Publication: Blue zircon from Ratanakiri, Cambodia
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Issued Date
2018
Resource Type
File Type
application/pdf
ISSN
13554565
Other identifier(s)
2-s2.0-85053166985
Rights Holder(s)
Scopus
Bibliographic Citation
Journal of Gemmology. Vol 36, No.2 (2018), p.112-133
Suggested Citation
Zeug M., Nasdala L., Wanthanachaisaeng B., Balmer W.A., Corfu F., Wildner M. Blue zircon from Ratanakiri, Cambodia. Journal of Gemmology. Vol 36, No.2 (2018), p.112-133. doi:10.15506/JoG.2018.36.2.112 Retrieved from: https://hdl.handle.net/20.500.14740/3963
Abstract
Zircon from Ratanakiri Province, north-eastern Cambodia, is well known in the gem trade for its vivid blue colour that results from heat treatment. The untreated brown material turns blue under reducing conditions at ~900-1,000°C. Ratanakiri zircon is characterised by remarkably low contents of trace elements. In particular, the actinides have low concentrations (e.g. approximately 120 ppm U and 95 ppm Th). Together with the very young age of the zircon ( < 1 million years [Ma]), this results in an extremely low self-irradiation dose, which in turn is in agreement with its non-radiation-damaged, nearly perfectly crystalline state. The heat treatment, therefore, does not result in detectable changes in the zircon's structural state. The cause of the blue colour, presumably related to a valence change upon heating in the reducing environment, is still under debate. The absorption of the treated Ratanakiri zircon is decidedly different from that of blue U4+-doped and blue V4+-doped synthetic ZrSiO4. Absorption spectra show a strongly pleochroic band at 18,200- 13,000 cm-1 (corresponding to ~550-770 nm wavelength) that is clearly responsible for the treated blue colour; however, its assignment remains unresolved. © 2018 The Gemmological Association of Great Britain.