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Dahl, Peter, B Harkness, and G Maurath. 1990. “Trace-Element Analysis of Mayan Obsidian Blades from Yucatan and Campeche Provinces, Mexico”. Chemical Geology. https://doi.org/10.1016/0009-2541(90)90110-S.
Dahl, Peter, et al. Trace-Element Analysis of Mayan Obsidian Blades from Yucatan and Campeche Provinces, Mexico. Chemical Geology, 15 Oct. 1990, https://doi.org/10.1016/0009-2541(90)90110-S.