Characteristics of tourmaline for indicator of geographic origin and quality enhancement

Abstract

The objective of this research is to study the characteristics of tourmalines from Brazil, Mozambique, Nigeria, and Madagascar, as well as their physical changes after gamma ray irradiation. Basic equipment and advanced analytical techniques based at the ICA Gem Lab were used for this study. The main aim of this study is to develop database for further identification of geographic origin. Most of 84 tourmaline samples under this study are transparent with abundant internal fractures and inclusions. They are inert without luminescence under UV lamp. Unknown solid inclusions are found in some samples whereas heal fissure, liquid veil, and growth tube are often found in most samples. Based on advanced analyses, strong absorptions caused by Mn, V, Fe, and Cu can be clearly observed in UV-Vis-NIR spectrum. For infrared absorption spectrum, all samples show similar pattern. EDXRF chemical analysis could not be used for tourmaline classification and geographic origin determination. Other techniques should be applied for further analyses. Color of tourmaline after gamma irradiation was changed as a result of charge transfer transition. Infrared absorbance shows a slightly change. Other characteristics include impurities and chemical composition are quite similar to the untreated tourmaline samples.