Paraíba Tourmaline chromophore—Cu or Fe: that is the question.

Abstract

Laboratory Manual Harmonisation Committee (LMHC) recently updated the definition of Paraíba tourmaline by adding extra descriptions. One of them is about o-ray polarized spectrum to consider some Fe-rich cuprian tourmalines. However, absorption spectra can be incorrect depending on the gemstones’ facetted nature and transparency conditions. Simple comparison of absorption intensities at approximately 700 nm and 900 nm might cause misleading results. Because the definition is based on Cu and Fe, accurate absorption intensities by these elements is necessary. This study suggests a judging method of which element is the dominant chromophore basing on the simulation with trace element concentrations.