In the past, chert artifacts have been identified on the basis of color variations alone, disregarding a whole range of textural, diagenetic and structural characteristics. Little or no attention has been paid to the non-chert lithic materials used in stone-tool manufacture, such as hornfels, slate, and various types of groundstone, as these materials don't have many visually distinctive characteristics. Traditional methods of lithic sourcing and identification of quarry locations have often been problematic because the superficial descriptions of the lithics have resulted in the incorrect assignment of lithic materials to only a few sources. Techniques such as neutron-activation analysis and x-ray fluorescence don't resolve these difficulties, because similar source materials may have similar chemistries. Moreover, the limited number of baseline quarry chemistry studies means that chemistries tend to be interpreted only in light of known quarries.
LaPorta Geological Consultants has now developed a new, objective method of provenancing stone tools, one that allows the archaeological professional to not only identify a particular source material for an artifact, and even determine the spatial distribution of potential source areas. How do we do it? We combine a broad-based knowledge of regional geology (the geologic catchment) with an enhanced description of a variety of lithic materials; including chert, volcanics, vein quartz, quartzite, hornfels and groundstone (through petrographic and/or SEM/EDX analyses). Distinctive textural and structural characteristics of these lithic materials, representative of their origin within a particular geologic setting, can be used to identify their sources once compared to samples in our lithic database. Knowledge of the geologic structure and stratigraphy of a region through geologic mapping then permits us to delimit the geographic distribution of those lithic sources.
The results of our new approach open a wide range of opportunities for the archaeological professional. Now, the geographic and geological settings of prehistoric quarries are predictable. Deeply disturbed plow-zone sites can be archaeologically relevant because unique lithic scatters and activity areas can be differentiated. Intra-site analyses, including refitting studies, are also possible owing to the detailed descriptions of lithic source distributions. An additional bonus is the ability to track the changes in lithic exploitation, and thus prehistoric land utilization patterns of lithic materials, over time and space.
Please see our case studies for some examples of the petrographic characteristics we can use to help distinguish between difference raw material sources. We can produce and individually tailored petrographic atlas of similar images for any client's needs - please contact us for further details.
***Updated Spring, 2014