Geochemical Characterization and Gemological Suitability of African Gem Tourmalines, Nigerian Tourmalines: A Case Study

Abstract

Tourmaline, a versatile gem-mineral with a diverse array of colours, has long captivated gem enthusiasts and researchers alike. Nigeria is a significant source for gem-quality tourmalines, highly prized for their vibrant hues. This study presents a comprehensive geochemical analysis of Nigerian tourmalines, aiming to elucidate their compositional variations and gemological significance. Analytical results revealed moderate SiO₂ (av. 45.68%) and Al₂O₃ (av. 34.40%), but depletion in the other major oxides. Incompatible elements are significantly concentrated in a few of the analyzed samples, making Cs the most variable (0.05 - 8863.00ppm), suggesting different petrogenetic processes and sources of magmatic or hydrothermal fluids, thus providing insights into the genesis and evolution of the host rocks. Elevated Be values (>10,000ppm) were observed for some samples, confirming tourmaline’s use as an exploratory tool for other mineralizations. All the studied tourmaline samples plot into the fields of Li-rich granitoid pegmatites and aplites of the Al-Fe-Mg plot.