Arizona Salado turquoise: source studies with proton-induced X-ray emission and X-ray diffraction

We compare the composition of turquoise source materials from Arizona to prehistoric blue-green stone artifacts recovered from Salado platform mounds (ca. AD 1275-1450) in the Tonto Basin of Central Arizona. Turquoise samples from known source areas in Arizona including Kingman, Castle Dome, in the Globe- Miami area are compare with others that may have been potential sources of turquoise artifacts recovered from the Salado platform mounds. The complementary techniques of proton-induced X-ray emission (PIXE) for chemical analysis and X-ray diffraction (XRD) for mineralogical signatures are used for nondestructive characterisation of both source area samples and archaeological artifacts. The results of the source area sample characterisations are compared quantitatively with the results of archaeological samples, which are evaluated in terms of their likelihood of being from each of the regional sources. The combination of mineralogical and chemical data to identify source materials provides a more thorough identification of the complex variations within turquoise related materials that may not be distinguished by visual inspection. The PIXE and XRD analysis are compared using a set of multivariate statistics including principal components analysis and discriminant analysis. Additionally, a set of Munsell colour charts specifically for the blue-green range of colours is used to objectively qualify colour in comparison to chemical and mineralogical signatures, as colour alone is not a reliable indicator of composition. The results provide objective data to assess directionality of procurement of turquoise and regional social and economic ties to better understand Salado regional connections during this dynamic period in the American Southwest.