An overview of Tourmaline mineralogy from gem tourmaline producing pegmatite districts in Africa

Abstract

Suites of gem-quality faceted tourmaline, slices and fragments from Nigeria Namibia, Mali, Tanzania, Congo and Mozambique were quantitatively analyzed to determine mineralogy and minor element chemistry. The specimens range in color from colorless to pink, red, yellowish-brown, green, bluish-gray, blue, brown and black. The results show that these tourmalines are elbaite, liddicoatite, rossmanite and schorl. Fe, Mn and Ti are the principal chromophores of the studied tourmaline. Fe is the most dominant and causes green, blue, dark-brown and black colors. Mn imparts pink and red hues. Correlations between Mn content and pink color intensity were not found. The Mn2+m,A¡m AªTi4+ charge transfer causes yellowish-brown colors. A positive correlation of Na+ with transition element content was found. Limited relationships between chemistry and locality were deciphered for Nigeria, Namibia and Tanzania on the basis of endmember content and Congo based on Mn, Mg and Ti content.