Lithological Identification of Stone Tools Through Microscopic Manufacturing Traces on Ductile Metals: A Tribological Experimental Study

This study presents an experimental tribological approach to the analysis of microscopic manufacturing traces produced by different lithologies used as tools in metalworking processes. The aim is to establish diagnostic criteria for inferring the lithological family of stone tools involved in the production of hammered metal artifacts from the archaeological site of El Caño, Panama. A comparative experimental framework was developed using basalt, granite, quartz arenite, andesite, and limestone to generate controlled traces on aluminum sheets as an analog for ductile metals. Petrographic characterization was conducted through thin-section analysis, while the resulting traces were examined using scanning electron microscopy (SEM) and quantified through image analysis. Both morphological attributes and metric variables—including trace width and grain size (Feret diameter)—were analyzed statistically.The results show that lithological microstructure plays a decisive role in trace formation. Two morphologically distinct trace types (A and B) were identified. While type A traces occur in all lithologies, type B traces are restricted to sedimentary rocks and are associated with more discontinuous abrasive contact configurations. Trace width emerges as the most discriminant metric variable, whereas no direct proportional relationship is observed between grain size and trace dimensions, indicating a non-linear interaction between abrasive elements and metal surfaces. The observed differences demonstrate that both trace morphology and trace dimensions are controlled by the organization of abrasive components within the active surface rather than by individual mineral properties alone. These findings indicate that microscopic traces reflect functional surface configurations resulting from the interaction between texture, matrix, grain exposure, and microtopography. Diagnostic criteria can therefore be defined based on combinations of attributes—such as trace type, variability, density, distribution patterns, and morphology—rather than on absolute metric thresholds. This study provides a methodological framework for inferring lithological families and contributes to the interpretation of technological signatures in archaeometallurgical contexts where direct access to raw materials is not possible.