2018/01/01 by Manuela Zeug, Lutz Nasdala, Bhuwadol Wanthanachaisaeng +3 · 1 citation
Earth and Planetary Sciences · #Geochemistry #Geological and Geochemical Analysis #Geology #Mineralogy and Gemology Studies #Paleontology and Stratigraphy of Fossils #Zircon
paper · doi:10.15506/jog.2018.36.2.112
openalex publication_date 2018/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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.