Investigaciones químicas y ópticas de obsidianas geológicas y arqueológicas de México

Abstract

A physical method is described for the assignment of archaeological obsidian sarnples to their geological sources for the sake of reconstruction of trade relations. Microscope Photometry has proved to be a good method to characterize the absorption behaviour of obsidians in the range of UV, VIS, and NIR. The appropriate presentation ofthe data is a plot of the tangent of the slope angles of the absorption curves against the position of the extinction maximum. This procedure results in clusters of the geological sources to which the archaeological samples - after an analogous treatrnent - can be easily assigned. Th!l absorption behaviour of obsidians is directly related to their chemical composition. Therefore, it has to be clarified in advance, whether the 41 analyzed obsidians of the Mexican Volcanic Belt (MVB) vary sufficiently in their chemical composition. Major- and trace element determination and the plot of the data in correlation diagrams result in different clusters for all the analyzed Mexican obsidians. Opticiil measurements can be carritld out, based on the knowledge of the chemical variation. Thus, 108 obsidian artifacts of the Central Mexican Highland can be assigned to the following supply areas: In the western part of the MVB: Mesa de Las Salvias, Nayarit (also called Ixtlán del Río) and, less important, Tequila and La Primavera, Jalisco. In the central part of the MVB: San José, Michoacán (also called Zinapécuaro), Cerro de Las Navajas, Hidalgo (also called Pachuca), and, less important. Querétaro, Querétaro and Buenavista, Estado de México (also called Barranca de Los Estetics or Otumba) with extensive inanufacturing areas. In the eastern part of the MVB: Altotonga, Veracruz, Zaragoza, Puebla and Jacal, Veracruz (also called Pico de Orizaba) with cxtensive manufacturing areas.