³

2023

Sci Rep

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Fluorescence plays an important role in determining the color appearance of fluorescing minerals. This paper discusses the color mechanism in the red spinel and the color effects from the light source as well as the background on the spinel color. Excitation-Emission Matrices (EEMs) fluorescence spectroscopy was utilized to characterize the fluorescence of natural Cr-doped magnesia-alumina spinel from Myanmar. EMP, LA-ICP-MS, and optical spectroscopy were applied to study the spinel's chemical compositions and color mechanism. X-Rite Ci-7800 spectrophotometer, which is useful to measure colors for fluorescing minerals, was employed to acquire color data of spinel in daylight and incandescent light. The results indicated the higher value of Cr/Fe makes pinkish-red spinel has a much stronger red fluorescence effect than dark-red spinel. The two narrow absorption bands at ~ 25,500 cm−1 (with a broad absorption band at ~ 24,100 cm−1) and ~ 18,570 cm−1 in the optical absorption spectrum are assigned to spin-allowed electronic d-d transitions 4A2g → 4T1g(F) and 4A2g → 4T2g(F) in Cr3+ at the M site. The EEMs spectra of the pinkish-red spinels show twin emissions at 706 nm excited both by ~ 380 nm and ~ 535 nm radiations, which is the key to the bright neon red color in pinkish-red spinel. The colorimetry study suggests the strong red fluorescence produced by < 460 nm radiation contributes more than 10% lightness and chroma in pinkish-red spinel under daylight. The lightness and the chroma of the spinels grow with the decrease of the background grayscale. The differentiation of spinel colors in dark conditions is lower than that in a bright environment.

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Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions

Cited by 6 publications

References 11 publications

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

Characterization of Red, Pink, Orange, and Purple Gem-Quality Spinel from Four Important Areas

Colorimetry characteristics and color contribution of fluorescence in natural Cr-containing spinel

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