Comment on: Application of Raman Spectroscopy to Distinguish Metamorphic and Igneous Zircon (Xian et al., Anal. Lett. 2004, v. 37, p. 119)

Abstract

We critically discuss a recently proposed technique ((Xian et al. 2004)) used to distinguish igneous (i.e., magmatic) from metamorphic growth of the mineral zircon according to the intensity of the 1461 cm⁻¹ band observed in those author's Raman spectra. The band evaluated by Xian et al. (2004) is actually due to laser‐induced photoluminescence of trace amounts of the trivalent rare earth element Er, which, as an analytical artefact, overlays the Raman spectrum when green Ar⁺ laser excitation is used. We demonstrate that this band is not a Raman band, and discuss why the intensity of Er³⁺ luminescence is not uniquely indicative of the geologic origin of a zircon crystal. The technique proposed by Xian et al. (2004) may consequently lead to wrong, and thus misleading results. Therefore, we suggest that this technique should not be used for any petrogenetic assignment of the environment of crystallization for zircon.

Keywords:

• Raman spectroscopy
• luminescence
• photoluminescence spectroscopy
• energy levels
• zircon
• rare‐earth elements