Black spinel - a gem material from Bo Phloi, Thailand

Autor(en)
Ágnes Blanka Kruzslicz, Lutz Nasdala, Manfred Wildner, Radek Skoda, Günther J. Redhammer, Christoph A. Hauzenberger, Bhuwadol Wanthanachaisaeng
Abstrakt

The Bo Phloi gem field in Kanchanaburi Province, western Thailand, is renowned mostly for its blue sapphire. Corundum production has now virtually ceased, so local gem cutters are focusing on high-quality black spinel, which is abundant from past stockpiles, to produce various jewellery items and carvings. A detailed mineralogical characterisation of this material showed that it is spinel sensu stricto (MgAl2O4) with elevated Fe contents (20.7 ± 0.9 wt.% FeO, or Mg:Fe atomic ratio about 2:1). The enriched Fe causes the dark colouration of the material. Based on Mössbauer spectroscopic results, Fe occurs in both divalent and trivalent states, the latter occupying both (fourand six-coordinated) cation sites in the crystal structure. The Fe3+ contributes to a ‘partially inverse’ occupation of the cation sites. As a result, the Raman spectrum of Bo Phloi material does not resemble that of ‘normal’ spinel, but rather is similar to the spectra of other spinel-group minerals that tend to show some inversion in their cation-site occupation, such as hercynite, magnetite and magnesioferrite.

Organisation(en)
Institut für Mineralogie und Kristallographie
Externe Organisation(en)
Srinakharinwirot University, Eötvös Loránd University Budapest, Masaryk University, Paris-Lodron Universität Salzburg, Karl-Franzens-Universität Graz
Journal
The Journal of Gemmology
Band
37
Seiten
66–79
Anzahl der Seiten
14
ISSN
1355-4565
DOI
https://doi.org/10.15506/JoG.2020.37.1.66
Publikationsdatum
03-2020
Peer-reviewed
Ja
ÖFOS 2012
104026 Spektroskopie, 105116 Mineralogie
Schlagwörter
Link zum Portal
https://ucris.univie.ac.at/portal/de/publications/black-spinel--a-gem-material-from-bo-phloi-thailand(5ae85454-55f4-461f-b313-c2e900b57ffa).html