Summary

In archaeology, heat treatment is the intentional transformation of stone (normally sedimentary silica rocks) by fire to produce materials with improved fracture properties. It has been documented on all continents, from the Africa Middle Stone Age up to subrecent times. It was an important part of the Mediterranean Neolithic and it sporadically appeared in the Paleolithc and Mesolithic of Asia and Europe. It may have been part of the knowledge of people first colonizing North and South America, and it played an important role for toolmaking in the Australian Prehistory. In all these contexts, heat treatment was normally used to improve the quality of stone raw materials for tool knapping; especially its association with pressure flaking has been highlighted, but a few examples also document the quest of making tools with improved qualities (sharper cutting edges) and intentional segmentation of large blocks of raw material to produce smaller, better-usable modules (fire fracturing). Two categories of silica rocks were most often heat-treated throughout prehistory: relatively fine-grained marine chert or flint and more coarse-grained continental silcrete. The finding of stone heat treatment in archaeological contexts opens up several research questions on its role for toolmaking, its cognitive and social implications, and the investment it required. Important venues for research are, for example: Why did people heat-treat stone? What happens to stones when heated? How can heating be recognized? By what technical means were stones heated? Which cost did heat treatment represent for its instigators? Answering these questions allows light to be shed on archaeologically relevant processes like innovation, reinvention, convergence, or the advent of complexity. The methods needed to produce these answers, however, often stem from other fields such as physics, chemistry, mineralogy, or material sciences.