Superficial reddening of silcrete may indicate low temperature heat treatment

Abstract

Heat treatment of silica rocks has been used to make a range of inferences about past human behaviours, including cognitive evolution. Several measures have been proposed to identify heat treatment, some of which index different kinds of changes, and potentially different underlying behaviours. In this paper we attempt to disentangle the effects of heating on colour change and the surface roughness of silcretes at relatively low temperatures. We demonstrate that colour change is a progressive process initiating at the rock surface before extending into the interior of the rock. Changes to surface roughness, however, occur pervasively throughout the rock even at relatively low temperatures (250 °C). Consequently, low temperature heat treatment may produce different signals in colour change and surface roughness that allow its archaeological identification. We then provide an example from the Middle Stone Age of South Africa.