March Meeting Wednesday March 25th, 6:30 PM 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. |