Volcanic textures control the mechanical behaviour of Mesoamerican obsidians

Obsidian-natural volcanic glass-was exploited for millennia and played a central role in the technological and socio-economic development of pre-Hispanic societies across Mesoamerica. The selection of obsidian from specific deposits has been linked to differences in visual appearance and patterns of use; however, the material properties underlying these preferences remain poorly understood. Here, we investigate obsidians from the Sierra de Las Navajas deposit-the most exploited obsidian deposit in Mesoamerica. We combine ball-on-three-ball measurements to quantify fracture strength with nanoindentation to quantify hardness, complemented by X-ray tomography and scanning electron microscopy. Mechanical behaviour varies among obsidian families and sampling locations and is primarily controlled by textural characteristics, notably the size and morphology of inclusions. These textures reflect distinct volcanic processes that govern material performance. Our results establish the first quantitative framework linking volcanic textures and mechanical performance in obsidians from Sierra de Las Navajas, providing a physical basis for evaluating how geological processes may have influenced obsidian utilization in pre-Hispanic Mesoamerica.