Saturday, July 10, 2010

Calixtlahuaca Obsidian

By Bradford Andrews

At Calixtlahuaca (like most prehispanic societies in Mesoamerica), obsidian was the most common type of stone used to make tools for a wide variety of domestic, militaristic, and ritualistic purposes. More than 94% of the tools and debitage (byproducts of stone tool manufacture and use) from the site are composed of obsidian. Analysis of the obsidian materials was initiated by me and two of my Pacific Lutheran University students, Elisa Hoelter and David Treichel, during the summer of 2009. To date almost 9,000 artifacts have been analyzed.

Obsidian is a volcanic stone made of silica that is created by the rapid cooling of volcanic ejecta. Because it cools so rapidly, it lacks a true crystalline structure (Cobean 2002). This quality makes obsidian ideal flaking sharp implements used for numerous slicing, cutting, and scraping activities. Most of the obsidian found on Aztec sites comes from relatively recent volcanic deposits scattered across Central Mexico, stretching from Veracruz on the Gulf to the western Mexican state of Michoacan bordering the Pacific Ocean (Glascock et al. 1988).

The Calixtlahuaca obsidian artifacts show some interesting variation concerning flaked stone tool production and use in Aztec period Central Mexico. Here are three patterns that stand out:

First, the collections are composed almost exclusively of gray obsidian (75%). Although data are limited, this contrasts with has been reported for other Aztec sites outside the Basin of Mexico, the location of modern day Mexico City and the heartland of the Aztec Empire. In Morelos more than 90% of the artifacts are made of obsidian from the Pachuca source in the modern state of Hidalgo, northwest of the Basin. Pachuca obsidian is typically green in color. We think, therefore, that Calixtlahuaca was supplied with obsidian by means of a different system than was the case for some of the other Aztec dominated sites in Mesoamerica. It is probable that much of it came from sources west of Calixtlahuaca, many of which are located in Michoacan. Future chemical analysis will be conducted to evaluate this proposition.

Second, most of the tools (66%) were derived from obsidian blades that do not appear to have been produced by craftsmen who lived at Calixtlahuaca. The Mesoamerican blade technology consisted of shaping a cylindrical “core” from which blades were then removed by “pressing” them off with a wooden implement (Hirth and Andrews 2002). Such a process results in byproducts of blade production that are minimally represented at Calixtlahuaca. This finding is interesting because at numerous Mesoamerican sites evidence suggests that blades were made in workshops by resident craftsmen. It seems likely, therefore, that blade tools arrived at the site ready-made for use, or were produced by traveling craftsmen who periodically visited the site and plied their wares in the market.

Third, many of the artifacts that were made using a biface technology (23%) do appear to have been shaped into various tools in Calixtlahuaca households  Biface technology entails the removal of flakes from two sides, or “faces” of a relatively flat piece of obsidian to make items such as projectile points (arrowheads) and other scraping and chopping tools. This finding is interesting because in Central Mexico evidence for the production biface tools in the majority of a city’s households is the exception rather than the rule.

These preliminary observations on the obsidian artifacts from Calixtlahuaca provide important new comparative information on flaked stone tool production and use in the provinces of the Aztec Empire.

I presented these observations at the recent Society for American Archaeology meetings:

Andrews, Bradford W. (2010)  Calixtlahuaca Obsidian: Initial Reflections of Lithic Technology on the Western Aztec Periphery. Paper Presented at the 75th Annual Meeting of the Society for American Archaeology, St. Louis, Missouri.

Artist’s reconstruction of Biface production in a Calixtlahuaca Household, illustration by Michael Stasinos.

References cited

Cobean, Robert H. (2002) A World of Obsidian: The Mining and Trade of a Volcanic Glass in Ancient Mexico. Serie Arqueología De México. Pittsburgh: Instituto Nacional de Antropología e Historia/University of Pittsburgh.

Glascock, Michael D., J. Michael Elam, and Robert H. Cobean. (1988) Differentiation of Obsidian Sources in Mesoamerica. Archaeometry '88. Eds. R. M. Farquhar, G. V. Hancock and L. A. Pavlish. Toronto: University of Toronto Press, 245-51.

Hirth, Kenneth G., and Bradford W. Andrews (2002) Introduction." Pathways to Prismatic Blades: A Study in Mesoamerican Obsidian Core-Blade Technology. Eds. Kenneth G. Hirth and Bradford W. Andrews. Los Angeles: The Cotsen Institute of Archaeology, University of California, 1-14.

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