Raw material properties investigations: Knapper skill interaction with rock mechanical properties.

Joanne Munga1

  1. Department of Human Paleobiology, George Washington University, Washington D.C, USAEmail: joannem@gwmail.gwu.edu

Résumé

Studies on experimental knapping have previously provided some insights on determining the qualities of stone used in tool production. However, given the variability in rock properties it is sometimes difficult to relate these to archaeological materials.Previous studies have used visual inspection of rocks to identify key features related to stone knapping ability. These visual inspections are usually related to the size and variation of crystals, especially in igneous rocks. This is particularly evident in igneous rocks that make up the majority of Earlier Stone Age assemblages in East Africa. Visual properties of stones that are relevant to artifact manufacture can be quantified using image analysis (ImageJ 4.x). The relationship between mechanical properties of specific raw materials (as measured by Leeb hardness and Young’s elastic modulus) and visual features related to the size, shape and frequency of phenocrysts was investigated. Sixty-six sections of 6 lithologies used by hominins at the ca. 2-million-year-old Oldowan site of Kanjera South (western Kenya) were prepared and 1,986 images (40-150x magnification) of these sections were analyzed with ImageJ 4.x to document phenocryst size and frequency.
Results revealed that some of the visual properties covary more strongly with raw material elasticity than hardness. To further investigate these relationships, 30 cobbles with known elasticity values were knapped by individuals with varying skill levels, to investigate the impact of elasticity on various measurable flake attributes.Expert knappers produced larger and thinner flakes with higher frequencies of feather termination using raw materials having higher elasticity values. Intermediate and novice knappers can make large flakes with low quality raw materials but see little improvement with more elastic lithologies. The experiments suggested that the impact of raw material quality on archaeological assemblages is interrelated with knapper skill.


Type Poster
Langue du texte intégral English
Thématiques AFR.001: Recent Advances in Early Stone Age Studies in Africa, New Insights on the Oldowan and the Acheulian Stone Technology
Mots-Clés Raw material quality; Oldowan technology; Raw material properties; Experimental knapping;
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