SESSION 12 - Silcrete as a lithic raw material in global contxt: geology, sourcing and techno-economics
Heat treatment of silcrete: thermal transformations, heating parameters and implications for the South African MSA

Silcrete is a tool stone of good quality; it was extensively used for knapping at various periods in Southern Africa, Western Europe and Australia. From the South African Middle Stone Age (MSA) on, stone knappers did not content themselves with the naturally available silcrete types but began to transform their properties by heat treatment. However, the absence of detailed studies about the mineralogy, crystallography and physical properties of silcrete led some researchers to compare silcrete heat treatment with heat treatment of flint as it was practised much later in Europe and North America. This comparison and its implications for understanding the MSA heat treatment instigators are problematic because silcrete behaves very differently upon heating than flint, hence it demands a different tempering procedure, a different investment in time and resources. In this paper, the heat-induced transformations of silcrete, the heating parameters resulting from these transformations, the appropriate heating environments and the procedures that best allow silcrete heat treatment are described. Direct archaeological data on the procedure actually used for silcrete heat treatment during the South African MSA is then presented.