Archaeological investigations of stone tool heat treatment technology in southeastern Missouri: An experimental approach

Nearly sixty years of research demonstrate that stone tool heat treatment was practiced in prehistory and has a discontinuous, global distribution. Yet, the ability to positively identify heat treatment in the archaeological record or explain exactly how it works remains out of reach. A review of heat-treatment literature reveals that researchers attempting to identify the heat-treatment mechanism have used multiple experimental protocols. Reliance on replicative knapping to assess thermally induced mechanical alterations in heat-treated chert has introduced uncontrolled variation. Absence of explicit theory to guide such research has generated differing descriptions of results when rock is heated.; A research design sets out three questions: (1) What is the heat-treatment mechanism? (2) Is this mechanism reversible? (3) How can we identify heat treatment in the archaeological record? A series of experiments are performed to test some of the hypotheses from the heat-treatment literature. Once these are tested and found false, an hypothesis from fracture mechanics theory is forwarded and tested with additional experiments. The results of these experiments substantiate (do not reject) the hypothesis that water loss occurring between 250{dollar}spcirc{dollar}C and 375{dollar}spcirc{dollar}C makes chert a more homogeneous material which breaks more easily and predictably. Another series of experiments tests the reversibility of thermally induced water loss (the basis of the heat-treatment mechanism). These results reveal that the flatter, more specular fracture surfaces present on post-heating flake scars are not reversible. In the absence of physical post-depositional alteration of the archaeological record, lustrous flake scars can be used to identify heat treatment.; An archaeological application is based in evolutionary theory and a model for the use of heat-treatment technology is constructed to identify crucial variables necessary when considering the use and change in frequency of heat treatment over time. This model is applied to five lithic assemblages from Southeast Missouri. While a heat-treatment technology is identified in these assemblages, evidence for strong selection-driven change over time is lacking. It appears that there is selection against the use of heat treatment when manufacturing stone tools that receive abusive wear.