ROCK PROPERTIES AND MATERIAL SELECTION FOR BLADE MANUFACTURE IN UPPER PALEOLITHIC JAPAN

Abstract

For a comprehensive understanding of material selection and exploitation for blade manufacture, an objective estimation on the material properties of actual shale artifacts remaining in an Upper Paleolithic site in northeastern region of Japan was performed. The Vickers microhardness test and observation of crack propagations were conducted along with microstructural analysis on shale samples. In order to accentuate the material inclination for blades, shale types used for blade production were set against those used for bifacial points. As a result, the hardness values of shale used for blades were comparatively uniform and higher than 6.0 GPa, while those of bifacial points varied widely and were mostly lower than those of blades. Considering the fact that higher hardness values can provide tools with superior cutting ability and edge durability, the selection of harder materials for manufacturing blades was reasonable for maximizing tool quality. In addition, it turned out that most materials used for blades were capable of creating comparatively straight and uniform cracks under a certain pressure load, which should be adequate for fabricating straight, standardized, and long blades. The results suggest that specific rock materials with certain mechanical and fracture properties were preferably selected by Paleolithic people for manufacturing blades, and these selections were reasonable in terms of maximizing tool quality and flaking property. Thus, detailed material data on prehistoric tools have great potential to provide ample information on raw material selection and exploitation.