CHERT ARCHAEOMETRY USING XRF ANALYSIS

Chert typically consists of 65-95% SiO₂, plus Al, Fe, Mn, Ca, Na, K, Mg, Ti, and rare earth elements (Boggs, 2011). I collected 14 chert samples from 6 localities in West and central Texas, including Alibates chert from the Permian Quartermaster Formation near Amarillo, Ordovician Maravillas Formation and Devonian Caballos Novaculite from the Marathon uplift, and chert nodules in Lower Cretaceous formations in the Big Bend region. I plan to use X-Ray Fluorescence (XRF) analyses to seek matches between chert archaeological artifacts donated to Angelo State University and chert samples I collected. Similar XRF studies have been done on obsidian arrowheads, which led to the tracing of trade routes among ancient societies (Aoyama et al., 1999). Research has focused on finding effective ways to analyze chert samples. Other ASU students constructed a lead box which encloses an Ampted ADMCA X-ray detector used to analyze samples. Experimental data determined that 120 degrees is the optimum angle to set the detector from the X-Ray emitter. I determined that the freshly sawed chert surfaces yield less background noise on graphs than weathered surfaces, likely because scattering is minimized when analyzing a flat surface. I fit background noise generated in data collection to a fifth-order polynomial trend line, and normalized each data set by subtracting out the background noise. Calcium and iron define the two most well-defined peaks. I analyzed Calcium and Iron peaks of each sample using the full-width-half-maximum (FWHM) method to estimate percentage of calcium and iron in each sample. I will plot the percentage of iron versus calcium in each sample on one graph of all samples to see if chert samples from different regions plot in distinct clusters. Next, I will determine Calcium and Iron percentages of archaeological chert samples and see if they plot in the same clusters.