Obsidian, a black volcanic glass, was first recognized by Colin Renfrew and his colleagues J.E. Dixon and J.R. Cann in the 1960s as a uniquely sensitive indicator of prehistoric trade, both because of the great desirability of this material before the use of metals, and also because the trace-elements it contains are usually diagnostic of individual sources. Based on data extracted from M.-C. Cauvin et al., L'obsidienne au Proche et Moyen Orient: du volcan à l'outil (Oxford: BAR Int. Ser. 738), maps indicate the flows of material from two major source-areas.