“…Numerous studies have addressed the problem of identifying the geological sources of obsidian, dating, techniques for mining and working the obsidian, and cultural exchange relationships in Mesoamerica (e.g., Spence, 1967;Meighan et al, 1968;Cobean et al, 1971;Hammond, 1972;Stross et al, 1978Stross et al, , 1983Pastrana, 1986;Gaxiola and Clark, 1989). The petrological and chemical properties of obsidians from several localities in central Mexico and from archaeological sites were discussed by Ordóñez (1892), Ericson and Kimerlein (1977), Darras (1987), Mosheim and Althaus (1988), Dahl et al (1990), Joron et al (1990) and Darling (1993). Special attention has been paid to studies of trace elements using a variety of techniques such as x-ray fluorescence, neutron activation analysis and optical spectroscopy.…”