VSSAC Monthly Meetings
Home of the Sutter Buttes Volcano Observatory
March Meeting Wednesday March 25th, 6:30 PM
This month’s presentation will be by
Lisa Hammersley
CSU Sacramento, Geology Department
"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 theirdiets, grinding tools became an important commodity flowing through ancienteconomies. Source analysis is one of the most important archaeometricmethodologies applied to the study of production and exchange of ancientcommodities. Source analysis of stone grinding tools in Central Mexico canbe challenging because volcanism is widespread and compositional variabilityin rocks within a restricted area may be limited. Evaluating and classifyingthis variability is fundamental to understanding the organization ofgrinding tool production and exchange. We have applied petrographic and XRF analysis to stone grinding tools and tosamples from likely stone sources from the Teotihuacan Valley that hadpreviously been analyzed by Neutron Activation Analysis (NAA). The NAA studyidentified geochemical differences in materials from different sources,established linkages between artifacts and some of these sources andidentified geochemical groupings of artifacts representing unidentifiedsources. However, our analysis indicates that without major element andpetrographic data, results from chemical fingerprinting can be misleading.For example, thin section analysis shows that while samples in some NAAchemical groupings display distinct mineralogical and textural features,others contain samples that show wide variability in rock type and likely donot come from the same source. Some materials are distinctive enough toallow for petrographic identification samples taken from a single source.Being able to classify samples petrographically provides a rapid and costeffective method for dealing with large sample sets. XRF analysis was usedto confirm petrographic grouping of samples that had not previously beenanalyzed and to provide major element data for the chemical groupings thatshowed wide variation in petrography. Our results illustrate the importanceof interpreting geochemical data within a geologic context.
The meeting begins with the traditional potluck at 6:30pm at the VSSAC Headquarters Central (AKA the "VSSAC Club House") Room 2004, Geology Dept/Placer Hall, on the campus of California State University, Sacramento. Make sure to bring along a dish to share and something to drink. If it needs to be hot, insulate it well. There are a couple of microwave ovens available too.
campus map
For more information about the meeting, contact Brian Hausback.
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