Source Characterization of Stone Grinding Tools from the Teotihuacan Valley, Mexico

Igneous stone grinding tools were crucial to daily sustenance in prehispanic Central Mexico. As ancient peoples increasingly depended on maize in their diets, grinding tools became an important commodity flowing through ancient economies. Source analysis is one of the most important archaeometric methodologies applied to the study of production and exchange of ancient commodities. Source analysis of stone grinding tools in Central Mexico can be challenging because volcanism is widespread and compositional variability in rocks within a restricted area may be limited. Evaluating and classifying this variability is fundamental to understanding the organization of grinding tool production and exchange.

We have applied petrographic and XRF analysis to stone grinding tools and to samples from likely stone sources from the Teotihuacan Valley that had previously been analyzed by Neutron Activation Analysis (NAA). The NAA study identified geochemical differences in materials from different sources, established linkages between artifacts and some of these sources and identified geochemical groupings of artifacts representing unidentified sources. However, our analysis indicates that without major element and petrographic data, results from chemical fingerprinting can be misleading. For example, thin section analysis shows that while samples in some NAA chemical groupings display distinct mineralogical and textural features, others contain samples that show wide variability in rock type and likely do not come from the same source. Some materials are distinctive enough to allow for petrographic identification samples taken from a single source. Being able to classify samples petrographically provides a rapid and cost effective method for dealing with large sample sets. XRF analysis was used to confirm petrographic grouping of samples that had not previously been analyzed and to provide major element data for the chemical groupings that showed wide variation in petrography. Our results illustrate the importance of interpreting geochemical data within a geologic context.