Late Classic and Epiclassic Obsidian at Santa Cruz Atizapan, Toluca Valley, México

Santa Cruz Atizapan Obsidian

More than 11,000 obsidian objects were recovered during three seasons of field excavation at the site of Santa Cruz Atizapan (Sugiura 1998c; 2000; 2003). The analysis of this assemblage is significant for three reasons: (1) Obsidian use at the Santa Cruz Atizapan site was adapted to a unique lacustrine environment, (2) The lack of usable obsidian sources in the Toluca Valley meant that its residents must have been provisioned with obsidian from other regions, and (3) The occupation of the Chignahuapan islands from Late Classic through the Epiclassic periods allows us to investigate the changing character of obsidian within the broader political, economic and social restructuring that took place with the demise of the Teotihuacán state at the end of the Late Classic.

The vast majority of obsidian objects are made of grayish-black obsidian which is often translucent and displays a banded color texture ²  (72%). Visual analysis with a 20x hand lens and consultation with other archaeologists leads us to believe that this obsidian was obtained from sources in the current state of Michoacán, northwest of the Toluca Valley. Neutron Activation Analysis is currently underway and will allow us to draw a more significant conclusion regarding the origins of this and other obsidian categories (Figure 2, shown above). Semi-translucent black-gray obsidian with a veined color texture represents nearly 14% of the total obsidian. It is distinguished from the previous grayish-black obsidian for several reasons. One, it lacks the distinct gray banding color texture that is found in the other obsidian; two, it displays a consistently veined color texture; and three, it is visually identical to a sample of obsidian obtained from a previously undocumented outcrop in the northern part of the Toluca Valley. ³   This obsidian outcrop has yet to be fully explored and its archaeological value is presently unknown but it does represent the first evidence for a regionally available high quality raw material source. Santa Cruz Atizapan obsidian and samples from the source outcrop will be compared through Neutron Activation Analysis to determine if they are the same material and whether we have evidence for intra-valley procurement of obsidian during the Late Classic and Epiclassic periods. Green obsidian, almost certainly from the Sierra de las Navajas source in the state of Hidalgo, represents 7% of the entire assemblage. The remaining 7% is comprised of black opaque (1%), light gray translucent (1%), dark gray opaque (1%), light brown translucent/iridescent (2%); greenish-gray banded translucent (1.5%) and indeterminate types. ⁴   These "types" are also currently being sourced via Neutron Activation Analysis.

Click on figure to view larger, higher resolution image.

The majority of obsidian artifacts are what Clark and Bryant (1997) termed third series prismatic blades (Figure 3, shown above). The consistently shaped blades have parallel cutting edges and dorsal ridges. Their trapezoidal longitudinal cross-section creates the "prismatic" facets that give the objects their name. Because these objects represent the final product in core-blade technology and because there is limited evidence for substantial obsidian working at the site, it seems that obsidian objects arrived at the Santa Cruz Atizapan site as finished, ready to use objects. The small numbers of polyhedral cores present in the assemblage are exhausted and further suggest that few if any prismatic blades were produced locally from imported cores. Several antler tines were recovered during excavations but these could have been used for pressure flaking prismatic blades, worn bifaces and other tools. Despite this, we must still consider the possibility that Epiclassic period obsidian workshops located within the boundaries of the nearby La-Campana civic-religious center might have provisioned the surrounding islands with prismatic blades. Only future work at the La-Campana site and at more man-made islands will offer a clear indication.

Twenty-five polyhedral core fragments were identified during the analyses. Sixteen of these 25 cores are so fragmented that they represent less than 25% of their estimated pre-break size. Only two cores were found to be complete specimens. Twelve cores are of the grayish-black variety, while 11 were recorded to be the black-gray variety which may be local to the Toluca Valley. Only 2 core fragments are of green obsidian. All of the cores are thin and exhausted; very likely at or near the end of their use as polyhedral cores.

Numerous obsidian tools were produced by simply pressure-flaking broken segments of prismatic blades. Several identified forms are consistent with those found at many Mesoamerican sites (see Figure 3). Needles (N=35), eccentrics (N=83), and projectile points/hafted bifaces (N=12) are the most recognizable objects made from blades. Needles, used for blood-letting rituals throughout much of Mesoamerica, average 6 mm in width and 2.5 mm in thickness. Our sole complete needle is pointed on both ends and measures 59 mm in length. Grayish-black, gray and green obsidians are nearly equally represented, but surprisingly, 40% (N=14) are made from brown translucent obsidian.

Prismatic blade segments were also fashioned into crescent and trilobed eccentrics. These are most often made of the abundant grayish-black obsidian (N=42) although a few are made of green, gray and black-gray obsidian. Their modification varies greatly as some are well shaped and others poorly pressure flaked. None exhibit evidence of having been shaped or polished by abrasion. Projectile points made from prismatic blades are few in number and it is not surprising to note that all but two are made of the most common grayish-black obsidian at the site. These objects tend to have only their outer edges bifacially modified. The small number of prismatic blade projectile points recovered suggests that they were not as highly regarded as regular hafted and unhafted bifaces.

Of interest in the Santa Cruz Atizapan obsidian are prismatic blades modified to create alternating cutting edges by pressure flaking both dorsal and ventral surfaces (N=74) (Figure 4, shown above). Lateral projections, the width of the original blade, are often left at the blade’s midpoint creating a top and bottom half. The remaining blade sections are then intensively pressure flaked in a consistent pattern. Viewed from the dorsal surface, with the prismatic facets of the blade facing up, the bottom-left and upper-right edges of the blade are heavily retouched. The opposing upper-left and bottom-right edges are alternately retouched on the ventral side of the blade. All of these tools are made of grayish-black obsidian. Their function has not been determined, but we do believe they were used in domestic utilitarian contexts because they are widely distributed at the site and were not recovered from ritual or ceremonial contexts.

Click on figure to view larger, higher resolution image.

Hafted and unhafted bifaces make up 3% of the entire assemblage (N=312). These tools are produced by percussion and pressure flaking both faces of an obsidian blank. They represent a completely different technology than that utilized to produce prismatic blades. Hafted bifaces include side, corner and basal notched projectile points (Figure 5, shown above). The variation in form and hafting location are notable in this assemblage. The majority of bifaces are made from grayish-black obsidian (N=134), but surprisingly we found that greenish-gray was the second most common obsidian identified (N=50). Brown (N=34) and Pachuca green obsidian (N=34) are also well represented. The only two non-obsidian bifaces recovered from the Santa Cruz site are made of red rhyolite and quartzite.

Endnotes

2. Color Texture denotes the way colors are distributed in the obsidian. Although this grayish-black obsidian is often described as gray colored in other literature, the black color is emphasized to distinguish it from the distinctly gray banding.

3. The high quality obsidian source was recently located by a Toluca Valley archaeologist who retrieved samples from a road cut near the source region.

4. Obsidian objects were divided into 25 different "type" categories based on color, color texture, light transmittance, surface luster, surface texture, and the presence of impurities in the material. Many of these categories are condensed and described only by color designations in this report to reflect my confidence that the N.A.A. study will establish that many types represent variations of the same obsidian source. As such it also facilitates a discussion of the preliminary conclusions offered here.

Previous Page  |  Table of Contents  |  Next Page