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Schmetzer, Karl; Malsy, Anna-Kathrin (2011). Alexandrite and colour-change chrysoberyl from the Lake Manyara alexandrite-emerald deposit in northern Tanzania. Journal of gemmology, 32(5-8), pp. 179-209. Gemmological Association of Great Britain
Schmetzer, Karl; Krzemnicki, Michael; Hänni, Henry; Bernhardt, Heinz-Jürgen; Pettke, Thomas (2007). Gem-quality taaffeites and muscravites from Africa. Journal of gemmology, 30(7-8), pp. 367-382. London: Gemmological Association of Great Britain
Gnos, E.; Mahmood, K.; Khan, M.; Khan, A.S.; Armbruster, Th. (1998). Natrolite from the Bela ophiolite, Pakistan. Journal of gemmology, 26, pp. 308-312. Gemmological Association of Great Britain
