Gem-quality garnets: correlations between gemmological properties, chemical composition and infrared spectroscopy

Adamo, Ilaria; Pavese, Alessandro; Prosperi, Loredana; Diella, Valeria; Ajò, D.

doi:10.15506/jog.2007.30.5.307

Cited by 5 publications

(25 citation statements)

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“…In this fi gure, for clarity we have shown only the two principal garnet ternary diagrams, but clearly one could draw in all the others. Other results presented below from pyropes and almandines plot within the grossular- Figure 6: Plot of RI versus magnetic susceptibility for the garnet end-member data of Adamo et al 7 Red crosses are calculated for all end-members found, blue crosses are for the three main endmembers of each series.…”

Section: Proposed New Garnet Characterization Techniquementioning

confidence: 82%

“…It would be expected that since the Mali garnets are almost entirely grossular-andradite, only one property is needed to defi ne the chemistry and RI would do this. Magnetic susceptibility, a better approach to defining garnets Adamo et al 7 recently described correlations between physical properties and chemistry for 17 gem-quality garnets in both the ugrandite and pyralspite groups, and also examined IR spectral features to see what they may contribute to classifi cation of the garnets. They concluded that IR spectra, in particular, permit discrimination between the pyralspite and ugrandite series.…”

Section: Historymentioning

confidence: 99%

“…Adamo et al 7 used the same garnet nomenclature as Stockton and Manson 5 but added the variety grossular-andradite, based on the work of Johnson et al 6 It was in 1933 that Winchell divided the garnet group into two series composed each of three major garnet speciesthe ugrandite series (uvarovite, grossular, andradite), and the pyralspite series (pyrope, almandine, spessartine). These two mineralogical series do not appear to be as well known to gemmologists as they should be.…”

Section: Historymentioning

confidence: 99%

“…Most gemmologists classify garnets based on their colour, refractive index (RI) and absorption spectrum 1,2,3,4,5,6,7 . As new sources and new gem varieties of garnet are discovered, and as our information on garnet chemistry increases, problems with the present gemmological classifi cation become more apparent 8 .…”

Section: Introductionmentioning

confidence: 99%

“…Due to the diffi culty of getting suffi cient compositional information quickly and easily, gemmology has generally followed a different nomenclature, opting to defi ne nine varieties of garnets: pyrope, pyropealmandine, almandine, almandinespessartine, spessartine, spessartinepyrope, grossular, grossular-andradite, and andradite 5,6,7 . Uvarovite is normally not included as it has limited gem signifi cance.…”

Section: Introductionmentioning

confidence: 99%

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Lu¹,

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et al. 2008

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Section: Proposed New Garnet Characterization Techniquementioning

confidence: 82%

Section: Historymentioning

confidence: 99%

Section: Historymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A fancy reddish brown diamond with new optical absorption features

Lu¹,

Odaki²,

Yasunaga³

et al. 2008

Journ of Gemm

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Spectroscopic Study on the Species and Color Differences of Gem-Quality Red Garnets from Malawi

2022

Journal of Spectroscopy

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To reveal the species of gem-grade red garnets with similar colors, especially the mechanisms underlying their subtle color differences, a series of tests, including conventional gemological tests, X-ray diffraction, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, and X-ray photoelectron spectroscopy, were performed on gem-grade red garnets mined from Malawi. The results demonstrated that the color difference is not caused by the difference in species, and both the purplish-red and maroon-red garnets were magnesium-aluminum garnets (pyrope). They both contained the transition metal ions Fe2+, Mn2+, Fe3+, and Cr3+, with Fe2+ and Mn2+ occupying crystal site A and Fe3+ and Cr3+ occupying crystal site B. Cr3+ absorption peaks were observed at 367 and 690 nm; Fe3+ absorption peaks were observed at 502, 528, and 570 nm; and Mn2+ absorption peaks were observed at 400, 423, and 460 nm, which contributed to their respective colors. However, while the maroon-red pyrope had a larger Fe2+/Fe3+ ratio than the purplish-red pyrope, it lacked Mn2+ ions, which is the cause of the color difference between the two pyrope garnets. To date, the study of color differences in red garnets remains a major controversial topic. This study proposed an innovative spectroscopic approach, particularly the combination of ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy, thus providing a novel methodology for investigating color differences in red garnets.

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Magnetic susceptibility, a better approach to defining garnets

Hoover¹,

Williams²,

Williams³

et al. 2008

Journ of Gemm

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Using a new, non-destructive method of gem testing, magnetic susceptibility, the authors show how the major endmember composition of any garnet may be confi dently predicted by plotting RI against measured susceptibility. On this diagram, eight end-member garnets are plotted, so that any measured garnet can be placed in an appropriate ternary area. This method shows how previous methods of identifying garnetsby their colour, RI and spectrumare insuffi cient to accurately identify chemistry in the garnet group. Furthermore, it can be done with inexpensive equipment available to most gemmologists.

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Gem-quality garnets: correlations between gemmological properties, chemical composition and infrared spectroscopy

Cited by 5 publications

References 0 publications

A fancy reddish brown diamond with new optical absorption features

A fancy reddish brown diamond with new optical absorption features

Spectroscopic Study on the Species and Color Differences of Gem-Quality Red Garnets from Malawi

Magnetic susceptibility, a better approach to defining garnets

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