Rock physics and the circulation of Neolithic axeheads in Central Europe and the western Mediterranean

Slightly retrograded rocks for edge-ground tool manufacture were used in two different supply systems during recent European prehistory. Mechanical properties of five of these rock types were tested to determine if the most exploited and circulated materials were also the most adequate ones. A series of mechanical tests were chosen to characterize their hardness, elasticity, resistance to friction, and Charpy impact toughness. The results were compared with petrographic variables (mineralogical composition, density, homogeneity, grain size, anisotropy, and presence of retrogression). Subsequent correlations between the tested mechanical properties confirm that density is a good proxy to estimate hardness, elasticity, and resistance to friction of the given rocks. It emerged that the amphibolic hornfels (MJH) most used in Neolithic Central Europe and circulated over large distances was harder than most other tested rocks and compositionally more homogeneous. On a broader European scale, however, MJH is not superior in quality to Iberian gabbros. Both rocks show much poorer mechanical qualities than Alpine high-pressure meta-ophiolites, which were largely ignored by the Early Neolithic populations of Central Europe. Analogies from the Iberian Peninsula also indicate that rocks comparable in quality to MJH, and transformed into Neolithic axe heads, only circulated in an area a few hundred kilometers from their sources. Long-distance transport of MJH is thus only partially explained by its mechanical qualities and rather reflects a wide and well-functioning social and economic network established over large parts of Central Europe which has no parallels in the European Neolithic.